Overstory #36 - Silvopasture: An Agroforestry Practice
The last edition of The Overstory introduced the integration of animals as a key component in forestry and agroforestry systems. This edition introduces the specific case of integrating livestock and forestry, called "silvopasture." The following article has been adapted from a technical note published by the U.S. Department of Agriculture's National Agroforestry Center. Further information and references are found following the article.
Silvopasture as an agroforestry practice is specifically designed and managed for the production of trees, tree products, forage and livestock. Silvopasture results when forage crops are deliberately introduced or enhanced in a timber production system, or timber crops are deliberately introduced or enhanced in a forage production system. As a silvopasture, timber and pasture are managed as an integrated system.
Silvopastoral systems are designed to produce a high-value timber component, while providing short-term cash flow from the livestock component. The interactions among timber, forage and livestock are managed intensively to simultaneously produce timber commodities, a high quality forage resource and efficient livestock production. Overall, silvopastures can provide economic returns while creating a sustainable system with many environmental benefits. Well-managed silvopastures offer a diversified marketing opportunity that can stimulate rural economic development.
Before new silvopastoral systems are established, implications of merging forestry and agricultural systems should be explored thoroughly for economic and environmental considerations along with local land use, zoning, cost-share program and tax regulations. Environmental requirements (e.g., planting trees, stream-side protection, wildlife habitat maintenance) also may vary with land use.
When making tree and forage crop selections, consider potential markets, soil type, climatic conditions, and species compatibility. The timber component should be:
- high quality
- fast growing
- drought tolerant, and
- capable of providing the desired products and environmental services.
Select and use trees and planting/harvesting patterns that are suitable for the site, compatible with planned silvopastoral practices and provide desired economic and environmental returns.
The forage component should be a perennial crop that is:
- suitable for livestock grazing
- compatible with the site (soil, temperature, precipitation)
- productive under partial shade and moisture stress
- responsive to intensive management, and
- tolerant of heavy utilization.
Potential livestock choices include cattle, sheep, goats, horses, turkeys, chickens, ostriches, emu, rhea or game animals such as bison, deer, elk, caribou, etc. The selected livestock system must be compatible with tree, forage, environment and land use regulations. In general, browsing animals such as sheep, goats or deer are more likely to eat trees while large grazing animals such as cattle or elk or more likely to step on young trees. Younger livestock are more prone to damage trees than are older, more experienced animals. Livestock are more likely to impact broadleaf trees than conifers.
Design and Establishment
Silvopastures can be established on any land capable of simultaneously supporting tree and forage growth. However, silvopastoral systems can require a relatively large land base to sustain timber and livestock production continuity. A source of local technical assistance is essential to develop a silvopastoral system matched to local conditions and landowner objectives.
Appropriate establishment methods depend on:
- woodland/forest type (e.g., site conditions, and tree species, age, pattern and spacing) or existing pasture situation;
- whether even-aged or uneven aged forest stands are anticipated; and
- landowner objectives (e.g., timber products, environmental benefits, wildlife, etc.).
Tree pattern is an important factor for silvopasture success. Trees can be evenly distributed over the area to optimize growing space and light for both trees and forage. Alternatively, grouping trees into rows or clusters concentrates their shade and root effects while providing open spaces for pasture production. Trees are typically pruned to increase light penetration and develop high-quality sawlogs.
A successful silvopasture requires understanding forage growth characteristics and managing the timing and duration of grazing to avoid browsing of young tree seedlings. Livestock should be excluded from tree plantings during vulnerable periods. Improper management of silvopastures can reduce desirable woody and herbaceous plants by over-grazing and soil compaction. Thus, intensive management of livestock grazing is the key to success.
Available management tools include:
- tree harvesting, thinning and pruning
- fertilization to improve both forage and tree production
- planting legumes for nitrogen fixation and forage production
- multi-pasture, rotational grazing
- rotational burning
- supplemental feeding
- developing water sources (e.g., stock tanks, windmills, photovoltaic pumps, hydraulic rams, ridge reservoirs, etc.) * locating salt/mineral licks and walkways to encourage uniform livestock distribution
- fencing (e.g., standard or electric), tubing, plastic mesh, repellents, and seasonal livestock exclusion to reduce damage to young seedlings
Benefits of Silvopasture
Integrating trees, forage and livestock creates a land management system to produce marketable products while maintaining long-term productivity. Economic risk is reduced because the system produces multiple products, most of which have an established market. Production costs are reduced and marketing flexibility is enhanced by distributing management costs between timber and livestock components.
Comprehensive land utilization in silvopastoral systems provides a relatively constant income from livestock sale and selective sale of trees and timber products. Well-managed forage production provides improved nutrition for livestock growth and production. Potential products of the tree component include: sawtimber, veneer logs, pulpwood, firewood, pine straw, posts and poles, harvested game, nuts, fruit, ornamental flowers and greenery, tree sap products, mushrooms, organic mulches, and other secondary products.
Woodland and Forage Benefits
Grazing can enhance tree growth by controlling grass competition for moisture, nutrients and sunlight. Well managed grazing provides economical control of weeds and brush without herbicides, maintains fire breaks and reduces habitat for gnawing rodents. Fertilizer applied for forage is also used by trees. In addition, livestock manure recycles nutrients to trees and forage.
Some forage species tend to be lower in fiber and more digestible when grown in a tree-protected environment. Trees that provide shade or wind protection can have a climate-stabilizing effect to reduce heat stress and windchill of livestock. Protection from trees can cut the direct cold effect by 50 percent or more and reduce wind velocity by as much as 70 percent. Livestock require less feed energy, so their performance is improved and mortality is reduced.
Environmental and Aesthetic Benefits
Silvopastures can increase wildlife diversity and improve water quality. The forage protects the soil from water and wind erosion, while adding organic matter to improve soil properties. Silvopastures provide an attractive landscape with an aesthetically pleasing "park-like" setting. In contrast to concentrated livestock operations, silvopastoral systems are less likely to raise environmental concerns related to water quality, odors, dust, noise, disease problems and animal treatment.
Ned B. Klopfenstein, W.J. Rietveld, and Richard C. Carman, USDA Forest Service National Agroforestry Center, Lincoln, NE; Terry R. Clason, Louisiana Agricultural Experiment Station, Homer, LA; Steven H. Sharrow, Oregon State University, Corvallis, OR; Gene Garrett, University of Missouri, Columbia, MO; Bruce E. Anderson, Dept. of Agronomy, UNL, Lincoln, NE.
Rowan Reid and Geoff Wilson, 1985. Agroforestry in Australia and New Zealand, Goodard and Dobson, 486 Station Street, Box Hill, Victoria 3128, Australia.
Related Editions to The Overstory
- The Overstory #50--Animal Tractor Systems
- The Overstory #48--Farm Forestry
- The Overstory #37--Trees/Livestock Examples
- The Overstory #35--Animals in Agroforestry