Silviculture and forest genetics

SILVICULTURE AND
FOREST GENETICS
SFB701
COMPILED BY: ABIRAL ACHARYA AND SMRITI PAHARI
JANUARY, 2020
Tribhuvan University, Institute of Forestry

Compiled by Abiral Acharya and Smriti Pahari
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UNIT 1: PLANTATION SILVICULTUTRE (5)
1.1 Introduction and scope of plantation in Nepal
Plantations of a wide range of tree species have assumed an important place in our world, providing
wood for industry, fuelwood and animal fodder, protection from adverse environments and for the soil,
as well as amenity and aesthetically pleasing landscapes. Silvicultural knowledge of this particular
branch of forestry first developed in Europe more than two centuries ago but in many parts of the world
is still in a process of rapid evolution as more and more plantations are established to meet specific needs.
The term silviculture refers to certain aspects of theory and practices of raising forest crops (Champion
and Seth 1968). It is defined as the art and science of cultivating forest crops (Anon 1966). Silviculture
includes both (a) Silvics and (b) its practical application. Silvics has been defined as the study of life
history and general characteristics of forest trees and crops with particular reference to environmental
factor as the basis for the practice of silviculture (Anon 1966).
The word “Plantation” is synonymous to artificially regenerated crop and it is defined as a forest crop
raised artificially, either by sowing or planting. Artificial regeneration includes (i) reforestation and (ii)
afforestation.
Forest stands established by planting/seeding in the process of afforestation or reforestation either of
introduced (exotic) or indigenous species with minimum area of 0.5 ha, tree crown cover of at least 10%
of land cover, and total height of adult trees above 5 m are termed as Plantation Silviculture (FAO).
Rubber plantation (for fibre) , previously under agri. Plantation, is now under forest plantation. New
forest plantation are established globally at the rate of 4.5 million ha/yr
 Industrial plantation-48%
 Non-industrial plantation-26%
 Plantation for unspecified use-26%
 Total planted forest: Africa A/P LAC Total
(Millon ha) 0.95 12.0 9.4 22.4 (2010)
0.82 38.3 5.6 44.8 (2005) Source: country profiles in ITTO (2011)
 Distribution of forest plantation
Asia-62% Europe-17%, N. and C. America-9% S. America-6% Africa-4% Oceania-2%
(source: Global Forest Resource Assessment, FAO, 2001)
 Deforestation (mainly conversion to agri.)-13 million ha/yr
 Increase for industrial plantation and decrease for non-industrial plantation
 Increasing potential for plantation investment to offset carbon emissions
 Tropical and subtropical forest plantation constitute 44.7% of global resource
 Annual rate of forest plantation establishment in tropical and subtropical countries are more than 4 million
ha/yr
Why plantation?
1. Past and continuing destruction of natural forest.
 In the past 150-200 years, forest destruction has taken place in every country. Forest
disappears at a rate of 15-20 million ha/year in developing countries.
 Between 1990 and 2010, more than 30% of tropical forest was cleared in Asia and 15-
20% in rest of the world.

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2. Problem of access to existing forests; physical limitation, high slope, mountains, swampy ground, no
infrastructure of road, communication and service.
3. Unsatisfactory natural regeneration due to biotic influence.
4. High productivity of plantation than existing forest.
5. High demand of industrial materials.
 Teak-10.5 cum/ha/yr, E.cameldulensis-30 cum/ha/yr
 Pinus caribaea-40 cum/ha/yr, Sissoo-18.1 cum/ha/yr
 Pinus roxburghii-15 cum/ha/yr, tropical high forest (managed)-0.5-7 cum/ha/yr
 Tropical hardwood plantation-25-35 cum/ha/yr
 5. Environmental protection
 Plantations cover more than 100 million ha worldwide
 Plantation for reclaimation of degraded forest lands, protection of watersheds, plantation for
environmental purposes
 Malaysia has 250,000 ha of forest plantations (2005)
 China, Russian Federation, USA, India and Japan each have established more than 10 million ha
of forest plantations
Plantation forestry in Nepal
 Plantation programme started from 1st
five year plan (2013-17)
 1st
five year plan (2013-17) 153 Acre
 2nd
five year plan (2017-21) 2,454 ha
 3rd
 From 2023, afforestation program was launched as a separate project up to 2028. The plantation
was confined to Kathmandu valley.
 From 2029 onwards, the program was launched in Terai and middle mountains
 4th
 5th
 6th
five year plan (2037-42) 12,096 ha (community forest development project)
 7th
 During period from 2037-047, area under forest plantation has increased by 14% in Nepal (World
Resource Institute, 1998)
Major plantation programmes
 Sagarnath forest development project/ program (2035/36) 11,000 ha
 Ratuwamai plantation project (2040/41) 2,900 ha
 Nepalgunj forest development project, Kohalpur (2043) 5,000 ha
 Chautara forest development project 2035/36
 Integrated rural development project in 6th
five year plan
 Hill forest development project 2040-41.
 Private forests, farm forestry – 1985 by Butwal plywood.
 Leasehold forestry 2049 Act.
 TCN plantation in terai, species was sisoo only.
 Plantation trials of Research Division in different ecological zones. Comprises mainly of
tropical pines.
 Provenance trial of sisoo at Adavar.

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 Pakribas Agriculture Research Centre- sisoo, gurans, ficus, utis, khote sallo, gobre sallo, okhar,
katus, bakaeno, sal, etc. on trial planting.
 Research is on fodder species on CF.
 Tamagarhi Taungya Plantation 1976-89, more than 50 families.
 CF plantation of more than 5000 ha supported by Nepal Australia Forestry Project and CF
development project in hills.
 Terai CF project launched in 1984, covered 13 districts, targeted 26,000 ha, achieved 19,260 ha
including 13,500 ha private plantation.
 Departmental plantation of 2,250 ha. Road, canal, 2,900 ha agro-forestry.
Constraints on plantation establishment
1. Ability of a species to grow well on site available
2. Difficulty of raising certain spp. In the nursery / lack of knowledge of satisfactory techniques
3. Technical manpower availability
4. Availability of suitable land
5. Administrative
6. Adequate fund
Scope
Beautiful Flowering Trees (Bauhinia variegata (Kachnar), Butea monosperma (Palas), Cassia fistula
(Amaltas), Crataeva religiosa (Barna), Erythrina indica (coral tree), Lagerstroemia flos-reginae (Jarul),
Plumeria alba (Champa))
Fast Growing Trees (.Anthocephalus cadamba (Kadam), Ficus religiosa (Peepal), Ailanthus excelsa
(Maharuk), Albizzia falcataria, Bauhinia variegata (Kachnar), Eucalyptus, Popular, Sissoo, Melia
azadrich)
Medicinal Trees (Aegle marmelos (Bel), Azadirachta indica (Neem), Bauhinia variegata (Kachnar),
Butea monosperma (Palas), Cassia fistula (Amaltas), Cinnamomum camphora (Kapur), Emblica
officinalis (Amla), Ficus glomerata (Gular), Moringa oleifera (Drum stick))
Trees with fragrant flowers (Albizzia lebbeck (Siris), Pterospermum acerifolium (Kanak Champa),
Michelia champaca (Champ), Champa varieties, Alstonia scholaris)
1.2 Plantation in the Tropics
Plantation before 1900
 Bible records Abraham planting a tree Tamarisk tree which is historical record exists.
 It is actually in the tropics, in the Srilanka where the Bodhi tree (Ficus religiosa) is recorded
about 220 BC.
 The present development of manmade forestry can be traced back to the sixteenth and
seventeenth centuries when exploration and expansion of European influence took place. They
collected numerous species from the world to scientific study among them many species failed.
 But as early as 1680, Teak was introduced in Srilanka which became success.
Plantation during 1900-1945
 By 1945, in South Africa 180,000 ha plantation of tropical pines and eucalyptus species was
done.

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 In Australia (Queensland) 9,800 ha of Araucaria and pines planted.
 In India, by 2nd
world war, 80,000 ha of teak was planted and many more trials of eucalyptus.
 In Brazil, between 1920 and 1930, several hundred thousand hectares of eucalyptus were planted.
Plantation during 1945- 1965
 In China, 100,000-450,000 ha/ year – china fir (cunninghamiana lanceolata) was planted in south,
most tropical provinces.
 By 1958 in Africa largest block plantation 41,000 ha. The Usutu forest in Swaziland. Infact
between 1945-65 more than 80,000 ha or 5% of the total land surface.
 In 1965, the approximate area of plantation in the tropics was 3.5-4.0 million ha (FAO, 1967)
including those of Southern China.
Plantation during 1966-1980
 Between 1966 and 1977, the rate of planting in Brazil rose from 40,000 ha/ yr. By 1980, 100,000
ha were planted and pulp mill operated.
 In 1980, according to FAO (1988) of 11.5 million ha plantation in tropical countries, among them
7.2 million ha for industries and 4.3 million ha for non-industrial purpose.
 World forestry congress held in 1972 “The Forest and Economic Development”; in 1978, “Forest
for People”, FAO 1978 “ Forestry for Rural Communities”, “Trees, Food and People”, “Land
Management in the Tropics” “Forest Energy and Economic Development” etc.
 In the 1970, many organizations involved to encourage tree planting in tropics such as World
Bank, ITTO, many NGOs, INGOs, ICRAF, FAO, USAID, Winrock, Danida, Finida, Swiss etc
have been supporting for planting trees in tropics.
Program of planting up to 2000
 In Burundi, 300,000 ha
 Malaysia, 500,000 ha
 Ethiopia, 3.5 million ha
 Indonesia, 300,000 ha
 India, 17 million ha
 Brazil. 12 million ha
 China increases coverage by 12-20%
 Nepal increase 42% coverage
Plantation characteristics
 Plantations are usually near or totally monoculture whereas natural forest would contain a far
more diverse range of tree species
 Plantations may include tree species that would not naturally occur in the area. Pine, spruce and
eucalyptus are widely planted beyond their natural range due to their fast growth rate, tolerance
of rich or degraded agricultural land and potential to produce large vol. of raw materials for
industrial use
 Plantations are always young forests in ecological terms (10 to 60 years rotations)
 Trees planted can represent best genetic material available and be carefully fitted to the site
 Growth of planted trees can often be improved by fertilization or by reducing any competing
vegetation
 With planting, it is possible to govern the density, spacing pattern, species composition, and
genetic constitution of new stand more precisely
 More dependable kind of regeneration

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1.3 Artificial Regeneration in Difficult sites
Renewal of a forest crop by sowing, planting or other artificial means. Normally such a crop is called-
Plantation.
i. Sowing of seeds directly on an area
ii. Planting or transferring of seedlings or plants in the area to be regenerated.
iii. Wilding (natural seedlings used in planting).
Plantation
i. Reforestation: plantation on a site having forest vegetation before.
ii. Afforestation: plantation on a site where forest vegetation has long or always been absent.
Objectives of Reforestation:
i. To supplement natural regeneration
ii. To give up natural reg. in favor of artificial regeneration.
iii. To restock forests destroyed by fire or other biotic factors.
iv. To change the composition of crops
v. To introduce exotics.
Objectives of Afforestation:
i. To increase the production of timber.
ii. To increase the production of fuel and small timber.
iii. Improvement of Agro-ecosystem
iv. Moderation of climate.
v. Soil conservation.
vi. Protection of catchment of rivers.
vii. Increasing natural beauty of landscape.
Afforestation of Saline and Alkaline Soil
Nature of Saline and Alkaline Soil: The presence of an excess of sodium salts and the predominance of
sodium in the exchangeable complex are divided into the two main groups:
(1) Saline Soils: Saline soils contain an excess of sodium salts
(a) Saline-alkali soils: When they contain soluble salts in excess they are known as saline-alkali
soils.
(b) Non-saline-alkali soils (Alkali soil): When they do not contain soluble salts, they are called non-
saline-alkali soils.
(c) Degraded alkali soils: Under certain circumstances the clay complex of some alkali soils is
broken down to give rise to degraded alkali soils.
(2) Alkali Soils: In the case of alkali soils, the exchange complex contains appreciable quantities of
exchangeable sodium. Such soils may or may not contain excess salts.
Locality Factors: Several factors contribute to the development of salinity and alkalinity in the soil.
 Important factors are arid and semiarid climate.
 Impervious hard sub soil due to clay or kankar pan
 Basin shaped topography.
 High water table.
 Impeded drainage
 Salt bearing sub –strata

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 Excessive canal irrigation
 Use of saline and brackish water for irrigation and
 Flooding by sea water.
 PH is usually high
 The pressure of human and animal population is high
Soil Preparation: The principal requisites of good soil working in the areas are:
1. Maximum retentivity and utilization of rain water.
2. Maximum reduction of salt concentration in the active root zone of young plants through
leaching.
3. Use of soil amendment (even import of salt free soil) where necessary.
4. Breaking of kankar pan when it exists subsoil.
5. Production of loose soil suitable for rapid root development
Keeping the above points in view, various methods of soil working i.e. pits, augar holes and trenches of
different sizes and shapes are used in different places. The usual method is to dig pits and patches.
 In areas of kankarpan the pits are fairly deep (1.2m) to perforate the pan.
 In patches of good soil, it is filled back.
 Salt affected soil is treated for amendment.
 In worst areas soil is changed with imported salt free soil to provide a favorable medium for
initial growth.
 In waterlogged areas mounds are made.
 For Permanent amendment of soil gypsum, farmyard manure or molasses should be used.
Reclamation: This soil can be reclaimed by using the following.
 Application of gypsum
 Use of pyrites
 Drainage
 Crop management practice
 High salt tolerant crops
 Land levelling and construction of bunds
 Adequate provision of drainage
 Assured source of good quality irrigation water
 Application of amendments
 Leaching
 Nutrient management
Choice of species: Careful selection of species for afforestation of salt affected soils is required.
 Species should be capable of producing a prolific root system, able to resist salt content and thrive
well under conditions of arid climate with low moisture supply.
 The species chosen should also be drought resistant as the high salt contents in soil solution also
cause physiological drought.
 The choice of species is therefore, governed by the nature and amount of salt, relative proportion
of sodium ions, physical conditions of the soil and amount of moisture regime.

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 Acacia catechu,Azadirachta indica ,Albizia procera Acacia arabica, Acacia nilotica, Butea
monosperma,Dalbergia sissoo, Terminalia belerica
 Usar land and in moist area: Syzygium cumini, Pongamia pinnata , Tamarindus indica,
Eucalyptus hybrid, Anthocephalus chinenis, Trewia nudiflora
 Some useful grass species are: Eulapliopsis binata,Cenchrus ciliaris, Apluda mutica
Afforestation of salt affected site
Salt-affected soils differ from normal arable soils in respect of two important properties, namely the
amounts of soluble salts and the soil reaction. Excess soluble salts adversely influence soil behavior by
changing its physicochemical properties which in turn have a strong bearing on the activity of plant roots
and growth of plants.
Excess salts may accumulate in the surface horizons of soils mainly due to the following reasons:
 Secondary salinization associated with water logging
 High salt content of Irrigation water
 Release of immobilized salts already precipitated in soils.
 Atmospheric salt dispositions as in coastal areas.
 Weathering of soil minerals.
 Use of fertilizers
The relative significance of each source in contributing soluble salts to the root zone depends on the
natural drainage conditions, soil properties, irrigation water quality, management practices and distance
from the coast line. Soluble salts are either neutral in their reaction (e.g. chlorides and sulfates of sodium,
calcium and magnesium) or are the soda salts (carbonate and bicarbonates of sodium) capable of
producing alkalinity.
Locality Factors:
 Salt-affected soils are generally found in the arid and semi-arid regions of the country.
 Rainfall is often less than 700 mm in the most of these areas and about 80 percent of the annual
precipitation is received during the monsoon season (July to September).
 In the post-monsoon season, water requirement of the transplanted saplings has to be met either
through canal water supplies or through ground water use.
 In the presence of poor quality underground waters salinity problems are further complex
 It has been observed that ground water underneath most saline soils is poor in quality due to excess
of salt load or high sodium adsorption ratio.
 Ground water quality underneath alkali soils is generally good and could be used for irrigation.
Practices for Afforestation
 Creation of favorable root environment for proper establishment of tree saplings on salt affected
soils demands for the adoption of special package of practices.
 For success of afforestation programs following consideration is needed.
 Identification of the nature of salt problem
 Assessment of availability and quality of irrigation water
 Selection of Suitable tree species
 Choice of pitting and planting methods for alkali & saline soils
 Soil and water management

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 Physical and social fencing during initial years
Tree species:
Choice of proper tree species depends upon the local agro-climate, land capability, purpose of planting,
tolerance to salinity/ alkalinity and water logging drought stresses. In general, plantation for fuelwood
are rated better for salty soils than the timber wood tree species.
A short list of consistently better performing species which could be recommended for growing under
saline and alkali conditions of soils.
Acacia nilotica
Butea monosperma
Casuarina equisetifolia
Prosopis juliflora
Prosopis cineraria
Agele marmelos
Emblica officianalis
Grevilia robusta
Psidium guajava
Sesbania sesban
Tamarix articulata
Zizyphus jujuba
Azardirachta indica
Dalbergia sissoo
Punica granatum
Albizzia lebbeck
Cassia siamea
Eucalyptus tereticornis
Pongamia pinnata
Hardwickea binnata
Morus alba
Populus delteoides
Afforestation of water logged area
Water logged conditions are generally met within the high rainfall areas where drainage is poor. Water
logging conditions can be categorized into:
 Water-logging condition caused by stagnant water
 Water-logging caused by impeded but mobile water.
 Swampy areas.
 Marshy areas and saline muddy areas.
Extent of water logged areas is not known. Water logging conditions are also caused by excessive and
faulty canal irrigation in areas adjoining agricultural fields. Such conditions are found in many parts of
Nepal. Water logging conditions are also found in the depressions or borrow pits, along canals, roads,
railway tracks etc.
The lands are fertile with gangetic alluvial deposit, but most of the areas are low lying, a good part of
which remain dry for about eight months, whereas during the monsoon and soon after these areas become
totally submerged by the accumulation of runoff from the surrounding catchment, where the water depth
is upto 5m. Owing to refractory characteristics, these areas become difficult to afforest mainly due to
physiological drought, defective aeration, excessive salt accumulation and poor nutrient availability.
Under natural conditions, nothing grows except tall grasses such as Saccharum spontaneum, Vetiveria
zizanioides Themeda spp, Phagmmites Avistida spp, among the tree species Salix alba, Barringtonia
acutangula, Syzigium cuminii.
Plantation of such lands need special treatments which include, drainage of excessive water, reduction
of excessive salinity and then planting with suitable species.
Choice of species: Trees which have high transpiration rates are preferred for planting in water logged
areas. Some of the species which have given good results are: Eucalyptus robusta, Anthocephalus
chinensis, Syzygium cumini, Salix spp., Terminalia arjuna, Acacia nilotica.spp.

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In marshy areas species such as: Barringtonia acutangula, Lagerstroemia speciosa, Pongamia pinnata,
Casuarina equisetifolia have been found to be successful. Diospyros embryopteris, Pterospermum
acerifolium, Bischofia javanica and canes are generally grown in fresh water swamps.
In terai areas Lagerstroema speciosa and Bishchofia javanica have been successfully grown on water
logged sites where no other species could establish. The soil profiles carrying better growth of
Eucalyptus hybrid possess medium internal drainage while profile with inferior growth are either
associated with rapid to excessive drainage or with impeded drainage leading to pronounced mettling.
Acacia arnesiana
Prosopis juliflora
Parkinsonia
aculeata
Acacia nilotica
Acacia tortillas
Casuarina obesa
Casuarina equisetifolia
Eucalyptus camaldulensis
Feronia limonia
Leucaena leucocephala
Zuziphus jujuba
Casuarina
cunninghamiana
Eucalyptus tereticornis
Terminalia arjuna
Albizzia caribea
Dalbergia sissoo
Pongamia pinnata
Acacia auriculiformis
Acacia deami
Acacia catechu
Szygium cumini
Tamarindus indica
Salix spp.
Afforestation of denuded hills:
Locality factors:
 Soil is usually shallow and stony.
 Infertile soil
 Some places have bare rocks.
 Exposure to sun and drying winds.
 Excessive run-off deficiency of soil moisture.
 Incidence of grazing and illegal felling.
Soil Preparation:
Trenches:
 Contour trenches are usually made on slopes up to 20%
 The trenches may be continuous or interrupted
 The interrupted trenches are better
 The trenches are usually 3m long and 30cm deep.
 Trenches may be 2-4.5m apart depending upon the angle of slope.
Pits or Patches:
 In rocky areas where trenches cannot be made, patches for sowing or pits for planting may be
made without bothering the regular spacing.
Method of Raising:
 Sowing and planting are both suitable
Choice of Species:
 Indigenous, pioneer, non-palatable sp. i.e. Alnus, Pinus in subtropical areas
 Blue pine, Deodar in Temperate areas.
 Acacia, Eucalyptus (dry subtropical).
Tending and protection
 Weeding and clearing frequently required.
 Protection from grazing and browsing animals
Afforestation in cold desert
Locality Factors:

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 Total precipitation usually does not exceed 50mm.
 Soils vary from sand and sandy loam to loams in these regions.
 These are neutral or slightly alkaline in nature.
 There is sever aridity in the region.
 The aridity is of two types; one caused by the low temperature (below O0 C) inhibiting the
absorption of the water by the plant roots and other caused by the dryness of the atmosphere.
 The land is bereft of all vegetation except for isolated, scattered and overgrazed herbaceous
shrub.
 The growing season is limited to 3-5 months falling during hot period.
 Therefore any attempt of growing trees depends upon the availability of moisture
 The growth of the plant has to be slow because of short growing season
 Wind erosion common in these areas.
Soil working:
Soil working should be done during mid-march to mid-April followed by planting during end of April.
Soil working depends upon the types of land. Two types of soil working system is common in these area.
1. Trench-cum pit type and
2. Irrigation cum drainage type
Suitable Species
In areas having slopes and river banks, species such as: Salix alba, Salix fragilis, Populus alba, Populus
ciliata, P. termuloides, P. tremula, P. nigra,p.cadicuas. Among willows, Salix fragilis, S. flabellaris, S
angustifolia are under cultivation. S. hastata, S. wallichiana, S. daphnoides etc. grow naturally.
Other species: Juniperus wallichiana, J. communis etc can also be grown. In marshy areas, with strong
alkalinity pH upto 9.5, pure Salix plantation is suggested.
1.4 Reasons for failure of plantation
Technical Reasons
Plantations may be unsuccessful if the species is planted on the wrong site, unsuitable to climatic and
soil conditions of the locality. Where appropriate and tried technique of establishment is ignored.
 Using of bare rooted stock instead of container raised plants,
 Planting weak and injured plants
 planting at the wrong time when soil moisture has reached the critical level,
 Planting of evergreen forest species in the arid areas planting species of high transpiration rates
in the arid areas or conversely planting arid species in the waterlogged areas.
 Even transportation of seedlings to the dry site, foreseeing rainfall will destroy most of the plants
before actual planting.
 Failures can be avoided if species trails are conducted before large scale plantations are established.
 Correct time of planting is very important as most of the plantations are relied on monsoon.
 To obtain good growth, weeding and hoeing is desirable by removing all competing vegetation.
 All plantations need protection from grazing and fire incidence.
 Proper Supervision
1.5 Selection of planting stock for plantation

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• No species should be selected for planting until its nursery technique, silvicultural requirements
and its influence on the local environment is known.
The plantation should meet the following requirement:
1. Purpose of Plantation: The species should meet the objective for which plantations are raised to play
a role in the economy of the state.
 This demands, therefore, the national and state policy of forestry should be kept in view.
 If a plantation is raised to provide raw materials for an industry, the choice should conform to
the specifications for the industry.
 For creating asset on community land for the local inhabitants, multipurpose species which serve
more than one purpose are require to be selected.
 For growing timber, species worked at large rotations are advisable in the stated forests.
2. Resistance to pests and diseases:
 Under suitable conditions plantations grow in healthy state.
 However attempts to raise the preferred species in plantations may fail if they are grown funder
adverse conditions and in a locality where diseases are present
 To maintain greater flexibility in the matter of selection of site and for fire and pest protection a
mixture of a limited number of species is advisable for industrial plantations.

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Unit 2: Forest Genetics (5)
2.1 Genetic Material, gene expression and interaction, gene techniques
Any material of plant, animal, microbial or other origin that carries genetic information and that passes
it from one generation to the next. The material used to store genetic information in
the nuclei, mitochondria or plastids of an organism's cells; either DNA or RNA.
Forest genetic resources (FGR) are the heritable materials maintained within and among tree and other
woody plant species that are of actual or potential economic, environmental, scientific or societal value.
Importance of forest genetic diversity
They are crucial to the adaptation and protection of our ecosystems, landscapes and production systems,
yet are subject to increasing pressures and unsustainable use. Conservation and sustainable management
of FGR is therefore a must to ensure that present and future generations continue to benefit from forests
and trees.
The contribution of forests and trees to meeting the present and future challenges of food security,
poverty alleviation and sustainable development depends on the availability of rich diversity between
and within tree species.
Genetic diversity is needed in order to ensure that forest trees can survive, adapt and evolve under
changing environmental conditions. It also maintains the vitality of forests and provides resilience to
stresses such as pests and diseases.
Furthermore, genetic diversity is needed for artificial selection, breeding and domestication programmes
for the development of adapted varieties or to strengthen useful traits.
Gene expression and interaction
Gene expression is the process by which information from a gene is used in the synthesis of a
functional gene product.
These products are often proteins, but in non-protein coding genes such as transfer RNA (tRNA) or small
nuclear RNA (snRNA) genes, the product is a functional RNA.
The process of gene expression is used by all known life—eukaryotes (including multicellular
organisms), prokaryotes (bacteria and archaea), and utilized by viruses—to generate
the macromolecular machinery for life.
Several steps in the gene expression process may be modulated, including the transcription, RNA
splicing, translation, and post-translational modification of a protein. Gene regulation gives
the cell control over structure and function, and is the basis for cellular
differentiation, morphogenesis and the versatility and adaptability of any organism.
In genetics, gene expression is the most fundamental level at which the genotype gives rise to
the phenotype, i.e. observable trait. The genetic code stored in DNA is "interpreted" by gene expression,
and the properties of the expression give rise to the organism's phenotype. Such phenotypes are often
expressed by the synthesis of proteins that control the organism's shape, or that act as enzymes catalyzing
specific metabolic pathways characterizing the organism. Regulation of gene expression is thus critical
to an organism's development.

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Gene interaction: In genetics, gene-gene interaction (epistasis) is the effect of one gene on a disease
modified by another gene or several other genes. Biological epistasis, i.e., the gene-gene interaction has
biological basis, is in contrast to statistical epistasis that describes deviation from addition in a linear
statistical model (Gilbert-Diamond & Moore, 2011). Epistasis can be contrasted with dominance, which
is an interaction between alleles at the same gene locus. Gene-gene interaction is a common component
of genetic architecture of human complex diseases; however, it is difficult to detect.
2.2 Hybridization, mutation and polyploidy
Hybridization is the process of an animal or plant breeding with an individual of another species or
variety. In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of
different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always
intermediates between their parents (such as in blending inheritance), but can show hybrid vigour,
sometimes growing larger or taller than either parent.
The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in
the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy,
a key question is how closely related the parent species are.
Hybridization and Introgression
hybridization = F1
“crosses between genetically differentiated taxa”
introgression = F2 backcrosses
“movement of genes between species (or other well-marked genetic populations) mediated by back-
crossing”
Polyploidy is the state of a cell or organism having more than two paired (homologous: having the same
relation, relative position, or structure) sets of chromosomes. Most species whose cells
have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes—one set inherited
from each parent.
Types of polyploidy
Autopolyploidy: more than 2 genetically identical genomes
Allopolyploidy: combines the genomes of more than one species
Intermediate situations, e.g. segmental allopolyploids

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Ancient polyploidy followed by chromosomal re-patterning and restoration of diploid-like chromosome
behavior "diploidization"
Mutation is the changing of the structure of a gene, resulting in a variant form that may be transmitted
to subsequent generations, caused by the alteration of single base units in DNA, or the deletion, insertion,
or rearrangement of larger sections of genes or chromosomes.
• Sudden changes occurring in genetic material is known as mutation.
• The three different kinds of changes in genetic materials can be point mutations, soemantic , and
suppressor mutation. A point mutation or substitution is a genetic mutation where a single nucleotide
base is changed, inserted or deleted from a sequence of DNA or RNA.
• The occurrence of a mutation in the somatic tissue of an organism, resulting in a genetically mosaic
individual.
• Intragenic suppression results from suppressor mutations that occur in the same gene as the
original mutation.
2.3 Speciation
Speciation is the evolutionary process by which populations evolve to become distinct species. 2 patterns
of speciation. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of
lineages, as opposed to anagenesis, phyletic (gradual) evolution within lineages.
Angenesis (gradualism) is the accumulation of
changes in one spp that leads to another species.
It is the lineage of the species. Over time a
species may accumulate enough changes that
differes from ancestral species.
Cladogenesis (branching): is the building of one
or more new species from an ancestral species
that continues to exist.
Charles Darwin was the first to describe the role
of natural selection in speciation in his 1859
book On the Origin of Species. He also
identified sexual selection as a likely
mechanism, but found it problematic. 4
geographic modes of speciation in nature, based
on the extent to which speciating populations are
isolated from one another:
1. allopatric,
2. peripatric,
3. parapatric, and
4. sympatric

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2.4 Population genetics
Population genetics is the study of genetic variation within populations, and involves the examination
and modelling of changes in the frequencies of genes and alleles in populations over space and
time. Population genetics is a subfield of genetics that deals with genetic differences within and
between populations, and is a part of evolutionary biology.
Genetic selection is the process by which certain traits become more prevalent in a species than other
traits. These traits seen in an organism are due to the genes found on their chromosomes.
 Natural selection is the differential survival and reproduction of individuals due to differences
in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of
a population over generations.
 Artificial selection is the identification by humans of desirable traits in plants and animals, and the
steps taken to enhance and perpetuate those traits in future generations.
Migration: In population genetics, gene flow (also known as gene migration or allele flow) is the
transfer of genetic variation from one population to another. If the rate of gene flow is high enough, then
two populations are considered to have equivalent allele frequencies and therefore effectively be a single
population.
The migratory behavior includes a suite of traits that the animals need for travelling between areas of
reproduction and survival. Scientists have found that, at least for some species, a bird's genes dictate the
route it takes when it migrates e.g. Siberian bird.
Genetic drift is a change in allele frequency in a population, due to a random selection of certain genes.
Oftentimes, mutations within the DNA can have no effect on the fitness of an organism. These changes
in genetics can increase or decrease in a population, simply due to chance.
Random drift is caused by recurring small population sizes, severe reductions in population size called
"bottlenecks" and founder events where a new population starts from a small number of individuals.
Evolution is the process by which different kinds of living organism are believed to have developed
from earlier forms during the history of the earth.

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Tree species can be divided into groups based on their evolutionary origins;
1. Holarctic: relating to or denoting a zoogeographical region comprising the Nearctic and
Palaearctic regions combined.
2. Neotropic: relating to or denoting a zoogeographical region comprising Central and South
America, including the tropical southern part of Mexico and the Caribbean. Distinctive animals
include edentates, opossums, marmosets, and tamarins.
3. Paleotropic: The Paleotropical Kingdom (Paleotropis) is a floristic kingdom comprising tropical
areas of Africa, Asia and Oceania (excluding Australia and New Zealand), as proposed by Ronald
Good and Armen Takhtajan.
4. Capensis: The Cape Floristic Region is a floristic region located near the southern tip of South
Africa
2.5 Pollination, problems faced in forest genetics
Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma.
The goal of every living organism, including plants, is to create offspring for the next generation. One
of the ways that plants can produce offspring is by making seeds.
Bees and other insect pollinators are beset by the same environmental challenges as other species,
including habitat loss, degradation, and fragmentation; non-native species and diseases; pollution,
including pesticides; and climate change.
Problem in pollination
1. Habitat Loss, Degradation, and Fragmentation: Much pollinator habitat has been lost to agriculture,
resource extraction, and urban and suburban development. Habitat degradation, the decline in habitat
quality, is another serious concern. Many pollinators are adversely affected when large, intact tracts of
habitat are broken up into smaller, isolated patches by road construction, development, or agriculture.
2. Non-native Species and Diseases: Plants or animals brought here from other places can decrease the
quality of pollinator habitat. When non-native shrubs such as autumn olive and multiflora rose take over
open fields, they crowd out the wildflowers needed by certain butterfly and bee species for pollen, nectar,
or larval food.

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Unit 3: Tree Improvement
3.1 Methods for tree improvement and its application
Tree improvement is the improvement of heritability of desirable features and their economic
importance by breeding and genetic improvement programs. It is the application of genetic principles
to increase the value of tree crops.
Tree improvement produces genetically superior trees which have better growth, tree form, site
adaptability, wood quality, disease resistance, high productivity and product uniformity. Genetically
superior trees are multiplied through techniques based on reproductive characteristics of a species.
In Nepal the Tree Improvement and Silviculture Centre (TISC) has been carrying out tree improvement
programmes like identification and selection of seed stands, Establishment of breeding seed orchard etc.
The Department of Forest Research and Survey (DFRS) has been carrying activities like Genetic
improvement of Chir pine, provenance trials, and mass multiplication of Eucalyptus etc.
Advantage and Limitations of tree improvement
• One major advantage of genetic improvements in forest tree is that once a changes is obtained,
it can be kept over a number of generation.
• The genetic materials that is developed can be kept essentially intact for an indefinite time
through methods of vegetative propagation.
• The size of trees creates problems in measurements, crossing and especially in seed collection.
• Also, related to size is finding suitable areas necessary for “storage” of desired genetic materials
and for testing.
 Availability of seed with the known or desired genetic background is a frequent problem.
 A lack of knowledge about what will be desired in the future.
 And most one problem that was severe in the early years, which is much improved now but
nevertheless is still with us, is the attitude of the foresters themselves.
3.2 Selection, selection methods, selection for several traits, recurrent selection
Selection refers to the identification of the best trees genetically and phenotypically, for the TI
programme.
The methods of selection in an applied tree improvement programme are based on the same general
principle; that is choose the most desirable individuals for use as parents in breeding and production
systems. So the selection of elite and plus tree is crucial.
The objective of selection is to obtain significant amounts of genetic gain as quickly and inexpensively
as possible and to maintain a broad genetic base to ensure future gain.
Species choice, provenance selection and propagation method are the major aspects of tree breeding.
Plus tree selection, progeny testing, provenance test and vegetative propagation have been used since
early of civilization and often regarded as conventional tree breeding techniques while seed orchards,
clonal propagation, somatic embryogenesis, micro-propagation or in-Vitro propagation, and
biotechnology are modern tree breeding techniques.
The method chosen for any particular tree improvement programme depends on the
– Types of genetic variation in the population
– Whether pedigree information exists.
– The degree of urgency in establishing production seed orchards.

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The great variation within the important traits of the most of the trees and their reasonably strong general
combining ability allows a good chance for gain by selecting desired phenotypes.
Some of the selection techniques are:
1. Mass selection-trees selected from plantations based on their phenotypes. Used when the heritage of
the tree is unknown.
2. Family selection-entire families are selected based on their average phenotypic performance.
3. Sib selection-individuals selected on the basis of their siblings. Used when destructive sampling must
be used to measure the trait.
4. Progeny testing-parent trees are selected based on the performance of their progeny.
5. Within family selection-individuals selected on the basis of their deviation from the family mean.
Rarely used.
Selection criteria
Different species have by nature different architecture. Selection traits may vary between different
species and improvement programmes. However, timber species to be cultivated in plantations share a
number of desired features. The ideal plantation tree has following characteristics:
1) Straight, cylindrical, non-forking, non-twisting bole.
2) Fast growth
3) Narrow crown
4) Thin branches with wide branch angles
5) High wood density and long fibers.
6) Resistance to pest and diseases.
7) It should be genetically and phenotypically superior.
8) High yielding, high productive and very good in health.
9) Should be straight, less branching with handsome crown.
10) Should be mature (middle aged), not be stag headed.
11) Vigorous flowering and fruiting
Where to select
Selection is carried out in natural stands or preferably in plantations. Certain considerations of
importance in the choice of the site for selection are identified below:
1) Selection should be made from stands that are as pure in species composition as possible.
2) Selection should be concentrated on stands or plantations that are average or better in traits
of interest.
3) Selection works better in an even aged stand, since the age difference can then be eliminated
from the evaluation.
4) Selection is best carried out in a mature stand, i.e near to maximum height.
5) Selection in natural forests where selective logging has taken place should be avoided since
that may imply that the best trees have been logged, leaving the poorer (genetic material)
behind. Logging may also have influenced crown competition.
Steps in tree selection
1. Mapping of area and stand
– Selected trees will be demarcated on the map.

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– The map is covered with plastic sheets with coordinates to facilitate location and demarcation
of selects.
2. Site description.
– In case of homogenous environment this may be carried out as representative for the whole
area.
– In case of a heterogeneous area, site evaluation is conducted for each selected tree.
3. Selection and marking of trees
– Candidate trees are marked and graded. The mark should be distinct and conspicuous.
– The tree is marked with a number, which corresponds to that in the grading sheet and on the
map.
– Yellow, red or white paint should be used for numbers.
4. Grading of the trees
– The candidate trees are measured and graded against comparison/check trees
– Graded on the basis of height, DBH, crown diameter, bole form, branch angle, branch diameter,
forking, pruning, tree health etc.
Methods of selection:
1. The Regression selection System: The most useful method of tree grading for the uneven aged or
mixed species types. This method requires the development of tables relating the characteristics of
interest to tree age. Quality characteristics can often be determined on the basis of the phenotype of the
candidate tree alone without need for comparison trees.
2. The mother tree system: When there is no immediate urgency to obtain large amounts of improved
seeds. It consists of locating “Good” trees that are usually not as good as select tress in the comparison
tree or regression systems. This method has been used extensively for hardwood for which planting
programmes are small and seed are no immediately needed.
3. The subjective Grading system: Done based only on the judgment of the grader about what constitute
a good tree. This is certainly possible, but the grader must know the species intimately and must be as
unbiased as possible. Successful only if the grader is experienced and dedicated to finding the best trees
possible.
4. Recurrent selection: This techniques permit the elimination of the originally selected and the
incorporation of new selections. The practice is most common in seed orchards for production and
control of development.
3.3 Seed orchards, importance, scope, establishment, management
 Seed orchards are plantations of genetically superior trees, isolated to reduce pollination from
genetically inferior outside sources, and intensively managed to produce seeds
 Established by setting out clones (as grafting or cutting) or seedling progeny of trees selected for
desired characteristics
 Ensures regular supply of trees
 In 1949, first pine seed orchard was planted in Sweden although this concept was applied before
1940 to rubber trees
 Seed Orchard (SO): A plantation area or garden raised/tested specifically for the production of
high quality seeds and in which the seeds are of high quality.

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 Seedling Seed Orchard (SSO): Seed orchard which has been raised from the seedlings from
seeds of plus trees.
 Vegetative/Clonal Seed Orchard (CSO): Seed orchard which has been raised by grafting
clones of the plus tree.
Definition: A seed orchard is a plantation of selected clones or progenies which is isolated or
managed to avoid or reduce pollination from outside sources, and managed to produce frequent,
abundant, and easily harvested crops of seed (Feiberg and Soegaard, 1975).
A seed orchard is an area where seeds are mass-produced to obtain the greatest genetic gain as
quickly and inexpensive as possible (Zobel et al, 1958).
Types of Orchard
1. Clonal seed orchard - Orchard established with vegetative propagules such as grafts, cuttings or
tissue culture raised plantlets. Such orchard established with untested clones is known as first
generation orchard. Clonal orchard developed with genetically tested clones (elite clone) is called
advanced generation orchard.
2. Seedling seed orchard - Orchard established with seedling progeny (half-sib or fullsib) followed
by rouging of inferior families as well as inferior individuals within family.
Both type of orchards are established depending on the facilities, particularly in terms of trained
personnel, and the genetic gain sought by the organization. However, clonal orchards are most
commonly used.
Establishment of Clonal Seed Orchard
Production of clonal material
The production of clonal material is through different vegetative propagation techniques. Commonly
used vegetative propagation techniques are grafting, cutting, air layering, tissue culture etc., in case
of grafting two individuals, rootstock and scion are involved. These may interact positively or
negatively. The selected tree with desired characters is called scion, which donates bud material that
is grafted on rootstock. The selected tree with desired characteristics, which donates bud material, is
also called ortet.
Selection of orchard site and its preparation.
- An area which is easily accessible and near to main/regional station should preferably be selected.
- The selection of site is also influenced by the regional and local seed needs. Nearness to the
center helps in easy monitoring of the programme.
- An area that will not be diverted for some other purpose like construction of road, market, dam,
etc. in future should be selected
- Select orchard site, which favours profuse flowering and fruiting. Favorable conditions are
essential for regular, reliable and higher production of seed.
- Severe drought, wind and frost may all have an adverse effect on the orchard trees particularly
on flowering and seed setting.
- Select an orchard site where problems due to destructive animals are less.
- Poor sites are unsuitable for clonal seed orchard development. Abandoned agricultural lands with
average fertility are the best suited for orchard establishment. Highly fertile land often delays
flowering because of heavy vegetative growth.
- Flat land is highly suitable for orchard development.
- Establish orchard in an area with good drainage.
- Remove all weeds and other bushes.

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- Plough the orchard site and level properly. Gently sloping land needs some sort of soil
conservation measure.
- Fence the area properly before field planting clonal materials.
- Dig pits of optimum size, the size of the pits will vary (0.45 x 0.45 x 0.45 to 0.9 x 0.9x.0.9 m3)
according to the soil type.
- Fill the pits with good soil, sand and FYM in the required proportion. Field plant grafts in a
particular design during rainy season.
- All plants should be labeled with plastic or aluminum tags for proper identification at a later date.
Size of orchard
- The actual size of orchard depends on the total seed or seedling requirement.
- The other factors affecting orchard size are location, importance of the species, availability of
land in a particular locality and facilities.
- In most cases the minimum size of the orchard should be 2.5 to 5 hectare.
- This helps in planting minimum/optimum required number of clones and ramets of each clone to
minimize related mating and also to have broad genetic base.
Clonal placement in seed orchard
- Proper placement of clones in an orchard is highly essential to minimize selfing, relatedness among
progeny and to increase chances of complete mixing.
- The actual spacing between ramets of different clones for most of the tropical species varies from 4
x 4m2 to 8 x 8m2. The spacing also depends on the fertility level of the soil. Good soil promotes
good growth.
Pollen dilution zone
- The orchard should be protected from contamination by outside inferior pollen sources. This can be
achieved either by establishing the orchard on sites where contamination by pollen of the same or
related species is likely to be negligible or by creating a pollen dilution zone at least 100-200 meter
wide.
- The actual distance will depend on the reproductive biology and breeding systems of the species.
Management of Clonal Seed Orchard
- Management procedures should be directed towards early establishment and healthy development of
the clones and the promotion of sustained fruit yield.
- Subsoiling the orchard site to prune surface roots, helps greater root penetration and proliferation,
and reduce surface water runoff. It also helps alleviate conditions of soil compaction.
- Protect the floor of the orchard from wind and water erosion.
- Maintain adequate level of organic matter for proper nutrient. Establish good ground cover to achieve
these objectives. Any leguminous crop which grows fast may be grown.
- Remove weed growth to benefit the tree from fertilization and irrigation.
- Avoid burning and grazing in the orchard as these results in damage to grafts and soil compaction.
- Keep the floor of the orchard leveled and clean for ease of collection of seeds.
- Apply fertilizer to the orchard for promoting growth and vigour of clones when young and to induce
flowering at a later date.
Establishment and Management of Seedling Seed Orchard
• The basic principles and methods of establishment of seedling seed orchard are same as clonal seed
orchard.

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• Collect open pollinated seed (half-sib) from selected plus tree in their original locality or from clones
of these trees assembled in a first generation orchard.
• Maintain identify of seed lots by individual tree/ clone. Each lot will represent a family.
• Raise seedling (progeny) and establish seedling orchard
• The methods remain same except spacing. Use close spacing, say 4 x 4 m2 for teak. This will help
in keeping optimum spacing at a later date when inferior families and inferior individuals within
family are removed on the basis of genetic test results.
• Follow the same methods of maintenance, management, seed harvesting and record keeping as
described in case of clonal seed orchard.
3.4 Vegetative propagation:
• The use of vegetative propagation is rapidly increasing and its vital importance to tree improvement.
• Vegetative propagation has been successfully for several centuries by horticulturists. The older
horticultural practices as well as the new methodology are being increasingly applied in tree
improvement program.
• Vegetative propagation has been employed in forestry for more than 100 years.
Uses of vegetative propagation
breeding orchards.
uation of genotypes and their interaction with the environment through clonal testing.
programs.
Methods of vegetative propagation
A) Propagation by cuttings: Vegetative propagation is commonly carried out from cutting of vegetative
parts of the donor plant. The cuttings of vegetative parts are of three types.
B) Propagation by Layering: In layering adventitious roots are initiated on the stem or branch of a tree,
which after induction of roots is detached and planted or roots a small part of ring of bark is removed.
The area is kept moist by covering it with peat moss, soil etc. and wrapping it with polythene covering
to avoid moisture loss. After some time the roots are produced and at this stage the branch is cut and
planted.
C) Propagation by Grafting: Grafting is a technique of a joining two or more plants species in a manner
that they start growing together and subsequently results in a complete plant. The piece of plant that
contains dormant buds is joined to another piece of plant, which contains its own root. The former is
known as scion and the latter is known rootstock. Scion grows into a shoot system, whereas rootstock
developed into a root system of a grafted tree. Grafting in forestry is done only when the species is
difficult to propagate through cuttings. It is extremely useful in raising clonal seed orchards where
superior clones are grafted on to the local rootstock.
3.5 Plant tissue Culture and gene transformation:
Tissue culture is the newest and currently most publicized of the vegetative propagation method. Tissue
culture has great potential, but it must be view realistically. The uniformity of individuals within clones
of identical genetic makeup are sometime quite dissimilar, often showing as much variability as
seedlings from individual seeds from a given tree.

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The plant tissue culture is defined as a 'technique of growing plant cells, tissues or organs in an artificially
prepared nutrient medium under an aseptic condition in the laboratory'.
It is especially important to produce plantlets that are essentially uniform within a clone before tissue
culture will be of value for operational plantings. This is the cause because plant uniformity is one of the
major attraction of vegetative propagation. The best immediate use for tissue culture will be as a rapid
method of utilizing improved genetic stock. And major job will be make the system cost effective.
Plant tissue culture and gene transformation:
– Restricing the genetic base and monoculture
– Restricting the genetic Base
– Dangers of a restricted genetic base
Shoot Culture
shoots can be used as explants for Tissue Culture.
Callus Culture
lets can be obtained from callus.
solidified
culture medium
of plants can be obtained in a short period of time
Meristem Culture
the laboratory.
Embryo Culture
Role of Plant Tissue Culture in Plant Improvement
• Tissue culture technique helps to propagate plants of economic importance such as orchids,
vegetable, medicinal plants etc.
• Tissue culture technique helps to propagate virus free plants.
• In-vitro propagation is a powerful and attractive tool for the rapid cloning of desirable plants. In
tissue culture plant multiplications can continue throughout the year irrespective of the season.
• It has great value as a potential system of germplasm storage.

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Unit 4: Interaction of Site Factors (5)
4.1 Liebig’s law of minimum:
This “law” or “principle” of the minimum was formulated by Carl Sprengel, a German botanist, as early
as 1828.
Liebig’s work became the foundation for laboratory oriented teaching as it’s known today and earned
him consideration as the “Father of the fertilizer industry”.

25
Simply put, Liebig’s Law of The Minimum summarizes that “plant growth and health is not
controlled by the total amount of nutrients available in the soil. But instead plant growth and
health is controlled by the scarcest of the nutrients available in the soil”.
Thus, the concept first stated by J. Von Liebig in 1840, that the rate of growth of a plant, the size to
which it grows, and its overall health depend on the amount of the scarcest of its essential nutrients that
is available to it. He observed that yield of crops was often limited not by the nutrients needed in large
quantities, such as CO2 and water, since these were abundant in the environment but by some factor
needed in small quantity, e.g. zinc or copper, but deficient in the soil
According to him, growth of plants is dependent on the amount of food stuff which is presented to it in
minimum quantity. It is known as “Liebig’s law of the minimum”
There are two important considerations in this principle:
1) That Liebig’s law is strictly applicable under steady state conditions, i.e. no change in other
factors takes place and
2) That high concentration or greater availability of some factors may modify the utilization of
the later
For example, some plants have shown less zinc requirements, when grown under shade than when
growing under full sun-light. In some plants, abundant supply of magnesium in the soil compensates the
requirement of calcium. This is called factor interaction.
4.2 Shelford’s law of tolerance
• Shelford's law of tolerance is a principle developed by American zoologist Victor Ernest
Shelford in 1911.
• He explained that not only too little or the minimum of some substance is a limiting factor, but also
too much of some factors e.g. heat, light, water, etc. can be limiting factors
• According to him, all organisms, plants and animals have an ecological minimum and maximum.
• This range between minimum and maximum represents the limits of tolerance and the principle is
called limits of tolerance principle also called Shelford’s law of tolerance.
Salient features of Shelford's law of tolerance
1. Plant may have a wide range of tolerance for one factor and narrow range of tolerance for another

26
2. Plants with wide range of tolerance for all factors are likely to be most widely distributed. For
e.g. Lantana camera appears to have a wider range of tolerance for all factors than other shrubs.
3. When conditions are not optimum for species with respect to a single ecological factor, the limits
of tolerance may be reduced for another factor. For e.g. when soil nitrogen is deficient and is
limiting factor, the resistance of grasses to drought is reduced
4. Reproduction is usually a critical period when environmental factors are most likely to be
limiting. The limits of tolerance for reproductive individuals are usually narrower than for non-
reproducing adult plants.
4.3 Principle of Dynamism and Principle of Thermodynamics
Principle of Dynamism
• Many ecologists believe that the environment and the organism are dynamic
• The changes may be short term or long term
• Studies conducted in several ecosystem on the effect of stress factors generally resulted in three kinds
of behavior
i. Many species were replaced by other set of species
ii. Some species persisted by altering the rate of physiological processes in keeping with the
changes in the environment
iii. Some species or individuals show resistance to the stress factors
Principle of Thermodynamics
• The principle of Thermodynamics are applicable in case of plant life also
• The birth, growth and reproduction of an organism are the functions of energy changes.
The first law of Thermodynamics called “Law of Conservation of Energy” states that “energy is neither
created nor destroyed”, it may change form, pass from one place to another.
• The first law can be seen operational in living system
• The energy from the sun is absorbed by the green plants. The radiation energy from the sun is first
converted to electrical energy (energy of agitated electrons) in the chlorophyll molecules
The electrical energy is converted to chemical energy by the synthesis of complex molecules. When the
complex molecules are broken down the kinetic energy changes take place in the living systems
exemplifying the operation of the first law of Thermodynamics
The second law of Thermodynamics is also operational in living system which says that whenever
energy is transformed from one kind to another, there is an increase in the eutrophy and decrease in the
amount of useful energy.
When radiant energy is transferred in form of food from one organism to another, a large part of the
energy is degraded as heat and a net increase in the disorder of energy and the remainder is stored in
living tissues
4.4 Combined concept and vegetation
Liebig’s law of minimum, Shelford’s law of tolerance and principle of dynamism when combined
together, one arrives at more general concept of limiting factors. In nature, the growth and distribution
of plants are controlled by three factors:
i. The quantity and variability of materials for which there is a minimum requirements and
physical factors which are critical
ii. The limits of tolerance of the organisms themselves to these and other components of the
environment and

27
iii. The adaptability and the resistance the individuals/species are able to develop with
environmental factors (light, temperature, water, air, soil)
• Site factors include all physical and biological factors of an area which determine the occurrence,
distribution and growth of vegetation
• Important site factors are climatic, edaphic, physiographic and biotic.
• All these site factors are very important and are very effective
• Physiographic factor modify the climatic and soil factors
• The climate is perhaps the most important site factor
• Among the climatic factors, the precipitation and temperature are the most effective factors
• According to precipitation and temperature, the major form of vegetation or forest type develop
• Edaphic factors are also dependent to a large extent on the climatic factors (For e.g. development of
soil depends upon the climate to a great extent)
• Precipitation provides soil water without which perhaps no or very little chemical or biological
activities are possible.
4.5 Modification of site factors through silvicultural practice
Several site factors, e.g. light, temperature, soil moisture, water table, soil surface cover, rate of
decomposition or organic matter and several biotic factors can be modified to some extent by
silvicultural practices.
Soil moisture: Conservation and efficient utilization of soil moisture is perhaps one of the most
important silvicultural conditions particularly in arid and semi-arid areas. Proper stand density and stand
composition may be required for soil conservation. Deciduous nature of species economize the use of
moisture and therefore, such species may be given preference. Drought resistant species may be
preferred for plantation in dry areas.
In water-logged areas or in areas where water table is high, heavy thinning and clear-felling need to be
avoided. It has been reported that clear felling leads to rise in water level to the extent of 30 cm to 60 cm
(Wilde et al., 1953). Such rise in water table may convert imperfectly drained soils into poorly drained
or water logged conditions.
Light demanding species require more openings than shade bearers. In evergreen and semi-evergreen
forests, where dense vegetation occurs, manipulation of top, middle and understory vegetation is required
so that light becomes available to the ground. Under dense shade, light intensity may be less than one
percent (Champion and Seth, 1968). Competition is also so intense. In order to induce regeneration of
desired species, manipulation of under, middle and top canopies is very essential.
Temperature: Gradual opening of vegetation in top, middle and under-storey improves light and
temperature conditions. Increase in temperature may enhance the rate of decomposition of organic
matter. Light grazing helps in mixing organic matter with mineral soil.
Controlled burning is one of the important silvicultural tool in the hands of foresters. It can be helpful
in inducing regeneration by reducing competition and creating hygienic conditions. However, adverse
effects of over-grazing and uncontrolled fire are very serious as they threaten the very existence of
forests. Other biotic factors e.g. insect pests and diseases also need to be checked
Thinning, weeding, cleaning, etc. are some of the silvicultural practices which are aimed to avoid
competition in forest resulting in better growth and form of crop. Thinning helps to increase the growth
of remaining trees. Weeds unnecessary compete with seedlings and saplings of tree species and weeding
the site helps in proper growth of trees.

28
Unit 5: Influences of Forests on their environment (6)
Reaction between forest and environment -------- PRODUCTS
Influence of forest to environment – due to
1. Tree canopies
• Intercepts sun rays and precipitation
• Retards velocity of wind
2. Litter falls- Influence soil and water properties
3. Rooting system of trees
• Binds soil
• Nutrient dynamics
Forest and Climate
• Climate is the description in terms of the mean and variability of atmospheric variables such as
temperature, precipitation and wind.
• Climate can thus be viewed as a synthesis or aggregate of weather.
• Climate is thus now more and more frequently defined in a wider sense as the statistical description
of the climate system.
Analysis of the behaviour of components
1. Atmosphere (the gaseous envelope surrounding the Earth)
2. Hydrosphere (liquid water, ocean, lakes, underground water)
3. Cryosphere (solid water, i.e. sea ice, glaciers, ice sheets, etc)
4. Biosphere (all the living organisms)
5. Lithosphere ( upper layer of earth crust )
Forests Influence on Geomorphology
• The roots of trees hold the soil, preventing erosion or landslides
• Depending on species, trees spread their roots into the ground vertically or horizontally
• In this way, the soil between roots becomes more compact, strongly fixed in place
Forests’ Influence on atmospheric factors
• Forests reduce heat in summer and balance in winter
• Forest increases air humidity and keep moisture
• Forest reduces water evaporation
• Forest increases precipitations
• Forest reduces wind velocity
Forests Influence on Soils
• Decomposed leaves in the forest makes the soil better
• Hosts several microorganisms
• Provide nutrients – after decomposition
• Leachates and root exudates add nutrients to soil
Forests support people
• Forest support the livelihoods of more than a billion people living in extreme poverty worldwide

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• Forest provide employment for over 100 million people
• They are home to more than 80 percent of the world’s terrestrial biodiversity
• They help to protect watersheds that are critical for the supply of clean water to most of humanity
Climate change, however, poses enormous challenges for forests and people. Accumulating evidence
suggests that the global climate (i.e. conditions measured over 30 years or longer) is now changing as a
result of human activities mainly: Temperature rise and changed patterns of precipitation.
Estimation: global temperatures would be likely to rise between 1.4 and 5.8 degree C from 1990 to 2100
Forest and Global Warming
• Increase in emission of green house gases in atmosphere
• CO2, CH4, Nox, Ozone, CO, CFCs
• 0.7°C to 2°C increase in temperature during last century
• Temperature increase rate = 0.5°C every decade
How forest releases GHG
• Forest degradation and deforestation
• Forest fire and biomass burning
• Decay of forest organic matter
• Decomposition of organic material - by ‘organic carbon-consuming’ heterotrophic
microorganisms
• They utilize the carbon of either plant/animal or microbial origin as a substrate for metabolism
• Some amount is retained in their biomass OR release as CO2 back to the atmosphere.
Effect of greenhouse gases
• Higher surface and atmospheric temperature
• Reduction if fresh water availability
• Widespread runoff and erosion
• Rising sea level
• Glacial melting
• High evapotranspiration – high precipitation
• Some regions experience low precipitation
• Decrease in soil moisture
• Increase of storm and hurricanes
• Global warming ---- affect every aspect of human life: Natural ecosystems, Biodiversity
• Effect on agriculture ---- Food security, Water availability, Human health,
• Rising Sea Level
• Inundation – loss of human habitation
• Coastline erosion
• Loss of wetland lives
• Infrastructure damage
• Salt penetration in fresh water ecosystems
• Devastation in coastal ecosystem
Prevention measures
• Maintain pasture and grass land
• Reduce frequency and amount consumption of forest biomass by burning
• Decrease forest consumption
• Decrease activities of developmental projects – Environmental planning and Management

30
• Improve efficiency of biomass/fuel combustion in industries/cooking
• Maintain Sinks of Greenhouse gases
- Conserve standing primary and old growth forest as stock of biomass
- Reduce destructive logging – Natural forest management systems or Sustainable harvesting
- Increase harvest efficiency – Harvest species with less damage to standing trees
• Expand sinks of greenhouse gases
- Improve forest productivity on existing forest – Management & Biotechnology
- Establish plantations – croplands/abandoned land
- Restore degraded forest through natural regeneration
- Expand agroforestry
- Increase soil carbon storage – leaving slash after harvest
• Sustainable agriculture technologies
• Expanding afforestation and reforestation
• Prevent conversion of forest for cash crops and developmental project
- Restriction of transfer of forest land for non-forestry purpose
- Special provisions in the Forest conservation Acts
- Developmental projects – controlled through proper environmental planning and management
- Conservation of existing forest through sustainable management
• Productivity of existing forest must be enhanced
• New forest should be created on large scale
• Various measures for protection and conservation of existing forests
Nepal
• The annual deforestation rate was estimated to be 1.7% during the 1980s to mid-1990 s (DFRS,
1999) and 1.8 % between 1980 and 2000 (UNEP, 2001)
• Between 1947 and 1980, where Nepal’s forest cover declined at an annual rate of 2.7%
• Total forest area in Churia decreased by loss of 38,051 ha forest over the period of 15 years (1995-
2010)
Forest and local temperature
• Forest has moderate influence on air temperature
• Several studies confirm that the forest reduces air temperature
• The influence depends on the Density and type of forest
• Study of Zon (1927) – data from 5 European countries - The forests lowered the temperature by
3.91 ° F
• Forests but raise winter temperature slightly
• Forest also reduces the daily range of variation in temperature
• Dense evergreen forests are likely to have more influence on air temperature than deciduous
forest
• Significance of reduction in temperature by forest
Forest and Wind
• Forest offer mechanical obstruction and deflect upwards a large part of moving mass of air
• Forest slow down the velocity of air which enters into the forest
• Dense forest with heavy foliage have the greatest effect
• In a good forest stand wind velocity may be 20-60 % of the open areas
Forest and Frost
• Forest has moderating influence on air temperature

31
• The forest also do not allow temperature to fall down considerably to cause frost
• In open area – frost occurs – damage
• Forest litter on the soil surface provides insulating effect on the soil surface
• Forest decreases occurrence of frost due to Prevention of heavy cold air to descend down to
ground level
• Very little temperature inversion
• Insulating effect of litter prevents the escape of warmth from ground
Forest and Snow Fall
• Forest has effect on snowfall and snow melting
• Forest area has twice snow-water than the deforested areas
• Forest delays snow melting – effect depends on forest type and density and snowfall incident
• Denser the forest – more is the delay
• Coniferous forest are more effective than broad leaved forests
Forest and Evapotranspiration
• Reduce soil evaporation
• Forest affect solar radiation = reduce soil evaporation -Forest shade
• Tree transpiration --- Moisture --- low evaporation
• Annual evapotranspiration in Eucalyptus globulus plantation in Nilgiri hill india – 3475 tons per
hectare which equals to 38% of total rainfall in the area
• Total evapotranspiration losses from forest is always higher than other landuses
• Greater infiltration
• Larger water holding capacity
• Bigger underground reservoir
• More proportion of rainfall enter the forest soil
Forest and Humidity
• The relative humidity is the percent of saturation humidity
• Forest – High Relative Humidity Open area = Low Relative Humidity
• Relative humidity is 3-12% higher in the forest than open area (Zon, 1927)
• Relative humidity was decreased in Ranchi plateau by 5.8 % after deforestation
• The effect vary with Forest types, density, foliage
• The forest soil acts like a sponge and is able to hold a lot of water
• Inside the soil the water is distributed over a network, or in the root canals of the trees
• Water vapor from the forest floor is hold underneath the trees, which makes steamy and foggy
– High humidity
(Refer the notes of Advance Ecology, Unit 5)

32
Unit 6: Hardiness and Tolerance (4)
• Hardiness of plants describes their ability to survive adverse growing conditions.
• Normal condition of soil, air and water provide suitable environment for the growth of most of the plants.
• However there are large areas where normal conditions of climate and soil do not exist and therefore ,
only such plants are able to grow which are either able to adapt to these situation or develop resistance
to these conditions.
Hardiness of a plant is usually divided into two categories: tender, and hardy. Tender plants are those
killed by freezing temperatures, while hardy plants survive freezing—at least down to certain
temperatures, depending on the plant.
"Half-hardy" is a term used sometimes in horticulture to describe bedding plants which are sown in heat
in winter or early spring, and planted outside after all danger of frost has passed.
6.1 Drought Condition
Drought condition refers to the shortage of moisture. This shortage may be due to the low rainfall.
Several plant species growing in such areas are able to develop resistance to drought conditions due to
some adaptations. Roots of the trees absorb moisture from the soil. In soil water is present mostly in
three forms:
1. Gravitational water
2. Capillary water and
3. Hygroscopic water
Tree roots absorb moisture mostly from capillary water. Gravitational water rapidly moves downwards
and roots are not able to utilize it. The hygroscopic water is too tightly held by the soil and roots are not
able to absorb it. Whenever the water potential of the soil falls to a low value it becomes more difficult
for plants to absorb water and are in danger of desiccation.
This problem arise with saline soil (where high salt levels lower soil water potential), frozen soils and
the dry soils of deserts. Under all such situations special features have evolved that allow plants to
survive.
Among the plants that cannot tolerate extreme desiccation but grow in a very dry places, the following
three different types of survival can be distinguished.
6.2 Water tappers
• Some plants develop remarkably long root and are able to tap water supplies from deep ground water.
These plants are called pharatophytes.
• Such plants grow on sand dunes and desert conditions.
• Such tappers are also characteristic of dried up river beds in deserts, where the roots of trees go
straight down upto a depth of 30 meters before branching in moisture soil.
• Often these plants have no special adaption that reduce water loss by shoots, but part of the root
passes through very dry soil is usually covered with waterproof corky layer that restricts the water
loss.
• Must of the perennial plants have deep roots which are able to tap permanent or semi-permanent
ground water resources i.e. Acacia nilotica, A. senegal, Prosopis cineria, P. juliflora, Azadirachta
indica.
• Remarkable records of maximum rooting depths are available for desert phreatophyte.
• Prosopis glandulosa in Arizona has been found to send its root as deep as 53 meters.
• Zizyphus lotus in Morocco has been reported to have roots reaching upto 60 m in depth.

33
Water savers
All vascular plants are to some extent water savers simply by virtue of having a water proof cuticle, but
the species that grow in very dry habitats are known as xerophytes. Following are the adaptations
observed in the plants growing in dry conditions.
1. Ability to close the stomata rapidly and completely: Before the cells are damaged by desiccation,
several species are able to close their stomata opening. Non xerophytes are quite often incapable of
complete stomata closure and respond sluggishly to a fall in leaf water potential.
2. Ability to osmoregulate and possession of high osmotic pressure: As soil dries out water potential
decrease (become more negative) and hydraulic resistance increases. Both these factors reduces the water
uptake into roots and the only way by which plants can compensate for this is that water potential of the
root must decrease. In drying soil, osmotic adjustments occur by an increase in osmotic pressure, partly
by enhanced accumulation of inorganic ions and partly by increasing the level of organic solutes.
Such osmotic adjustments or osmoregulation can occur without any fall in root turgor, which is important
driving force for cell elongation and division and therefore, root growth.
3. Thick and highly water proof cuticle: Xerophytic plants develop highly water proof cuticle, often
covered by waxy or resinous layers
Cuticle resistance to vapour loss is 4-5 times higher in such plants as compared with non- xerophytic
plants. CAM plants (mostly belong to family Crassulaceae) open their stomata in night and close during
day time, hence reduce the water loss.
4. Mechanism that reduces transpiration losses: Reduction in transpiration rate is achieved mainly
through modification that reduces leaf to air temperature gradient. Small leaves such as Acacias dissipate
heat more readily and more easily cooled by convection currents than larger leaves. Hence small leaves
are commonly seen among xerophytes.
Leaves aligned parallel to the sun rays absorb less radiations and similarly leaves with pale and shiny
surface (Atriplex). Another mechanism that effectively reduce transpiration is the release of volatile oils,
producing the aromatic smell typical of Eucalyptus and many Mediterranean species. The oil present
increases the average density of gas in boundary layer and this slows down the rate at which water vapour
diffuses across, just as if air humidity has increased.
5. Sunken stomata: Stomata are deeply sunken in pits below the leaf surface, creating still air conditions
above and reduces water loss. Many xerophytes have stomata confined to lower surface and when leaf
turgor fall sufficiently , the leaf rolls up enclosing the stomata in protected , humid chamber. Sunken
stomata also decrease the temperature gradient and as a result decreases water loss.
A sunken stomata is a stomata in a small pit, which protects the escaping water vapor from air currents,
decreasing water loss from the leaf. Sunken stomata are commonly found in plants in arid environments
as one of their adaptations to preserve water.
Water storers:
Succulent plants such as cacti and Euphorbias are the examples of this group. Succulent plant s strategy
for adapting to drought can be summarized as below:
a. Extensive shallow rots absorb surface water efficiently, even heavy dew is utilized and must of the
water taken up is stored.
b. This storage is possible because losses through transpiration are very low. Cuticle is extremely thick
stomata are few in number often deeply sunken and above all open only during night.

34
c. As external water become scarce, roots wither and stomata remains open for shorter and shorter
periods, eventually closed altogether. Succulents than survive by recycling respiratory Co2 and their
thick cuticle prevent virtually all water loss.
6.3 High temperature
• High temperature is very harmful to plants.
• All physiological activities in plants take place within an optimum range of temperature.
• When temperature increases above this range, all physiological activities are adversely affected and
when temperature increases further, plants die.
• Ability to resist and adopt high temperature varies greatly from plant to plant.
• There are some plants which die when they are exposed to temperature above 350c.
• For most of the higher plants the critical limit of higher temperature lies between 50 C to 60 C.
• High temperature causes coagulation of protoplasmic proteins at high temperature.
• With increase in temperature beyond the optimum range, rate of photosynthesis decreases but rate
of respiration increases.
• Therefore plant is starved and becomes susceptible to attack by pathogen.
6.4 High salt concentration
This situation occurs when soil solution has chlorides, sulphates, carbonates and bicarbonates of calcium,
magnesium, potassium and presence of sodium. Saline soil have salt percentage more than 0.15 percent
and conductivity of saturation extract is more than 4 milli mhos/cm. The pH of such soil is generally less
than 8.5. If the sodium percent is more than 15 then pH of the soil rises more than 8.5.
Depending on their response to salinity, plants can be grouped into two broad classes.
1. Some plants can grow in the presence of high salt concentration. Some time as much as 20
percent, these are called halophytes. These plants develop specially morphological, anatomical,
and physiological characteristics to survive in such conditions.
2. The other class of plants called glycophytes, cannot grow if salt concentration reaches more than
1-2percent in the soil solution.
Salinity adversely affects plant growth because of the following two reasons:
• Osmotic effect
• Ionic effect
Presence of excess salts in the soil solution increase in the osmotic pressure which result in low gradient
between diffusion pressure deficit of the soil solution and that of roots. This makes the absorption of the
water by the roots more difficult, as a result plants suffer from water deficit. This is known as osmotic
stress or physiological stress. This drought is not due to non-availability of water but due to inability of
plants to absorb water.
Under saline conditions, the chlorides and sulphates of sodium and magnesium are present in excess and
plants absorb these ion in large quantities. The presence of excess of sodium and chloride ions cause
toxicity to the plant. Due to the excess of sodium and chloride ions, synthesis of protein and nucleic acid
is reduced. The growth of roots and shoots is adversely affected.
Halophytes have various resistance mechanisms which may be operative in different plants. Some of
these mechanisms are as follows:
• Pumping of excess of ions out of the roots. In this process membrane bound proteins are involved.
• Storing the excess of salts, sometimes converted to a non-toxic form, in the vacuoles.
• Secreting excess ions on to the surface of leaves.

35
Unit 7: Silvicultural System (6)
7.1 Silvicultural systems
Silviculture: The art and science of reproducing and growing trees and forests in a sustainable manner
based on principles of forest ecology for the benefit of society
Silvicultural systems are: The processes by which the crops that constitute a forest are tended, removed
and replaced by new crops, resulting in the production of woods of a distinctive form.
Name of a system is based on:
• number of age classes (e.g. even-aged, uneven-aged), or
• regeneration method (e.g. shelterwood, selection)
A silvicultural system involves:
• method of regeneration (e.g. coppice, planting, natural regeneration, direct seeding)
• form of the crop produced (e.g. “regular” or “irregular”)
• arrangement of the crops over the forest (a form of “normality” usually aimed at)
• The objective of a silvicultural system is to permit the harvesting of a mature timber crop while
providing space for the regeneration of the forest.
• Silvicultural systems are long-range harvest and management schemes designed to optimize the
growth, regeneration, and administrative management of particular forest types for a sustained
yield
Classification of Silvicultural Systems
Silvicultural systems have been classified in a variety of ways; The most commonly used classification is
based primarily on the mode of regeneration. It is further classified according to the pattern of felling carried
out in the forest crop
According to the method of regeneration silvicultural systems are of following two types:
A. High forest systems:
Those silvicultural systems in which the regeneration is normally of seedling origin, either natural or
artificial or a combination of both and the rotation is generally long.
B. Coppice system:
Those silvicultural systems in which the crop originates mainly from coppice and the rotation is short. The
high forest systems and coppice systems are further classified on the basis of pattern of felling and mode
of regeneration as well. A schematic classification of these systems is given here.
Coppice System (Low Forest System)
a. Simple Coppice System.
b. The Coppice of Two Rotation System.
c. The Shelterwood Coppice System.
d. The Coppice with Standards System.
e. The Coppice with Reserves System.
f. The Coppice Selection System.
g. The Pollarding

36
MAJOR SILVICULTURAL SYSTEMS
A. High Forest Systems:
1. The clear felling system:
The clear felling system is defined as a silvicultural system in which equal or equi- productive areas of
mature crop are successively clear-felled in one operation to be regenerated most frequently, artificially
but sometimes naturally also.
The area to be clear-felled each year in uniformly productive sites is l/n of the total area allotted to this
system.
N = no of years in the rotation and is usually referred to annual coupe.
The coupes to be felled every year are made equi-productive.
Removal or felling of mature crop:
According to definition, the entire crop of the coupe should be felled and removed in one operation but
in practices following variations are observed.
1. Retention of some mature trees as frost protection measures or as an insurance against failure or as
nurse crop to facilitate establishment of forest tender species.
2. Retention of promising groups of saplings and poles to prevent unnecessary sacrifice of immature
crop of the desired species.
3. Isolated saplings and poles are ordinarily not retained as they may develop in to wolf trees.
Methods of obtaining regeneration:
The area can be regenerated sometimes naturally but mostly artificially
Artificial regeneration is preferred due to following reasons
1. It is the surest and quickest method of improving crop composition.
2. It facilities introduction of fast growing and high yielding exotics.
3. It provides better financial returns.
4. The regeneration is established sooner, so the area can be opened for grazing sooner.
Advantages:
1. It is simplest of all high forest system. It does not require a high degree of skill.
2. As felling is concentrated, the yield per unit area is more and consequently the cost of felling and
extraction is low.
3. Introducing fast growing exotics and regulating composition of new crop through artificial
regeneration is advantageous.
4. It makes the supervision of all operations easy.
5. There is no damage to new crop by felling.
6. If properly tended the even aged crop produced have trees with cleaner and more cylindrical
boles.
7. Entire crop is regenerated in one operation. Its establishment is quicker there by reducing the cost
and rotation.
8. As the regeneration establishes early, the coupe can be opened up for grazing soon.
9. The distribution of age class is very regular.
10. The success or failure of regeneration is clear by the end of first year or in few years.
Disadvantages:
1. It is the most artificial system.

37
2. Soil remain open there is more danger of soil deterioration and erosion
3. The danger of weeds and grass invasion increases.
4. It produces even aged crop, which is less resistant to damage by wind.
5. when the crop is pure it becomes more susceptible to damage by Insects, plant parasites and
pathogens.
6. It sacrifices all immature crops that may still be putting on valuable increment.
7. Growing space and site factors are not fully utilized.
8. Annual yield is less than uneven aged crops.
9. This system is not suitable on hilly area and slopes.
10. The system is aesthetically very bad.
2. Seed Tree Method
In this method the stand is clear felled except for a few seed trees, which are left standing singly or in
groups to produce seeds for regeneration
After a new crop is established these seed trees may be removed or left indefinitely.
The chief distinction from shelter wood system is that the seed trees are retained only for seed production
and not enough to provide shelter.
On the basis of arrangements of seed trees the seed tree methods may be:
• Single Tree Method.
• Group Tree Method
• Strips or Rows Method
Characteristic of Seed Trees.
1. Wind firmness: Trees with tapering boles are more resistant to wind.
2. Seed producing ability: The best trees are members of Dominant crown class having wide deep
crowns and relatively large live crown ratio.
3. Age: Seed tree must be old enough to produce abundant fertile seeds, The age at which seed
bearing begins in closed stand is the safest criteria.
Number and Distribution of Seed Trees: It depends on following factors
• Amount of seed produced/tree
• The no. of seed required
• Seed Dissemination
• Number of viable seed produced (depend on pollination. There will be low no of viable seed in
isolated trees
• Seed germination
• Seedling establishment
Advantage: Ample opportunity for Phenotypic Selection, suitable for Light demanding species.
Disadvantage: Under stocking, over stocking, damage by forest and drought.
3. Shelterwood Systems
Shelterwood system is a silvicultural systems in which the over wood is removed gradually in two or
more successive felling depending on the progress of regeneration.
In other words, the shelter wood system involves gradual removal of the entire stand in two or more
successive felling extending over a part of the rotation.
The trees, which are no longer capable of increment in value, are removed to make room for regeneration
to come in

38
The trees, which are growing vigorously, are retained to provide
(a) Shelter
(b) Seed
(c) Rapid diameter increment and value increment
(d) Protection of site against deterioration.
Kinds of Shelterwood system:
The varying patterns of regeneration felling and their distribution in space and time, results in a variety
of shelterwood systems.
Uniform shelterwood system: Regeneration felling is done by making uniform opening
Group shelterwood system: Regeneration felling is done in scattered groups
The shelterwood strip system: Regeneration felling is done in strips
Irregular Shelterwood System: Opening is made irregularly. Uneven aged crop is produced. There is a
compromise between shelterwood group system & selection system
Indian irregular shelterwood system: Uneven aged crop is produced and immature trees are retained
as future crop. It is a compromise between Uniform System and Selection System.
One cut sheltered: Removal of over wood in one operation if sufficient advance growth is present
Uniform Shelterwood System (Uniform System)
The canopy is uniformly opened up over the whole are of a compartment to obtain uniform regeneration.
It is also called as shelterwood compartment system or compartment system.
Pattern of felling:
Preparatory felling: It is a felling made under a high forest system with the object of creating conditions
favorable to seed production and natural regeneration
 Create gaps in the canopy
 Create favorable conditions on the forest floor.
Seeding felling: It is defined as opening the canopy of a mature stand to provide conditions securing
regeneration from the seed of trees retained
This is the first stage of regeneration felling and the object is to make opening in the canopy all over the
compartment so that favorable conditions are created for regeneration.
There are two important considerations
1. Selection of trees to be retained:
 Genetically superior trees.
 The number of trees varies according to the silvicultural requirement of species.
 The shade bearing sp. and those with heavy seed-retain more seed trees (small opening)
 The light demanding sp. and those with light seed-retain less seed trees (large opening)
 For the same sp. opening is lighter in the drier areas than in moist areas.
 Seeding felling is done with caution if there is danger of invasion of grasses and weeds.
 Large no. of seed bearers on southern aspect and less no. of seed bearers on northern aspect
for the same species.
2.The number of seed bearers:
The number of seed bearers to be retained depends on:
 Seed requirement of the area.
 Amount of light to be admitted (shelter)

39
 Moisture condition
 Condition of weed growth
 Altitude and aspect.
Examples:
Species No. of seed bearers Approx. Distance between trees
Pinus roxburghii 12-18 on cooler aspect 24-30m.
20-25 on warmer aspect 20-22m.
Pinus wallichiana 25-30 18-20m.
Cedrus deodara (Deodar) 45-50 14-15m.
Picea smithiana (Spruces) 45-50 14-15m.
Abies pindrow (Fir) 75-87 11-12m
Secondary felling: It is defined as a regeneration felling carried out between seeding felling and final
felling in order gradually to remove the shelter and admit increasing light to the regenerated crop
Removal of trees in secondary felling depends on progress of regeneration and its light requirement. It
also helps in the manipulation of mixture of crop.
Final felling: It is defined as the removal of the last shelter or seed trees after regeneration has been
affected. It is the final stage in regeneration felling when there is completely stocked with established
regeneration which do not require shelter.
Advantages:
1. Marking and felling of trees of the over wood are simpler than in other shelterwood systems as well
as selection system.
2. In this system the soil is not completely denuded so there is little risk of soil deterioration and erosion.
3. As the regeneration operations are carried out under the shelter of older crop, there is little danger of
invasion of the area by weeds and grasses.
4. The young crop is protected against adverse climatic factors such as cold, frost, winds, drought etc.
5. As the regeneration is obtained from seeds obtained from best selected trees, the new crop is superior.
6. It is a suitable system for the regeneration of both light demander and shade bearer species. In mixed
forest it is suitable to regenerate a mixture of different species by regulating of light reaching on
forest floor.
7. As the new crop appears before the old one is harvested, the average length of rotation is shortened.
8. The growing space is more fully utilized as the regeneration grows under the shelter of older trees.
9. It makes supervision and control of various operations easy.
10. From aesthetic point of view the system is superior to clear felling system.
Disadvantages:
1. As the over wood is removed in more than one operation there is much damage to the young crop.
2. In mixed forest with species having different light requirement, the manipulation of canopy requires
skill and knowledge of silvicultural requirement of species composing the mixture.
3. The isolated seed bearers are susceptible to wind damage.
4. In the species having long intervals between seed years, after seeding felling there may be invasion
by weeds and regeneration may be affected.
5. In species with longer regeneration period, weeding and cleaning has to be done for longer period
and the natural regeneration becomes costly.

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