FINAL4 Trees in agroecosystems Flashcards
Microclimate effects
lower soil temperature alter soil moisture minimize temperature fluctuations Shade effects Reduce wind Resistance/resilience effects – moderate extremes?
4 ecological principles to aid in design:
- spatial and temporal heterogeneity
- importance of disturbance in ecosystem structure and function
- perennialism is the most common condition in natural vegetation
- structural and functional diversity important but hard to quantify
(Emphasize need to understand and manipulate tree/crop interactions in design of agroforestry systems)
Maintain or increase soil fertility
biological nitrogen fixation (if leguminous or associated with Frankia symbiosis)
reduce nutrient loss
nutrient pumping from sub-soil (how significant?)
litterfall, root turnover, and root exudate
Resistance/resilience effects – retain nutrients?
Maintain or increase soil organic matter
from leaf litter, root turnover, and root exudates, lack of disturbance
improved soil physical qualities and nutrient availability
increases microbial activity - suppressive soils?
Resistance/resilience effects – improve soil stability
Reduce soil erosion
via cover of canopy and mulch on soil surface
as barrier on slopes to catch and slow down runoff
roots hold soil in place
Resistance/resilience effects – retain good topsoil
Harvest potential
increased diversity of products
tree crop products (fruit, nuts, leaves),fodder, wood products, medicinal products, plus whatever is produced between the trees
Resistance/resilience effects
diversity of income/food sources
What is Agroforestry?
the intentional combining of agriculture and working trees to create sustainable farming and ranching systems.
What is a windbreak?
Plantings of single or multiple rows of vegetation (trees, shrubs, grass) that are established for one or more environmental and economic purposes
What are the benefits to windbreaking?
Reduce soil erosion Protect plants Enhance plant growth Manage snow Provide shelter Reduce energy needs Improve wildlife habitat Enhance aesthetics Moderate noise Screen views Reduce airborne chemical drift Improve irrigation efficiency Increase carbon storage Mitigate odors
What are the effects of windbreaking?.
Windbreaks:
lower wind velocity causing air-borne material to be deposited
physically trap air-borne material
adsorb some of the chemicals attached to air-borne material
alter the microclimate on the downwind side of the windbreak
Why is density important for windbreaks?
Dense: maximum wind reduction but short wind shadow
Moderately dense: less wind reduction but longer wind shadow
Why is orientation important for windbreakers?
Location or layout:
Directly influences area protected
Effects vary with critical weather periods and wind directions
Why is length important for windbreakers?
For full protection, the windbreak needs to extend the entire length of the area needing protection to account for changing wind directions.
Doubling the length of a windbreak will generally increase the area protected by 4 times
Why is height important for wind breakers?.
H = Effective height of the windbreak
The height determines the distance of the downwind sheltered (protection) zone
Why is width important of windbreakers?
Width influences:
Density
Wildlife values
Trapping capacity and efficiency
Why is continuity important for winbreakers?
Wind speed increases in a gap
Gaps in the windbreak can result in damage or complications downwind
Types of windbreaks:
-field
-livestock
-
Multi-purpose windbreaks
Bio-energy feedstock
Food security
Wildlife
Income products
What is silvopasture
Combining timber, livestock and forage production on the same acreage. Trees provide long-term returns, while livestock and forages generate an annual income.
Management System Components
trees-forages-livestock
Silvopasture Benefits
Improved plant vigor Lower animal stress Reduced wildfire risk Improved wildlife habitat Annual income Long-term income
Silvopasture Benefits-lower animal stress
Increased weight gain
Increase milk yields
Higher conception rates
Lower veterinarian bills
Silvopasture Benefits-reduced wildfire risks
Reduced: Stand density Ladder fuels Fuel loading Winds
Silvopasture Benefits-Improved wildlife habitat
Sufficient food supplies
Suitable cover
Well distributed water
Adequate habitat
Riparian Forest Buffer
What: An area of predominantly trees and/or shrubs located adjacent to and up-gradient from watercourses or water bodies
Where: On areas adjacent to permanent or intermittent streams, lakes, ponds, wetlands and areas with ground water recharge that are capable of supporting woody vegetation.
Use Riparian Forest Buffers to:
Create shade to lower water temperatures & improve habitat for cold water aquatic organisms
Provide a detritus and large woody debris for aquatic and terrestrial organisms
Create wildlife habitat and establish wildlife corridors
Restore natural riparian plant communities
Reduce excess amounts of sediment, organic material, nutrients and pesticides in surface runoff and in shallow ground water flow
Provide a harvestable crop of timber, fiber, forage, fruit etc.
Protect floodplain integrity
Increase carbon storage
Riparian Forest Buffer Design Considerations
Three-zone buffer system
Buffer widths and zones influence use and functionality
Minimum zone widths will vary by region
Riparian Forest Buffer Reduce excess contaminants
Understand the source contaminants and locate the buffer down-gradient from them.
Contaminants (sediment, chemicals, etc.) may be transported by surface sheet runoff or concentrated flows or by subsurface flows.
Subsurface flows in many settings bypass riparian buffer root systems
Riparian Forest Buffer Provide floodplain protection
Riparian buffers reduce floodwater velocity and erosive power
Stream debris is blocked from entering cropland, grassland, and urban lands
Roots hold stream banks and keep the soil in place
Peak storm flows may be reduced, lowering flooding levels
Riparian Forest Buffer Provide detritus and woody debris
Detritus and large debris are particularly important for stream/riparian food chains
Placement in close proximity to the stream or water body insures that some leaf drop, twigs, and other detritus (and eventually large woody debris) enters the aquatic system.
Riparian Forest Buffer Create wildlife habitat
Use widths to match desired conditions
Value of riparian habitat increased if adjacent upland habitat is created
Natural tree mortality can increase habitat diversity
Full site functionality takes time
Restore natural plant communities
Wildlife benefit from a mosaic of natural plant communities
Connect fragmented riparian forests.
Isolated patches may be under-utilized or act as a magnet for predators
Use native species where ever possible
Riparian Forest Buffer Provide harvestable crops
Marketable products depend on current and future demand.
Potential products:
wood (sawlogs, post, poles, veneer)
fiber (pulp, firewood, energy biomass)
forage (livestock)
fruit (nuts, berries)
other crops (ginseng, mushrooms, herbs and floral greenery, etc.)
Riparian Forest Buffer Increase carbon storage
Riparian buffers are effective at storing carbon
Trees grow rapidly in riparian zones due to favorable moisture and nutrient conditions
Net carbon benefits are realized if the wood fiber is used for solid wood products or fuel
What is Alley Cropping
the planting of trees or shrubs in two or more sets of single or multiple rows with agronomic, horticultural, or forage crops cultivated in the alleys between the rows of woody plants.
Alley Cropping Benefits
Improves crop or forage quality and quantity by enhancing microclimate;
Improves the microenvironment to increase crop yieldsProtects alleyway crops from physical damage from winds
Alley Cropping Benefits
Improve Crop Diversity, and Economic Returns
Allows production of annual crops for cash flow while growing longer term woody investments.
Allows two crops to be grown on the same acreage such as a forage or row crop and nut or fruit crops
Allows crop diversity which reduces risk
Alley Cropping Benefits
Increases net carbon storage in the soil and vegetation
Roots, crop residue, leaves and forage add to soil carbonTrees add to total carbon stored on site through sequestration in the above ground and below ground biomass
Alley Cropping Benefits
Improves utilization and recycling of soil nutrients
Tree roots are generally deeper than crop roots
Nutrients and chemicals that pass through crop root zone are intercepted by trees
Nutrients are utilized by the trees and recycled back to the soil surface by leaf drop
Alley Crop Benefits
Decreases off site movement of nutrients or chemicals - surface
Trees planted on contour trap sediment and residue along with attached nutrients and chemicals
Infiltration increases in tree rows decreasing overland flow and associated movement of soluble nutrients and chemicals off site
Alley Cropping - Issues
Involves intensive management
May remove land from annual production, depending on the tree crop
May complicate herbicide application
Requires marketing infrastructure for woody plant products
Alley Cropping-Design Considerations
Light requirement for the crop or forage to be grown in the alley way
Root Competition between crops
Type and size of the equipment being used
Tree or Shrub Criteria for Alley Cropping
Marketable
Yields annual or periodic commercial product (wood, nuts or fruit)
Appropriate shade for the alley crop
Minimal roots at soil surface
Adapted to site and soils
Foliage residue does not interfere with alley crop
Growth requirements complement alley crop
Alley Cropping - tropics
fast-growing trees and shrubs established in hedgerows on arable cropland and annual food crops are cultivated in the alleys between the hedgerows.
Hedge prunings are used as soil mulch for fertility and soil improvement rather than for harvest as fodder, fuelwood, or food
Hedgerows are typically spaced 4-10 m apart
History of Alley Cropping
Seen as an alternative to slash-and-burn for the developing world
Basically incorporates an improved permanent fallow phase
slows loss of nutrients add organic matter and nutrients via prunings
History of Alley Cropping
Alley cropping was developed in 1976 at the International Institute of Tropical Agriculture (IITA) in Nigeria
Very attractive to research scientists
easy to design multi-factorial trials of species, spacing, and management.
More research done than for all other agroforestry techniques put together
Main objectives of alley cropping
Improve soil quality
Reduce soil erosion from cultivation on steep slopes
Criteria for Hedgerow Species Selection - Researchers
Minimize competition between trees and crops (light, moisture, nutrients)
looked at variation in root structure and N - fixation (by leguminous tree species)
Synchronized nutrient release and crop uptake
Optimize litter decomposition and nutrient release patterns - affected by quality of litter (C/N ratio, lignin and polyphenols)
Maintenance of soil organic matter
from litter, prunings, root decay and exudates etc.
Nutrient yields from pruning
quantity and quality of biomass produced
Criteria for Hedgerow Species Selection - Farmers
Same as researchers plus…
Impacts on crop yields
Provide alternative harvest products: food, fodder and fuelwood
Labor requirements: quantity and timing of pruning and other management
Hedgerow Biophysical issues
Soil fertility:
Improvement a long term process via SOM build up.
Little direct movement of nutrients from mulch into crops (10-20% of N)
Recycling of nutrients (especially P) insufficient to replenish nutrients removed in harvested crop.
Supplemental fertilizers greatly improve yields in most systems
tree-crop competition highest in low fertility sites and gets worse over time
low P greatly reduces N fixation and hence N input
Hedgerow Biophysical issues 2
Soil fertility contd.
Timing - need to synchronize N release with crop demand
Lignin and polyphenols in mulch slow decomposition
Trade off between rapid N release and weed suppression ability of the mulchLight effects:
Need careful spacing and pruning management to provide canopy closure in fallow period for weed suppression, and cut the canopy back during crop cycle
Alley cropping Performance - short-term yields
Disappointing yields:
improved in 17 of 40 trials investigated including “on-station” trials
Found that alley cropping didn’t work in very dry climates or on infertile soils
Applying small amounts of fertilizer or finding better adapted species may help
no economic incentive to plant trees if fertilizers are very inexpensive
Alley Cropping Performance: Long-Term Yield
Evaluated after long-term interactions have sufficient time to operate (>5 yrs)
criteria–> that yields compared to system without trees increases with time
in 10 out of 12 trials alley cropping led to higher yields
the two failures come from low fert. sites
Alley Cropping Performance - Soil Improvement
Long-term yields strongly dependant on soil improvement
takes at least 3 yrs to detect changes
soil properties improvement usually related to increased SOM
on-station trials in Nigeria, soil C, N, and P increased in proportion to the amount of prunings
From 20 other studies, 50% show large and 25% show moderate improvement
Alley Cropping Performance -Farmers Response
Ultimate test of any agroforestry system is the spontaneous adoption by farmers
Disappointing in the extreme
problems:
increased labor demand
level of skill needed (pruning and it’s timing)
initial loss of yields,
risk
competition for use of prunings - soil mulch, fodder, firewood etc.?
Lessons learned from Tropical Alley Cropping Experience
Difficult trade-offs in farmer adoption
management complexity, loss of cropland, lack of familiarity with pruning, lack of effective farmer education
On-station results may differ from on-farm results
May be better ways to harness the soil-improving qualities of trees - less management intensive?
Lessons learned from Tropical Alley Cropping Experience -2
Need for supplemental fertilizers to maintain yields
Need research on trees adapted to dry systems
Long-term results could outweigh the short-term losses (note: original intent of these systems was to halt degradation). Shown to effectively reduce erosion on sloped land.
What makes a system sustainable?
To continue to meet the goals outlined above the system must:
be sufficiently productive
use resources efficiently – minimize undesired waste
be resilient and adaptable to changing conditions (climate, weather, market, fuel supply, labor availability etc)
How do we know a system is moving towards sustainability?
Need measures of performance or indicators for each goal
Look at trends over time
