Biodiversity and functioning: agro-ecosystems

Question 1

modern agriculture vs natural systems

Answer 1

Modern agriculture
- v intensive (high input) monocultures
- Often control composition, density, spatial arrangement, phenology (planting time)
- Focus on production (not multifunctioning) = high yielding BUT low diversity
- Inputs: fertiliser, pesticide, herbicide, water, pollinators

Natural system
- Species coexisting
- More productive and stable due to niche differentiation leading to niche complementarity
- > Complementary resource partitiong (type, time and space)
- > Nurse crop (shelter while grow)
- > Reduction of natural enemies (pests, weeds, disease)
- > Increase pollinator abundance/ richness

Question 2

Intercropping

Answer 2

cultivated multiple species on same land

Types:
- Spacial: fully mixed or rows

• Temporal (within a year):
• > relay (lifecycle of one crop overlaps w/ different part of lifecycle of another crop )
• -> Example: The soybeans grow beneath the canopy of the wheat until the wheat is harvested, at which point the soybeans continue to grow and are harvested later in the season
• > temporal (crops planted one after another)

It is favoured if:
- Costly / impossible to use inputs to reduce environmental variability
- no single species monoculture will exhibit high yield under wide range of conditions
- Diversity through niche differentiation may enhance yield under these spatially heterogeneous and temporally fluctuating conditions.
- The aims are to sustainably intensify production while reducing conventional inputs
- To optimize both yields and ecosystem services.

Question 3

Measuring overyeild due to intercropping

Answer 3

land equivalent ratios (LER)

LER = ratio of yeild under monoculture vs yeild under intercropping of each plant added together (>1 = overyeilding)

Question 4

Intercropping examples

Answer 4

Corn-bean-squash companion planting
- Corn = 3D vertical support for beans
- Beans = N fixation + antiherbivore (due to hairs on beans)
- Squash = ground layer suppressing weds, reducing evaporation
- fourth sister = Cleome surrilata (rocky-mountain bee plant) to attract bee pollinators for bean / squash

Coffee:
- Sun-tolerant coffee varieties developed so can grow as monoculture
- Initially grown with trees (agro forestry)
- Biodiversity benefits to birds: 61 bird species in sun grown vs 243 bird species in shade grown
- If many other species than may decrease yield, but offset by higher priced product as more bird friendly

Pull push plants
- Plant to attract pest, plant to repel pest and main crop
- Example: Alternate rows of Maize and Desmodium uncinatum (repellant), with three rows of Napier grass Pennisetum purpureum planted around plots (attractant)

Question 5

Evidence of benefits

Answer 5

Cedar Creek and Jena experiments
- show polyculture has increased ecosystem function (forage yield, soil organic matter, yield stability, pest / weed suppression, soil fertility) compared to monoculture

Hann and Cammarano (2022)
- intercropping Suppresses natural enemy impacts on 68% of species
-> Compound release
-> Reduced tranmission
-> Reduced specialisation

• Suppressed weeds in 86% of species
• > phsyical barrier
• > Sun shade
• > Compound release

Li et Al, 2023
- improvement in plant nutrition -> protein better calorie worse

Question 6

Example: Rice and tropical rain forest

Answer 6

Rice blast = fungal pathogen

intercropped species:
- Glutinous stick rice = higher value + lower yields
- Non-glutinous hybrid varieties = less susceptible to rice blast but less valuable crop

Results
- mixture yield increased by 89% compared to monoculture
- blast 94% less severe than in monoculture (as height difference between tall glutinous and short hybrid affect temp, humidity and light and make worse for blast)

Intercropping socioeconomically feasible as both crops are utilised
-> Glutinous = exported
-> Non-glutinous = eaten locally

Question 7

Example: Borneo forests

Answer 7

Restoring deforestation and abandoned oil plantation

• Restored to better vegetation cover if planted w/ polyculture mixtures
• although replanting w/ monocultures is best at first, but then benefit slows

Question 8

Barriers & challenges erview

Answer 8

• Traditional intercrops were harvested by hand whereas intensive monocultures are often harvested by machine -> must Develope mixture-friendly machinery and systems
• Other infrastructure is often optimized for a standardized single crop, e.g. sawmills for spruce of a certain size range
• Requires Markets for the intercrop components (rice example)
• ‘Monoculture thinking’ as the basis of modern agriculture
• Vested interests in supplying the inputs to intensive monocultures (fertilizer, herbicides, pesticides)
• Identify complementary mixtures and how to best grow them (density, timing etc.)
• Maintaining optimal conditions

Question 9

Overview

Answer 9

Increasing diversity can increase crop and forage yield, yield stability, pollinators, and weed, pest and disease suppression.

When to use intercropping?
- The aims are to sustainably intensify production while reducing conventional inputs
- To optimize both yields and ecosystem services.
- High inputs required to reduce condition variability

Examples:
- Coffee
- The three sisters
- Push and pull

Success stories:
- Rice

Limitations

Over the next decades, if monoculture yields continue to decelerate or decline and as demand for ecosystem services continues to rise, diversification could become an essential tool for sustaining production and ecosystem services in croplands, range-lands and production forests