Silvopasture works with landscape, climate to meet farming goals
By Keefe Keeley, Savanna Institute
Although a subject of contemporary agricultural science, silvopasture has timeless roots. The word comes from the Latin silva for forest, or the Roman deity Silvanus, known for protecting woodlands, fields, and flocks of livestock. Aptly enough, silvopasture integrates these very elements of the farm.
In more recent history, USDA scientist J. Russell Smith researched the value of trees in agricultural systems. The first half of his classic volume Tree Crops is devoted to the use of trees in livestock production. Silvopasture—the integration of livestock, pasture, and tree crops—offers a modern method to achieve Smith’s vision of trees providing for human needs while sustaining the land. The USDA considers silvopasture one of five practices within the field of agroforestry, and define the practice as “intentional combinations of trees with livestock which involve intensive management of the interactions between the components as an integrated agroecosystem.”
Not to be confused with the tree-like Ents of Tolkien’s Middle Earth, these four “Ints” distinguish silvopasture and other agroforestry practices from other farming methods:
■ Intentional combinations of trees, livestock, and forage for their mutual benefit;
■ Intensive management of land, fertility, grazing, water, and other farm features;
■ Interactive relationships among tree, livestock, and
■ Integrated function in a single management unit, including both farm and forest production as well as amenity values such as wildlife habitat, water quality, and soil conservation.
Although still relatively uncommon in the Midwest, silvopasture is big business in other parts of the world. Dehesa silvopasture in Spain and Portugal covers about 5 million acres (one-seventh the area of Wisconsin). 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.
Silvopastures mimic or modify the workings of natural ecosystems for farm purposes. Just as management-intensive rotational, ultra-high stock density, and patch-burn grazing practices mimic the way wild herds and grassland ecosystems work, silvopasture mimics a savanna ecosystem. 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. The Driftless Area, for example, was recently determined to have been about 70 percent oak savanna prior to European settlement. Silvopasture takes its cues from an ecosystem that works with our landscape and climate, adapting form and function to accomplish agricultural goals.
Silvopasture in Practice
Like any farming practice, planning is key to successful silvopasture. What are your goals? How will silvopastures fit into your existing systems for watering, fencing, and providing shade and shelter? Will the tree, forage, and livestock combinations you have in mind be a good fit? What are your time, budgetary, and knowledge constraints? Addressing these questions will help determine if silvopasture is a good fit for your farm, and what steps you need to take to establish and manage it.
Put most simply, silvopasture can be established in two ways: planting pasture in trees or planting trees in pasture.
Between 30 and 70 percent cover is often the goal for silvopastures. A tree canopy denser than 70 percent will stifle forage growth, and one sparser than 30 percent risks livestock congregating around too few trees.
In existing woodland, forestry techniques can be used to achieve desired tree canopy cover. Use crop tree management: identify the high-quality trees and cut low-quality neighboring trees that compete for sunlight, water, and nutrients. Young trees that reach the top of the canopy are generally selected as crop trees. But, in silvopasture applications, timber value and potential for growth may not be the only measures of quality. Filtered shade, forage value of fruit and foliage, shelter value of evergreens, or strategic location for afternoon shade, aesthetics, and wildlife habitat also should be considered.
Once you’ve thinned to your desired canopy cover, you may decide to plant forages under the trees. Some farmers like to do this to ensure forage production, while others say it’s not worth the time and expense, especially on the edge of open pasture where pasture grasses and forbs can come in on their own. I recently started a research project where after thinning the tree canopy, we’re comparing a domestic seed mix, a native savanna species seed mix, and a control without any seeding. We are measuring plant diversity, establishment success, forage quantity, quality, and utilization, so stay tuned for the results.
When planting trees into open pasture, your goals and circumstances will dictate what is best for your farm. You should consider where to plant the trees, what species and age of trees to plant, how to prepare the site for tree planting, how to manage competing vegetation once trees are planted, and how to protect young trees from livestock and wildlife pests. Research in the Midwest to help you make these decisions is scant, but here’s what I recommend.
When deciding where to plant, aim for uniform shade in each paddock to keep livestock from congregating in one spot. Planting trees all along the western edge of paddocks will provide shade in the afternoon when animals need it most. The filtered shade from trees like locust, walnut, and poplar will allow more grass growth than trees like maple with dense canopies. A diversity of trees can provide multiple functions, a succession of harvests, and insurance against selective pests. On the other hand, when you alternate different tree types you risk having the fast-growing species overtop and suppress their neighbors.
In general, older trees cost more and are more work to plant, but take less maintenance and provide their benefits sooner. Younger trees are more affordable, and you can put hundreds in the ground in a day with a tree planter—I know of a farmer who planted 12,000 trees in a day!
Preparation of the site should address weed, soil, and drainage issues.
Tillage, repeated mowing, stale seedbeds, or temporary row covers can all be used for weed control prep. Ideal soil conditions vary by tree species. For example, many trees and shrubs are susceptible to iron chlorosis in alkaline soils, so liming may not be advisable. A single-shank subsoiler or keyline plow can work wonders for root penetration and water infiltration, but if you plant into the trench, back fill soil thoroughly around roots, or plant your trees just up- or downhill of the trench. Roots in large air gaps cannot absorb water and nutrients, and the trench can make a nice home for rodents that eat tree roots and bark.
Once trees are planted, their growth and survival will be enhanced by managing competing vegetation. (Although it is worth noting that some people swear by “hiding” their trees from deer by letting weeds grow up). Depending on your fencing system and what type of livestock you have, animals can help control plant competition close to your young trees. Chickens can help keep weeds down if you fine-tune the stocking rate. Cattle will graze up to the base of the tree row behind a single strand fence the right distance away. An occasional pass with a weedwhip also gives trees a head start.
Mulch can also be used to manage competing vegetation, but not all mulch is created equally. Conifer chips encourage brown rots, which can cause problems for deciduous trees. Hardwood chips foster white rots, which devour lignin and leave a lot of cellulose behind, a boon for the soil and its denizens. Mulch from small diameter branches, known as ramial wood, contains more nutrients and a lower C:N ratio than log wood. This is important for fertility.
You can also grow weed suppression by planting rows of protector/N-fixer/trainer/browse trees and shrubs adjacent to the trees you want to grow up straight and tall. In this arrangement you are creating a hedge with a sheltered inner row bordered by outer “dinner” rows.
Protecting trees from animal damage can make or break a young planting. Population irruptions of insect pests like Japanese beetles occasionally wreak havoc, but with trees, your main challenge is mammals—livestock, deer, and bark-devouring rodents. Protection methods run the gamut: all manners of row or perimeter fencing (including electric baited with peanut butter), steel cage fortification (such as hog panel or chicken wire), tree tubes (such as those sold by Southwest Badger RC&D), wire mesh or plastic spiral base guards (essential where there is heavy vole pressure), odor repellents raptor roosts and owl houses, and farm dogs and cats. What works best on each farm will vary. Since protection is often one of the most critical and costly parts of planting trees, it pays to find what works, and to not do more than necessary. There is no substitute for experience—I often advise farmers to start with a test plot to experiment with different methods of tree protection.
Livestock, Pasture Performance
Silvopasture can offer improved livestock and pasture performance, added income from forest crops, and restored ecological functions.
Livestock performance in silvopasture systems has been a key issue for researchers. University studies in Kentucky, Missouri, and Arkansas have all shown increased weight gain in beef cattle that have access to shade. Studies in Florida and Virginia have shown increased milk production from cows that have shade. Two other studies in Florida and Missouri observed nearly twice the conception rate in beef cattle with shade compared to those without.
Production losses due to heat stress can begin at temperatures as modest as 78 degrees Fahrenheit. The University of Missouri has a smartphone app called Thermal Aid that helps assess signs of heat stress in your herd. Learn more about the app at thermalnet.missouri.edu.
Winter shelter can also impact livestock performance. Animals without adequate shelter in winter require more feed to maintain body condition.
Pasture performance has also been the subject of silvopasture research, testing how trees within pastures affect forage quality, quantity, and availability. One potential benefit of silvopasture is a less drastic slump in forage yield during summer months. Decreased production in shaded pastures during the spring flush can be a small price to pay for paddocks that continue to grow later in the year when open pastures go dormant.
It may not just be shade that keeps the grass green under trees during heat spells and droughts. Through a process called hydraulic lift, some deep-rooted trees actually bring water up from lower soil horizons, where it is used by neighboring plants. Although no one has reported hydraulic lift occurring in silvopastures, it has been documented in potential silvopasture tree genera such as pine and oak. Moisture retained from slower snow melt can also impact seasonal forage growth in silvopastures.
Studies have also shown improvements in forage quality under partially shaded conditions. Researchers at Iowa State showed in vitro digestible dry matter was 3-5 percent greater for grasses grown under partial shade, compared to those grown in full sun. Another study in Missouri showed higher protein and lower fiber content in annual ryegrass and cereal rye grown under a pine and walnut canopy, compared to treeless pasture controls. This study also showed that, although cumulative forage production over several years was reduced by about 20 percent in the silvopasture, beef heifers grazed in the silvopasture showed no difference in gains than animals in the open pasture controls, likely because the silvopastures grew forage of better quality.
Many of these studies are from hotter parts of the country, where heat stress and summer pasture slump are more serious concerns. The climate extremes we are increasingly subject to in the Upper Midwest suggest that we might do well to take lessons from folks in warmer, drier places.
Growing trees with long, branchless trunks to make high-value saw logs can be a challenge in silvopastures, given the partially open canopy. In natural forests and plantations, shade from neighboring trees inhibits branching. That said, after a thinning, large dominant trees grow fewer new branches than young and overtopped trees. Some research has shown that crop trees retained when establishing silvopasture maintain their timber value, and even increase their growth rate.
As previously mentioned, trees planted for timber can also be trained to straight branchless growth via interplanting with fast-growing “nurse” trees. These nurse trees can be harvested early for many purposes, from pulp to firewood to mushroom inoculum. Leguminous nurse trees can also fertilize crop trees while being coppiced or browsed for fodder. Many “weed” trees like locust, box elder, and mulberry have leaves of high forage quality, making them potential candidates for the “dinner” rows of a hedge that protects and trains inner timber rows.
Silvopastures can also integrate human food production with fodder for livestock. Orchards that pasture fowl early in the season to eat insect pests or hogs to clean up after fruit harvest exemplify this stacked enterprise strategy. It is important to be aware of food safety regulations regarding livestock use and wastes where produce is grown, while also recognizing the potential of livestock as a tool in orchard sanitation and vegetation management.
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 specialists like the redheaded woodpecker and the whippoorwill. Some of my ongoing research is testing silvopasture establishment as a tool for restoring native savanna structure to degraded farm woodlots. Besides biodiversity benefits, other potential gains in silvopasture ecosystem functions can be realized in nutrient cycling, soil conservation, carbon sequestration in trees and soil, improved soil hydraulic function, and water quality.
Not all trees in pastures restore ecosystem function. A few trees by a creek where dozens of cattle congregate and erode the riparian area will not restore anything. Likewise, continuous access to woods will just lead to compacted soil, sick trees, and diminished wildlife and plant diversity. Without adaptive planning and management, these are not actually even examples of silvopasture.
Turning livestock out into a single pasture for the season does not qualify as managed grazing, and by the same token simply giving livestock access to the woods or having a couple of trees in the pasture does not count as silvopasture. Mismanaged livestock have a long history of degrading prairies, savannas, forests, wetlands, and riparian areas. For example, studies have shown that decades after farmers started excluding livestock from hillsides in the Driftless Area the improved water infiltration has increased flow rate from springheads, which has helped restore trout habitat.
Silvopasture is not a fancy word to excuse abuse of healthy natural areas. It is a method of intensive management that integrates trees to profitably raise livestock and care for the land.
Visit our website www.savannainstitute.org to see examples of farms practicing silvopasture and other savanna-mimicking farming techniques. Get in touch to join in these efforts.
Keefe Keeley is the executive director of the Savanna Institute, a nonprofit that carries out case studies of savanna-based agriculture across the Midwest. He has a master’s degree in agroecology from the University of Wisconsin.
From the November | December 2015 Issue