Mixed species forest plantations can provide both economic and ecological benefits over monoculture plantations. Mixing tree species that utilize resources in complementary ways through differences in canopy structure, rooting depths, or phenology can increase overall stand productivity. Facilitative interactions between species that improve environmental conditions or resource availability can also boost yields. However, mixed plantations require matching species combinations to site conditions and managing complex inter-species interactions to realize potential benefits over simpler monoculture systems. More research is still needed to better understand mixed plantation dynamics and help optimize species selections and layouts for different goals and locations.

1. MODULE 2.2. FOREST PLANTATION MANAGEMENT SYSTEMS
Srinivasan korappath

2. Forest plantations : 5% of global forest cover (187 mha) &
35% round wood/timber
(FAO,2001)
Mixed species plantations
Individual plantations containing more than
one timber species. The plantation contain
few or many tree species planted in rows or
at random (Fig.1d-1g)

3. To maintain an equilibrium between economic
and ecological function of the plantations….
Ecological restoration of degraded lands to re
establish part of the native diversity
Goal is to combine particular species so as to
provide specific interaction that increase stand
level productivity.

4. Mixed plantation lay outs to biodiversity(Lamb,1998)
d) Mixed species plantation established using 2 Spp. Planted in
alternative rows
e) Planted at random
f) Four species planted in rows
g) Four species in random

5. To improve the productivity in mixed plantations, there are
three main processes that need to be considered: competition,
competitive reduction and facilitation (Vandermeer, 1989 and
Kelty, 1992).
Competition: negative effect
Competitive reduction, also known as complementarity or the
competitive production principle (leading to a more complete use of
site resources)
Facilitation, also known as the facilitative production principle

6. The way in which competition is distributed in a
stand of trees depends on the resources for
which plants are competing (Weiner,
1985,1986 and 1990)
Competition for light
Competition for belowground resources, such as water and
nutrients
variations in fine-root architecture, growth rates, distribution
and mycorrhizal associations may also lead to asymmetrical
competition belowground.

7. The occurrence of both interspecific and
intraspecific competition leads to more
complex interactions in mixtures than
monocultures.

8. The yield of mixtures containing species A and B, where the proportion of each species
in mixture changes from no individuals (0) up to x individuals and the total number of
individuals remains constant (adapted from Harper, 1977). Depending on the nature of
the interaction between species, there may be substitution (a and b), a reduction in yield
(c), or an increase in yields (d–e).

9. occur spatially through the stratification of foliage or roots or
temporally due to phenological differences
stratification—
*Canopy stratification—competition for light (stratified canopies with a
fast-growing and less shade-tolerant species forming the upper canopy and
a more shade-tolerant species forming the lower canopy :light use efficiency
of the stand is more)
stratification—
*Root stratification—competition for nutrients and water
The potential reduction of below ground competition occurs through the
physical (differences in fine-root distribution that affect exploitation
strategies) or chemical stratification (co-occurring species employ different
acquisition strategies to obtain nutrients) of roots.

10. more diverse plantations should have higher
net primary production,
and in a well-managed plantation, this should
translate into larger timber volumes

11. directly, by the amelioration of harsh environmental
conditions or through increased resource availability,
indirectly, via the elimination of potential competitors, the
introduction of beneficial organisms (mycorrhizae and
other soil microbes) or protection from herbivores
(Callaway, 1995).
Facilitation often occurs simultaneously with competition,
and the complex interactions between these mechanisms
determine the overall productivity (Callaway, 1995 and
Holmgren et al., 1997)

12. Schematic diagrams of four mixed-species
plantation designs, each with
two species. Each diagram shows the
plantation at the sapling stage and mature
stage: (source:Kelty,2006)
(A)fine-grained mixture with stratified canopy
with equal proportions of species, for
complementary resource use (facilitative
interaction may also be present);
(B) fine-grained mixture similar to (A) but with
unequal proportions of species, to promote
individual-tree growth of upper canopy
species and reduce suppression of lower
canopy;

13. (C) coarse-grained mixture for facilitative
interaction, to limit the overtopping of timber
species by fast-growing N-fixing species;
(D) fine-grained mixture with delayed planting
of fast-growing N fixing species, for same
objective as in (C)

14. successful mixed-species plantations require
the matching of the species combination with
the site so that the competitive interactions
are minimised while the competitive reduction
and facilitative interactions are maximised.

15. Relative yields of Eucalyptus globulus and Acacia mearnsii growing in 1:1 mixtures at age 50 weeks in
a pot trial, RY > 0.5 indicates that plants were larger in mixture than in monoculture. Modified from
Forrester et al., 2006a and Forrester et al., 2006b.
indicated that a very fast growing and
efficient user of site resources, such as many
Eucalyptus spp., planted on a site with high
resource availability may not produce higher
yields when grown in mixture.

16. Mixed plantings obviously increase the biodiversity.
There is a production gain from using a nitrogen fixing
species such as Acacia or Albizia species as the tree
species in nitrogen deficient sites.
There is production gain from the reduced inter specific
competition as a result of mixing trees with contrasting
phenologies (seasonal variation) or with different root or
canopy architecture(occupation of growing space):
complementary resource use/good ecological combining
ability
Mixed plantation can be less susceptible to serious fungal,
insect, or animal damage than plantation monocultures

17. Financial or social benefit may be derived from
harvesting early maturing species ( a mixture of
commercially useful, early maturing species with a
slow growing (high value species :needing more
rotation time) is preferred)
Mixing agriculturally or socially important plant
might provide a greater range of harvestable
products(e.g., fruits and nuts)

18. A mixture of shallow rooted species with deep
rooted species will have less wind damage.
More successful on poor sites than monocultures.
Mistakes made in the selection of species for
artificial regeneration can be easily corrected in
mixed stands when compared to monoculture.
A mixed stand is more easily transformed or
modified to meet the present or probable future
demands of the market (reduce risk of market
shift).

19. In some cases net benefits of the mixture may take
some time to appear.
They are more difficult to manage : (grow at different
rates and require different harvesting times)
There is a possibility that slow growing species may be
damaged when the earlier maturing species is removed
(lay out such as 1d and 1f may overcome this by row
thinning.
Potential benefits have not always been realized in
practical situations

20. Choices of species used in the mixture have a crucial
role in deciding the success of a mixed plantations.
(Which will form complementary/competitive etc?)
More knowledge is required about the attributes of the
potential plantation species(growth rate, phenologies,
architectural features):
More needs to be known about the circumstances in
which mixtures actually increase yields, or reduce
disease, herbivory or other insect damage over that
occur in monocultures).

21. One of the main obstacle to the commercial uptake of poly
cultures in industrial plantations may be lack of
operational scale demonstrations coupled with reliable
financial analysis.
In a financial analysis of mixed species plantations
(Nicholas et.al., 2006), it was observed that a yield
stimulus of 10% (based on the product and rotation) was
needed to offset increased costs associated with planting
and management of of mixed species plantations.
Allelopathic effect, some times host for potential predators

22. Management is simplified (silviculture,
harvesting, uniform products)
The crop can be harvested economically
Artificial restocking is simpler
The ability to concentrate all site resources on
the growth of a species with good vigour and
wood quality.

23. (Lamb,1998)

24. Can polyculture provide greater yield to
outweigh the management simplicity of
monocultures??

25. By mixing species of both ecological and economic
combining ability mixed plantation can certainly
outweigh the monetary benefit from monoculture
but climate change and escalating energy prices
may impact on the efficiency of monoculture
plantations and stimulate further interest in
polycultures.
More innovative experiments ( replicated spatially,
temporally and with alternative species) is needed.

26. Dr.H.Pohris
Mr. Andrew

27. Danke