By Diomy S. Zamora, Extension Educator and Professor, University of Minnesota Extension; co-contributors Gary Wyatt, and Mike Reichenback of the University of Minnesota Extension and Dean Current University of Minnesota Forest Resources Department
For years, conventional wisdom among foresters has been to keep the cattle out of the woods if you want to grow high quality timber. There is no question that uncontrolled cattle grazing can tear up a perfectly good woodlot, so can woodland grazing be practiced to benefit trees and animals? In Minnesota, we often see cattle grazing in wooded areas. According to the 2012 USDA Census of Agriculture, there are more than 640,000 acres of unproductive and unmanaged wooded pasture in the state. Opportunities exist to manage grazed woodlands for economic and environmental benefits using silvopasture.
As one of the five agroforestry practices recognized by USDA, silvopasture (the word "silvo" came from the word silviculture (the art of establishing and tending a forest) and pasture, which implies grazing) is the deliberate integration or combination of trees, forage, and grazing livestock operations on the same land. Grazing animals could be cattle, horses, goat, sheep, hogs, and even chickens. The combinations of these components (trees, pastures, and animals) are purposefully managed to provide forage and timber products on a sustained basis. These are not individual practices that occur coincidentally together or are managed independently. The components are functionally combined into a single management unit tailored to meet the landowner's objectives. Silvopastures are intensively managed to optimize the production of the forest products and forages. Science-based grazing, haying, fertilization, tree pruning and trimming and other cultural practices are planned in advance to compliment tree protection, reforestation, market cycles, and work load. Managing forest, pasture and grazing are conducted in harmony so as to enhance the production of multiple harvestable components, while also providing conservation benefits. In silvopasture, the yield of the combination of the products usually exceeds the normal yield of either enterprise individually.
Silvopasture can be established in two ways: establishing pasture in wooded areas or planting trees in pasture. Although still uncommon in the Midwest, silvopasture is big business in other parts of the world. The Dehesa silvopasture in Spain and Portugal covers about 5 million acres. This cultural landscape features oak for cork, acorns for high-value Iberian ham, and fodder for other livestock to graze among the trees. In Finland, Norway, and Sweden, commercially-harvested reindeer graze 100 million acres of managed birch and pine forests?an area nearly the size of California. Silvopastures also are common in the pine plantations of the southeastern U.S.
Benefits to the trees: The practice of silvopasture employs a "crop tree management" approach to forest management. This approach involves identifying the high-quality trees and cutting low-quality neighboring trees to allow opening up of the canopy to facilitate forage growth and to minimize the competition for sunlight, water and nutrients within and among the trees, and forages. Young trees that reach the top of the canopy are generally selected as crop trees. The management of grazed woodland using crop tree management approach in silvopasture can result in high value timber products resulting from thinning, pruning, and managing tree density. Managing the basal area or tree stocking density is key to successful silvopasture practice.
Benefits to the forage: Unmanaged woodland grazing tend to produce limited amounts of forage for cattle. Typically, this forage is composed more of forbs, shrubs, and tree seedlings and less of grasses. The grasses that grow in unmanaged woodlands tend to be lower-yielding cool season grasses. Crop tree management employed in silvopasture can increase forage production because more light makes it to the forest floor. Furthermore, shaded, cool season forage plants can be more nutritious for livestock, and can result in a greater livestock weight gain over animals grazed in pasture alone. After converting five acres of his wooded pasture, into silvopasture, Dan Caughey, a farmer/landowner in central Minnesota, observed that when grasses in the silvopasture were lush, the cows were happy, comfortable, and did not disturb the soil. Conversely, in the heavily wooded pasture, the cows just compacted up the soil with their hooves allowing potential environmental setback.
Benefits to the livestock: Shade provided by the trees in silvopasture can provide a cooler summer environment for livestock and the trees provide shelter during extreme cold conditions during winter seasons. Research shows that livestock growing under silvopasture show increase in weight gain compared to livestock growing in open pasture.
Environmentally, there are greater plant nutrient uptake efficiencies in silvopasture. The deep tree roots coupled with pasture plant roots acquire nutrients from a greater range of soil depths, thus improving water quality. Furthermore, the equal distribution of shade in silvopature system can prevent cows from congregating in one location, thus minimizing soil compaction, and erosion.
Restoring Ecosystem Function
Silvopasture, when well managed, can restore ecological features and functions to farmland. The practice mimics savanna ecosystems, where diverse plant types add habitat for declining savanna species like the red-headed woodpecker and the whippoorwill. Often found in transition zones between forest and grassland biomes, savannas include trees, shrubs, and a diversity of shade-tolerant grasses and forbs. By some estimates, oak savanna once covered 50 million acres of the Midwest. As such silvopasture can be a tool for restoring native savanna structure to degraded farm woodlots. Silvopasture is also seen as an approach to eradicate invasive species as well. There is now a growing interest in using goat-silvopasture to eradicate invasive species such as buckthorn and honeysuckle. Silvopasture takes its cues from an ecosystem that works with our landscape and climate, adapting form and function to accomplish agricultural goals.
Silvopasture is new to Minnesota. For those who are grazing a woodlot, silvopasture can be applied to increase animal and forest production. Crop tree management employed in silvopasture can increase yields of both forage and high-value timber. To gain the maximum benefit from this system while reducing the impact of the grazing on tree health, it is best to use a rotational grazing system limiting the amount of time the animals are in the woodlot. Adequate rotational grazing is key to the success of the system and to ensure tree regeneration. Silvopasture is not appropriate when:
- forest cover casts a deep shade preventing grasses from growing
- soils are too wet and slopes are too steep
- the sites have sensitive flora
- there are young trees that need protection
- you cannot guarantee that grazing will be well-managed.
There is still much to be done to see more widespread adoption of silvopasture in Minnesota, but if properly applied and managed, it has the potential to promote sound management, increase productivity, and reduce environmental degradation in woodlots that are currently being grazed.