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    Mini literature review exercise Mini literature review exercise Document Transcript

    • A MINI LITERATURE REVIEW REHABILITATION OF LOGGING GAPS AT PRA-ANUM FOREST RESERVE IN GHANAASIGBAASE MICHAELTable of Contents .......................................................................................................................................... ii i
    • List of Tables ................................................................................................................................................ iiiSections1.1 General Introduction ............................................................................................................................... 11.2 The problem of Deforestation ................................................................................................................. 21.3 Logging in Natural Forests ..................................................................................................................... 21.4 Impact of Logging on Forest and Forest Conditions .............................................................................. 31.5 Forest Rehabilitation ............................................................................................................................... 4 1.5.1 Enrichment Plantings ....................................................................................................................... 51.6 Choice of Tree Species for Rehabilitation .............................................................................................. 51.7 Native Tree Species ................................................................................................................................ 71.8 Growth Requirement of the Indigenous Species ..................................................................................... 7 1.8.1 Water ................................................................................................................................................ 8 1.8.2 Light ................................................................................................................................................. 8 1.8.3 Soil Characteristics .......................................................................................................................... 9 1.8.4 Spacing/Stand Stocking ................................................................................................................... 91.9 Conclusion .............................................................................................................................................. 9REFERENCES ........................................................................................................................................... 10List of Tables ii
    • 1. Table 1: Logging Impact on Forest 32. Table 2: Competition Potential of Species 63. Table 3: Perceived Potential Benefits of Native Species 6 1.0 Literature Review iii
    • 1.1 General IntroductionA forest is defined by the Secretariat of the Convention on Biological Diversity (2010) as acommunity or association of trees and animals dominated by trees which are capable ofgenerating forest products. These ecosystems produce valuable materials such as lumber,paper pulp, and domestic livestock that is important in human culture. They also play vitalroles in regulating climate, controlling water runoff, providing wildlife habitat, purifying theair and a host of other ecological services. In addition, these terrestrial biomasses havecultural, historic and scenic values and hence are usually protected (Lamb and Gilmour,2003; Secretariat of the Convention on Biological Diversity, 2010). However, forest is one ofthe most heavily disturbed resources by human activity. This work, therefore, is a review ofliterature on logging damage and the rehabilitation of forest after logging. It will focus on therehabilitation of logging gaps using native species.1.2 The Problem of DeforestationFor the past two decades, Central and West Africa recorded the highest deforestation rates;annual rate change of 0.6% from 1990-2000 and 0.5% for 2000-2005 (FAO, 2006). Ghanawas one West African country where deforestation was highest (Benhin and Barbier, 2001).Therefore, precise figures describing the current total forest cover and deforestation aredifficult to give (Hansen et al., 2009), though FAO, 2006 reported 24% of total land cover asGhana’s forest cover in 2005.The forests of Ghana are grouped into off-reserves and on-reserves. The ForestryCommission manages the on-reserve areas. There are 266 forest reserves in Ghana, out ofthis, 216 occur in the high forest zone which is the timber production zone (Damnyag et al.,2011). However, most of these reserves were already degraded in the mid 1990s as a result ofover-harvesting (over-logging) for timber, forest fires, and farming (Hawthorne and Abu-Juam, 1995). The situation, currently, may even be worse, because in 2006, the annualallowable cut had increased from 1 million m3 in 1989 to 2 million m3 (Blackett andGardette, 2008), without an equivalent replanting of trees (Damnyag et al., 2011). In Ghana,timber is extracted from the forest through selective logging (Palo and Yirdaw, 1996),involving periodic entries into a given area of a forest for the removal of selected commercialtimber trees using heavy extraction machines such as bull dozers, skidders and sometimestractors, which cause much damage to the residual forest. The method allows the removal of 2
    • only the current commercial trees while retaining those with potential commercial value forfuture use. This method of harvesting (selective logging) is one of the leading causes ofGhana’s forest loss through degradation and deforestation (Palo and Yirdaw, 1996).Therefore, the government of Ghana over the years have been concerned about the extent offorest degradation in the country (Damnyag et al., 2011). Rehabilitation measures, includingtree planting is one tactical effort being made to combat deforestation and to achievesustainable management (Damnyag et al., 2011). The 1994 Government policy thereforerecommends that degraded forest reserves should be put under reforestation and/orrehabilitation (Ministry of Lands and Forestry, 1994).1.3 Logging in Natural ForestsLogging is described by Stoddard and Stoddard (1987), as ‘the process of harvesting andhauling rough forest products from stump areas to the points of processing or sale’. Fellingand extraction of trees are the main activities during logging. The major aspect of loggingthat may contribute to degradation and eventually to deforestation is that besides damagedone due to felling some parts of the forests are cleared to construct tracks, roads, landingsand loading bays. Though logging affects the forest (Lamb and Gilmour, 2003), with propermanagement, it can be useful as matured trees have to be removed so that young trees cangrow to replace them. This however is not always the case, since it is dependent on propermanagement.Tree felling creates gaps in the forest canopy. This poses a serious threat to sustainability ifno silvicultural intervention appropriate for easing the recovery of logged areas is carried out(Asabere, 1987). The cumulative effect of these gaps together with skidding, roadconstruction, and loading bay operations can be very serious. The impact, however, varieswith logging intensity, frequency and spatial extent. The physical impact of loggingoperations, however, creates a structurally heterogeneous residual forest consisting ofdifferent micro-sites such as log landings, logging roads, logging gaps, loading bays and skidtrails (Stoddard and Stoddard, 1987; Demir et al., 2005).1.4 Impact of Logging on Forest and Forest ConditionsThe two main anthropogenic impacts on the tropical rain forests are deforestation and logging(Johns, 1997). Stoddard and Stoddard (1987) stated that harvesting timber from forested areashas both direct and indirect environmental effects. The level of impact as it relates to these 3
    • are, however, dependent on factors such as logging intensity, forest structure, terraincondition, harvesting methods and skill of machine operators (Johns, 1997 ; Stoddard andStoddard, 1987). Table 1 gives a summary of the impact of logging on forest and itsenvironment. Rehabilitation is therefore necessary to ease forest recovery after logging.Table 1: Logging Impact on ForestCONDITION CAUSE (S) CITATIONIncreased erosion Compaction, Top soil Kobayashi et al. (2001); removal for road and loading Batmanian (1990); Demir et bays construction, Reduced al. (2005); Sessions and rainfall interception Heinrich (1993)Nutrient loss Erosion, Top soil removal for Sophie et al. (2002); Demir, loading bay and road et al (2005); Buckley et al construction (2003)Reduced regeneration and Degradation and erosion Kobayashi et al. (2001);growth Sophie et al. (2002); Sessions and Heinrich (1993)Reduced infiltration and Compaction by machines Kobayashi et al. (2001);increased soil bulk density Batmanian (1990); Demir et al, (2005); Sessions and Heinrich (1993)Low porosity and moisture Loss of soil structure and ter Steege et al. (1996)retention characteristics surface litterResidual stand damage Felling operations, Absence Agyeman et al. (1999a); of pre- and/or post- harvest Hawthorne et al. (2001) treatmentHigher minimum and Increased solar radiation Wallace (1988); Burslemmaximum ground surface reaching forest floor due to (2004); Agyeman et al.temperature, Lower mean canopy openings (1999b)relative humidity, Greaterwind speedBiodiversity loss Habitat loss and competition Johns (1997); Gilliam for food (2002); Rab (2000)Forest Fires Logging residual served as Swaine et al. (1997) fuel bed1.5 Forest Rehabilitation 4
    • Gomez-Pompa and Burley (1991) observed that the natural regeneration process can be‘assisted’ or ‘directed’ to increase representation of any particular species. Forestrehabilitation is the human intervention to counter forest degradation processes e.g.,promotion of the recovery process in large gaps or conversion of shrub forest to high storeyplantation forest (Kobayashi et al., 2001). Forest rehabilitation therefore promotes measuresthat maximise forest functions especially after logging to satisfy human aims. It involves re-establishment of a more intact canopy that is found in undisturbed forest (Kobayashi et al.,2001). Replanting of commercial species has been a widespread means of supplementinginadequate natural regeneration and can be employed in rehabilitation projects after logging(Johns, 1997). For example, during the 1960s, areas of the West Mengo Forest Reserve,Uganda, which had been heavily damaged by logging and charcoal burning, were replantedwith selected timber species, including exotic hardwoods and it resulted in a considerableimprovement in timber increment (Johns, 1997). The seedlings are planted in natural forestgaps along regularly placed lines, or on heavily damaged open areas such as roads andloading areas (Johns, 1997). This implies that rehabilitation or enrichment planting may becostly and difficult to implement.1.5.1 Enrichment PlantingsEnrichment can conserve the soil and the forest environment, protect potential crop trees, andproduce additional wood or other forest products, leaf-fodder and fruits (Pancel, 1993). Someforests are damaged by heavy logging and harsh conditions such as low nutrient status, highirradiance, invasion of grasses and low soil moisture due to high evaporation are prevalent atthe gaps (Wallace, 1988; Burslem, 2004; Agyeman et al., 1999b). This poses problems toregeneration and the growth of young trees because germination and growth is dependent onsuch conditions as soil moisture content, invasive species, soil nutrient level and light(Gerhardt, 1993; Nepstad et al., 1990; Honu and Dang, 2000; Anning and Yeboah-Gyan,2007). Sometimes commercially attractive timbers may be lost because they were notrepresented in any advanced growth (i.e. saplings and trees smaller than the felling limit) orbecause the advanced growth was damaged by the logging operation hence enrichmentplanting has been suggested to assist natural regeneration (Weaver, 1987; Kopelainen et al.,1995; Sips, 1993).Enrichment planting is a way to enhance commercial productivity whiles maintaining thesites as essentially natural as in natural forests (Weaver, 1987; Aide et al., 2000; International 5
    • Tropical Timber Organization, 2002; Lamprecht, 1990). Planting fast growing andcommercially attractive species can speed up the forest recovery rate and enhance thecapacity of the forest to maintain commercial or social productivity by promoting the growthof economically desired species (Kobayashi et al., 2001). Enrichment planting also conservesany residual advanced growth or natural regeneration of timber trees and this in effect willmaintain much of the residual biodiversity that is still present in the forest (Kobayashi et al.,2001). However, since species suitability may vary with certain sites, the choice of nativespecies for rehabilitation should be carefully considered.1.6 Choice of Tree Species for RehabilitationThe decisive factors in choosing tree species for rehabilitation are usually both ecological andeconomic in nature (Pancel, 1993). Almost all the energy in the tropical forest ecosystemoriginates from solar radiation and trees differ in their tolerance to shade and light to suchdegrees that, ecologically, they are put them into two main classes: pioneer species and non-pioneer species (Swaine and Whitemore, 1988). The pioneer species are light demanders andfail to establish in deep forest shade. Examples are Fromager (Ceiba pentandra), Iroko(Milicia excelsa) and Framire (Terminalia ivorensis). These species are good forrehabilitation projects since they are able to grow in gaps (Longman and Jeniks, 1992).The non-pioneer species are further grouped into non pioneer light demanders and non-pioneer shade demanders. In moderate gaps, the non-pioneer light demanders such asEntandrophragma species, Khaya species, Bete (Mansonia altissima) and Ako (Antiaristoxicaria) perform appreciably better than the non-pioneer shade demanders (Longman andJeniks, 1992). This implies that these species may be extremely difficult to plant where gapsare large such as loading bays since they require some shading. Therefore, for effectivegrowth they should be established under some shade. The choice of species for rehabilitationprojects after logging should therefore be carefully considered and the appropriate speciesshould be used.Some species can better compete in logging gaps than others (Longman and Jeniks, 1992). Ifspecies whose competition potential is not known are considered for planting, it is advisableto observe their silvology in their natural environment (Pancel, 1993). The checklist in Table2 can be used to broadly evaluate a native species competitive potential is not known.Table 2: Competition Potential of Species; adapted from Pancel (1993) 6
    • Characteristics Competition BehaviourPioneer Species Rapid initial growth, competes successfully with weeds and climbersOpportunist Species Moderately tolerant to competitionLight Demanders Sensitive to competition from weeds and climbersShadow-tolerant May not be necessary or desirable to remove the indigenous forest growthOccurs in association with grasses Tolerates allelopathetic effects of grasses1.7 Native Tree SpeciesA native tree species is one that grows naturally in the country concerned, though notnecessarily in all parts and certainly not suited to all sites (Evans, 1992). In comparison to thetree species in the temperate regions, many tropical tree species possess natural propertieswhich make them practically useful. Such properties include natural durability, mechanicalstability and decorative appearance (Hall and Swaine, 1981). Therefore, cultivation ofindigenous timber species has both economic and ecological advantages over exotic specieswhich yield a high profit after a few years and are not slow growing as earlier thought (Foli etal., 1996). Table 3 presents the perceived potential benefits of native species.Table 3: Perceived Potential Benefits of Native SpeciesPerceived Potential Benefits CitationRestore biological diversity Lamb and Gilmour (2003)Sequester carbon Silver et al. (2000)Combat soil erosion Scott et al. (2005)Improve soil conditions Fisher (1995); Butterfield (1996)Enhance rural livelihoods Murray and Bannister (2004) 7
    • However, limited availability of information on native species has resulted in few of thembeing actually used in forest restoration programs. Understanding the growth characteristicsof forest trees will enhance their usage in rehabilitation programs.1.8 Growth Requirement of the Indigenous SpeciesThe growth of planted species is dependent on: environmental site conditions (soil, temperature, precipitation, distribution of precipitation and light) (Blatchford, 1978; Pancel, 1993); stocking of the stand (Pancel, 1993); silvicultural treatment (weeding, soil working, climber cutting, thinning) (Pancel, 1993 ), and, endogenous growth characteristics of the species (Johns, 1997; Assman, 1970; Blatchford, 1978).1.8.1 WaterThe supply of water is justifiably considered to be the key factor in tree growth and plays animportant role in determining the success of plantations, especially in the tropics (Longmanand Jeniks, 1992). Rainfall is the primary source of water and can be a limiting factor to treegrowth. For instance, according to Swaine et al. (1997), for adequate growth, M. altissimarequires a high rainfall of 2032 mm yr-1. Species like Cynometra anata and Tarrieta utiliscannot tolerate the dry season drought. The use of these species for rehabilitation should berestricted to the Evergreen Forest Zone where the seasonal drought is about four months(Swaine et al., 1997).In seasonally dry forest, growth is probably reduced owing to water shortage during the dryseason, unless the trees can tap water deep in the soil. At La Selva, Costa Rica, a detailedstudy of growth patterns on a day-to-day basis by Turner (2001) showed an annualperiodicity in growth in most of species on well-drained soils. Most species showed reducedgrowth in the mild dry season at La Selva. Similarly, during a severe drought in 1983 onBarro Colorado Island, there was considerably higher mortality among trees than normal,with large-diameter stems suffering the greatest increase in mortality (Turner, 2001). Thecase is not different in Ghana, the significant seasonal drought occurring each year in thedrier forest types, notably the Moist and Dry Semi-deciduous Forest types, have been foundto halt the growth of the trees. On the other hand, trees, which tolerate long drought periods, 8
    • example Terminalia mollis (ongo), Khaya senegalensis, and Afzelia africana can survive inthese areas (Swaine et al., 1997).1.8.2 LightThough tree species, ecologically, has been grouped into pioneer species and non-pioneerspecies, tree species growth is greatly influenced by light levels even within the same group.Turner (2001) observed that shading results in most forest trees growing at rates well belowtheir potential maximum. Also, studies in a deciduous dry forest in Mexico resulted inincreased growth when light was increased (Rincon and Huante, 1993). Therefore differencesin growth response to light conditions exist among species and affect the composition offorest stand (Hall and Swaine, 1981). Liebetman and Li (1992) found out that seedlingdensity was higher in well-shaded areas than exposed, open sites in a dry forest in Ghana.This may be due to the fact that light may be excessive in gaps in dry seasons thereforecreating higher desiccation hence increasing seedling mortality in large gaps. Therefore,species such as M. altissima will prefer moderate shade for the initial stages and subsequentlybecome a light demander requiring overhead light.1.8.3 Soil CharacteristicsAn interaction of several soil factors influence the growth of trees because changes in onefactor may bring about corresponding changes in the other factors. For instance, soilcompaction increases bulk density or strength of the soil, commonly called its mechanicalimpedances, and reduces its conductivity, permeability and diffusivity to water and air(Greenland, 1997). Soil characteristics such as texture, bulk density, compaction, moisture,penetration, thickness of the A horizon, organic matter and nutrient content can thereforepromote or retard the establishment and growth of forest trees (Kramer and Kozlowski,1979). However, Evans (1992) notes that luxuriance and richness of much tropical forestsdoes not primarily depend on fertile soil but on efficient recycling of nutrients in theecosystem.1.8.4 Spacing/Stand StockingStand stocking and spacing are inversely related (Kuuluvainen, 1991). Relatively widespacing of individual trees and their resultant crown development affect the rate of diametergrowth and the quality of the lumber or their products they yield (Nketia, 2002; Nkyi, 2007). 9
    • Crowding of trees in dense stands however has slightly stimulating effects on the heightgrowth which may exceed that of open grown trees.1.9 ConclusionThe current rapid deforestation rates, the dominance of non-commercial pioneers in logginggaps, lack of adequate regeneration for most commercial species, and current projections ofdramatic declines in the volume of future harvests calls for rehabilitation. Rehabilitation oflogged areas, loading bays, skid trails and road verges as well as landings is the most urgentmatter requiring enrichment plantings. With proper planning, site and species selection andmanagement, logging gaps can be rehabilitated after logging. This will ease forest functionrecovery through early canopy closer. 10
    • REFERENCES Agyeman, V.K., Abu-Juan, M. and Hawthorne, W. D. (1999a). Towards better forest harvesting, a summary of the findings of the research project: impact of harvesting on forest mortality and regeneration in the high forest zone of Ghana. Forestry Research Programme, Project R6716, Funded by the U.K., DFID, P.p 18. Agyeman, V.K., Swaine, M.D. and Thompson, J. (1999b). A comparison of gap microclimates in two forest types in Ghana. Ghana Journal of Forestry, 7, 51 - 69. Aide, T.M., Zimmerman, J.K., Pascarella, J.B., Rivera, L. and Marcano-Vega, H. (2000). Forest regeneration in a chronosequence of tropical abandoned pastures: Implications for restoration ecology. Restoration Ecology, 8, 328 - 338. Anning, A.K. and Yeboah-Gyan, K. (2007). Diversity and distribution of invasive weeds in Ashanti region, Ghana. African Journal of Ecology, 45, 355 - 366. Asabere, P. (1987). Attempts at sustainable yield management in the tropical high forests of Ghana. In: F Mergen and J R Vincent (eds.) Natural management of tropical moist forests: silviculture and management prospects of sustainable utilization, Yale University press, New Haven, CT, pp. 47 - 49. Assman E. (1970). The principles of forest yield study. Pergamon Press, Oxford. Batmanian, G.J. (1990). Reforestation of degraded pastures in Brazilian Amazon: effect of site preparation on phosphorous availability in the soil. PhD thesis, University of Georgia, Athens, GA. Benhin, J.K.A. and Barbier, E.B. (2001). The effects of adjustment in Ghana of the structural program on deforestation. Agricultural and Resource Economics Review, 30, 66 - 80. Blackett, H. and Gardette, E. (2008). Cross-border flows of timber and wood products in West Africa. Final Report, HTSPE Ltd, European Commission, Contract Reference: 2007/146818. Blatchford, O.N. (ed.) (1978). A summary of methods of establishing, maintaining and harvesting forest crops with advice on planning and other management considerations for owners, agents and foresters. Forestry Commission Bulletin No. 14, pp. 1. Buckley, D.S., Crow, T.R., Nauertz, E.A. and Schulz, K.E. (2003). Influence of skid trails and haul roads on understory plant richness and composition in managed forest landscapes in Upper Michigan, USA. Forest Ecology and Management, 175, 509 - 520. 11
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