Competition, predation, mutualism and
commensalism in Agroforestry systems
By-
Vikas Belwal
Id. 23421
Ph.D. Tree Improvement
Agroforestry Research and Management
AGF 601
Agroforestry systems
• Is characterized by the integration of trees or shrubs with crops or
livestock, providing multifaceted ecological niches where a number of
interactions occur.
• Agroforestry systems, are intricate ecosystems (where trees, shrubs, and
crops coexist), presenting opportunities for competition, predation,
mutualism, and commensalism.
• Agroforestry, offers a unique setting for studying these ecological
interactions. Understanding and managing these ecological interactions are
essential to sustainable agriculture.
The interaction of species is
mediated by the environment
through the ‘response and
effect’ principle (Goldberg &
Werner 1983) which states that
plants and the environment
modify each other so that the
environment causes a response
in plant function and growth
while the plant affects the
environment by changing one
or more of its factor (Clements
1928).
Competition
• Competition arises when species compete for limited resources, including food,
water, territory, and mates.
• Agroforestry systems, which integrate multiple plant species, offer a unique
environment where competition for resources like sunlight, water, and nutrients
becomes a critical factor.
• Understanding the mechanisms and consequences of competition is essential for
optimizing land use and ensuring sustainable agriculture.
• Intraspecific competition, within a species, and interspecific competition,
between different species, drive natural selection and evolution.
• Managing species composition and spatial arrangement is crucial to mitigate
detrimental competition.
Mechanisms of Competition
• Resource Competition: Trees, shrubs, and crops compete for essential
resources like sunlight, water, and nutrients. Shade-tolerant crops may
thrive under tree canopies, but light-demanding crops can suffer from
reduced photosynthesis and yield.
• Root Competition: Below-ground competition for soil space and nutrients
is prevalent. Deep-rooted trees may outcompete crops for water and
nutrients, impacting crop growth. Higher rooting densities promote
competition for nutrients due to decreasing inter-root distances (Gillespie
1989).
• Allelopathy: Some tree species release allelopathic chemicals that inhibit
the growth of neighboring crops. Understanding allelopathic interactions is
crucial for selecting compatible plant combinations.
Implications
• Yield Reduction: Unmanaged competition can lead to reduced crop
yields, undermining the economic viability of agroforestry systems.
• Spatial Arrangement: The spatial arrangement of plant species within
agroforestry systems influences competition. Proper design can
mitigate negative effects and enhance overall productivity.
• Crop Selection: The choice of crop species should consider their
compatibility with the tree or shrub species present, optimizing
resource utilization.
Strategies for Managing Competition
• Companion Planting: Selecting companion plant species that complement
each other in terms of resource use can reduce competition. For example,
nitrogen-fixing trees can enhance soil fertility, benefiting associated crops.
• Pruning and Thinning: Regular pruning and thinning of trees and shrubs can
reduce competition for light and resources, benefiting both tree growth and
crop productivity.
• Species Selection: Careful selection of tree, shrub, and crop species based
on their growth habits and resource requirements can minimize
competition.
• Spatial Arrangement: Strategic planting patterns, such as alley cropping and
silvopasture, can optimize resource distribution and reduce competition.
Examples
Agroforestry Alley Cropping:
• In alley cropping systems, rows of trees are planted alongside rows of
crops.
• The competition for sunlight and space between tree rows encourages
crops to grow taller and more erect, reducing competition for light.
• This competition relationship can lead to increased crop yields and
improved tree growth.
Resource Partitioning Among Crops:
• Different crop species with varying resource requirements can be
interplanted in agroforestry systems. Resource partitioning reduces
competition for nutrients, water, and light among crops.
• For example, deep-rooted crops like maize can be grown alongside
shallow-rooted crops like lettuce.
Vertical Stratification of Plants:
• Agroforestry systems can create vertical stratification where trees
occupy the upper canopy layer, shrubs the mid-layer, and crops the
lower layer.
• This stratification minimizes competition for sunlight and allows for
efficient use of vertical space.
Resource-Conserving Crops and Trees:
• Resource-conserving crops like drought-resistant varieties can be
integrated with trees.
• These crops are adapted to resource-limiting conditions and may
thrive despite competition for water and nutrients.
Competition for Water Resources:
• In arid or semi-arid regions, agroforestry systems can feature trees
that compete with weeds for water resources.
• The presence of trees can reduce weed growth and competition for
water, benefiting crops.
Predation
• Predation encompasses the predator-prey dynamic, where one species
hunts and consumes another.
• Predation, a key ecological process, plays a multifaceted role in
agroforestry systems and encompasses both beneficial and detrimental
aspects.
• While certain trees provide habitats for beneficial predators that control
pests, others may attract herbivores harmful to crops.
• Understanding how predation affects these systems is vital for pest
management and enhancing ecosystem services.
Beneficial Aspects of Predation
• Natural Pest Control: Predators such as birds, insects, and spiders can
contribute to biological pest control within agroforestry systems. They
prey on herbivorous pests, reducing crop damage and the need for
synthetic pesticides.
• Biodiversity Enhancement: The presence of diverse plant species in
agroforestry systems can attract a wide range of predators, promoting
biodiversity and ecological resilience.
Detrimental Aspects of Predation
• Herbivore Predation: Some trees or shrubs may attract herbivores
that damage crops. Effective management is required to balance the
positive and negative aspects of predation.
Strategies for Optimizing Predation
• Habitat Diversity: Maintaining diverse vegetation within agroforestry
systems provides shelter and food sources for predators. Strategic planting
can attract and support beneficial predator populations.
• Native Species: Prioritizing the use of native plant species can enhance the
presence of native predators, which are often better adapted to the local
ecosystem.
• Integrated Pest Management (IPM): IPM strategies should incorporate
predation as a component of pest control, considering the role of beneficial
predators in reducing pest populations.
• Predation in agroforestry systems is a dynamic process influenced by
the composition and structure of the ecosystem.
• It holds great potential for enhancing pest control and biodiversity. By
fostering a habitat that supports beneficial predators and integrating
predation into pest management strategies, agroforestry can
contribute to sustainable and resilient agricultural systems.
Examples
Bird Predators and Insect Pests:
• Birds, such as swallows, sparrows, and finches, are natural predators of
many insect pests like aphids, caterpillars, and grasshoppers,
contributing to effective biological pest control.
• In agroforestry systems, the presence of diverse vegetation and trees can
attract these birds.
• Beneficial Insects and Pest Control:
• Ladybugs, lacewings, and parasitoid wasps are examples of beneficial
insects that prey on crop-damaging pests.
• Agroforestry systems with diverse plant species provide habitat and
nectar sources for these predators.
Amphibians and Insect Control:
• Amphibians, such as frogs and toads, are natural insect predators.
• Agroforestry systems with water bodies or wetland components can
support amphibian populations. In turn, they may help control insect
pests in and around agroforestry fields.
Beneficial Nematodes and Pest Control:
• Some beneficial nematode species are predators of soil-dwelling
insect larvae.
• In agroforestry systems, these nematodes can naturally regulate pest
populations, reducing root damage to crops.
Mutualism
• Mutualism is a symbiotic interaction where both participating species
benefit.
• Agroforestry systems, provide a fertile ground for mutualistic
relationships. It is a key driver of improved soil fertility, enhanced crop
resilience, and reduced environmental impact.
• Mutualistic relationships in agroforestry systems are exemplified by
nitrogen-fixing trees, which enhance soil fertility and reduce the need for
synthetic fertilizers.
• These interactions are dynamic and influenced by species composition,
environmental conditions, and management practices.
Nitrogen-Fixing Trees
• Symbiotic Nitrogen Fixation: Nitrogen-fixing trees, such as legumes,
form symbiotic relationships with nitrogen-fixing bacteria (e.g.,
rhizobia). These trees host nodules on their roots, where bacteria
convert atmospheric nitrogen into a form usable by plants.
• Enhanced Soil Fertility: The nitrogen fixed by these trees enriches the
soil with a vital nutrient, reducing the need for synthetic fertilizers
and improving overall soil fertility.
Other Mutualistic Interactions
• Mycorrhizal Symbiosis: Mycorrhizal fungi form mutualistic associations
with the roots of many plants, including trees and crops. These fungi
enhance nutrient and water uptake for host plants, improving their growth
and resilience.
• Pollinators: Trees and shrubs in agroforestry systems can attract pollinators
such as bees, benefiting crop pollination and yield.
• Companion Planting: Selecting companion plants with mutually beneficial
characteristics, like pest-repelling properties or complementary resource
requirements, can enhance crop health and productivity.
Management Strategies
• Species Selection: Choosing nitrogen-fixing tree species and
mycorrhizal-friendly crops is essential to optimize mutualistic
benefits.
• Sustainable Practices: Employing sustainable practices that support
beneficial interactions, such as reducing chemical inputs and
preserving pollinator habitat, enhances mutualistic relationships.
Mutualistic interactions within agroforestry systems, particularly
involving nitrogen-fixing trees and mycorrhizal fungi, offer sustainable
solutions to soil fertility and crop production challenges. Harnessing
and preserving these relationships are crucial for achieving resilient and
productive agroecosystems.
Examples
Nitrogen-Fixing Trees and Crops:
• Leguminous trees, like acacias or mesquites, often form mutualistic
relationships with nitrogen-fixing bacteria (rhizobia) in their root nodules.
• These trees fix atmospheric nitrogen into a form that crops can utilize, thus
enhancing soil fertility. Common companion crops like maize, beans, or
soybeans, may get benefited.
Mycorrhizal Fungi and Plants:
• Mycorrhizal fungi form mutualistic associations with the roots of many tree
species in agroforestry systems.
• These fungi extend the root system's reach, increasing nutrient and water
absorption. Trees such as pines or oaks may enhance the growth of
associated crops like coffee, cocoa, or fruit trees.
Bees and Fruit Trees:
• Bees are essential pollinators in many agroforestry systems that include
fruit-bearing trees.
• The mutualism between bees and fruit trees results in improved fruit set,
leading to higher crop yields. Apple orchards, citrus groves, and mixed fruit
tree systems often rely on this relationship.
Cattle and Grass-Legume Pasture:
• In silvopastoral systems, where trees are integrated into livestock grazing
areas, grass-legume pastures can be established.
• Legumes like clover or leucaena fix nitrogen, enhancing soil fertility and
providing a protein source for grazing animals.
• This mutualistic relationship benefits both soil health and livestock
nutrition.
Commensalism
• Commensalism represents an intriguing form of species interaction where
one species benefits without harming the other.
• Commensalism, a subtle yet vital ecological interaction, frequently occurs
within agroforestry systems.
• Commensalism often manifests through tree shade, microclimate
modification and residue decomposition.
Beneficial aspects
• Shade Provision: Trees in agroforestry systems offer shade to
understory crops during hot and sunny periods, mitigating heat stress
and reducing water loss through transpiration.
• Microclimate Modification: The presence of trees can alter local
microclimates by decreasing temperature extremes and wind velocity,
creating more favorable conditions for crops.
• Nutrient Recycling: Fallen leaves, branches, and crop residues that
accumulate beneath trees create a nutrient-rich environment. Soil organisms
break down these materials, releasing nutrients that benefit both crops and
trees.
• Improved Soil Structure: Decomposing organic matter improves soil
structure, water-holding capacity, and aeration, enhancing overall soil health
and productivity.
• Reduced Irrigation: The shade provided by trees can reduce water
requirements for crops, contributing to water conservation.
• Improved Biodiversity: The altered microclimates and nutrient-rich
environments can attract diverse flora and fauna, further enhancing
ecosystem stability.
Management Strategies
• Strategic Planting: Deliberate placement of taller trees to provide shade to
specific crops can optimize commensal benefits.
• Mulching: Applying tree leaves and crop residues as mulch around crops
can further enhance soil quality and water retention.
• Commensalism in agroforestry systems, characterized by shade
provision, microclimate modification, and residue decomposition,
offers a wealth of benefits that are often underestimated.
• These interactions, often unintentional, have far-reaching
consequences on crop yield, resource use efficiency, and biodiversity.
• Recognizing and harnessing these unintended interactions can
contribute to more sustainable and resilient agricultural practices.
Examples
Tree Shade and Crop Health:
• In agroforestry systems, taller trees can provide shade for understory crops.
• While trees benefit from the presence of crops by providing additional
habitat, crops primarily gain from reduced heat and evaporation.
Microclimate Modification:
• Trees can modify local microclimates. They reduce temperature extremes and
wind velocity, creating more favorable conditions for crops.
• Trees benefit from the presence of crops as they do not rely on microclimate
modifications.
Crop Residue Decomposition Under Trees:
• Fallen leaves, branches, and crop residues accumulate beneath trees in
agroforestry systems.
• Soil organisms break down these materials, releasing nutrients into the soil.
This nutrient enrichment benefits both the trees and the associated crops.
Microbial Activity Under Trees:
• Microbial communities under trees may be more active due to the
presence of decaying organic matter.
• This enhanced microbial activity can improve soil health and nutrient
availability for both trees and crops.
Conclusion
• The ecological principles of species interactions—Mutualism, Competition,
Predation and Commensalism form the foundation of future research.
• The dynamic interplay of these interactions shapes the sustainability and
productivity of agroforestry systems.
• Acknowledging the delicate balance of these interactions is crucial for effective
conservation, habitat management, and sustainable production systems.
• Further research in this field is required to uncover new insights into these
interactions, offering invaluable tools for the stewardship of agroforestry system.
References
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connecting each and every organism.
• Lloyd S. Anderson and Fergus L. Sinclair. Ecological interactions in
agroforestry systems. Bangor Research Unit, Institute of Terrestrial Ecology.
• Agroforestry Abstracts (1993) 6 (2) 57-91.
• Daizy Rani Batish et.al. Ecological basis of agroforestry. CRC Press.
• S. Jose, A.R. Gillespie and S.G. Pallardy. Interspecific interactions in
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Thanks
