by Sally Colby
There’s an official definition for agroforestry, but Richard Straight, lead agroforester for USDA’s National Agroforestry Center, narrows it down to “the intentional combining of agriculture and working trees to create sustainable farming and ranching systems.” Agroforestry can also be described as a set of conservation practices that help provide benefits – provisions as well as protection – at the farm scale. Agroforestry practices focus on each farm and each situation.
Straight explained that agroforestry includes five basic practices, and although the practices are distinct, each one describes the density of trees or the ratio of trees to crops or trees to livestock. “We aren’t talking about taking agricultural land and converting it to forest,” he said. “We’re talking about agroforestry as a form of agriculture that provides some other opportunities for producers.”
Agroforestry puts permanent vegetation on the landscape, which adds conservation value such as improved water quality and wildlife habitat. Both local and producer issues can be addressed through agroforestry, which incorporates several practices including short rotation woody crops, riparian forest bioenergy buffers, alley cropping, forest farming, windbreaks and silvopasture.
“Silvopasture is probably one of the more controversial agroforestry practices because it combines livestock and trees on the same acreage,” said Straight. “Trees in pastures tend to concentrate livestock; cattle congregate in the shade and cause soil erosion and compaction.” While these issues can be problematic, proper intensive management makes the combination workable.
The benefits of silvopasture include improved plant vigor, lower animal stress, reduced wildfire risk and improved wildlife habitat. There’s also potential annual income from grazing, hay, pine straw and hunting, and long-term income from timber.
While it seems counterintuitive to grow crops in the presence of trees, Straight said the combination can work well. “Warm-season grasses – those that do well in full sun – don’t need full sun to meet maximum productivity,” he said. “Some partial shade helps many forages start growing earlier in the growing season, and also impacts the quality of vegetation for forage with higher nutrient content.”
Straight said another benefit of silvopasture is income from forage and/or livestock while waiting for trees to mature. For many landowners, that annual income helps bridge the cash flow gap while waiting for high-value income from tree harvest.
“Producers using silvopasture don’t need to have all pastures as silvopastures,” said Straight. “It’s beneficial to have some pastures that are open to full sun as part of a rotational grazing system so there’s always high-quality forage.” He added that most silvopasture information is based on southern pines, and although there is less information on managing livestock with mixed hardwoods, producers are showing increased interest in hardwood mixes. Straight noted hardwood silvopasture research in Vermont, New York, Pennsylvania and Virginia.
Windbreaks are an important aspect of agroforestry and provide benefits to soil, crops and livestock. “Windbreaks are linear plantings of trees and shrubs that modify the wind speed on the landscape,” said Straight. “Perennial grass strips can act as a wind barrier – anything that interrupts the flow of wind can be considered a windbreak.”
Benefits of windbreaks include reduced energy costs, temperature modification, erosion reduction, pesticide drift reduction, plant protection, snow management, increased crop yields, odor and dust mitigation, wildlife habitat and carbon sequestration.
Windbreak benefits are related to the density of the windbreak, and that density is created by multiple rows or the species selected. “Trees such as hackberry, green ash and oaks may have density during the growing season that will be greater than in winter,” Straight said. “A winter wheat crop may have different protection needs than corn or soybeans.”
Two keys for creating successful windbreaks are familiarity with seasonal wind direction and realizing that one design doesn’t fit every situation. Species, density and landowner needs all influence windbreak location.
A properly designed windbreak can keep snow out of a livestock feeding area and potentially reduce nutrient runoff. Field windbreaks reduce windspeed for the crop, reduce evapotranspiration and protect young seedlings from abrasion from heavy wind. “Windbreaks can help control soil erosion, and spacing between windbreaks depends on the overall purpose,” said Straight. “We can use windbreaks to help deposit snow in a snowdrift, and we can also spread snow across a field to harvest moisture down into the ground for the next year’s crop.”
Alley cropping involves growing an annual or perennial crop in alleyways between the rows of a long-term tree crop. The agricultural crop generates annual income as the tree crop matures. Alley cropping helps diversify a farm operation, reduces erosion while improving water quality, provides crop protection, improves nutrient utilization, enhances wildlife habitat and stores carbon.
Forest farming involves intentional manipulation (managing shade and canopy) to manage a non-timber crop in the understory. Forest-farmed crops include ginseng, goldenseal, a variety of specialty woods, mushrooms and maple sugar. While these specialty crops require a fair amount of research prior to starting to ensure a market, those who take the time to establish a market can profit. Forest farming benefits include improving the economic value of existing forests, providing a more diverse income and increasing cash flow.
Riparian buffers are natural or planted woodlands adjacent to water bodies designed with a combination of trees, shrubs and grasses to protect water resources from non-point source pollution. Benefits include improved water quality, more protection for the aquatic habitat, enhanced wildlife habitat, stream bank protection, a potential income source from timber and specialty products and flood protection.
“We see riparian buffers planted solely as a conservation practice,” said Straight. “We’re seeing some research for harvesting part of the trees in a riparian forest buffer as biomass – harvesting some trees while leaving enough to maintain their function as a buffer.”
Trees planted as a riparian buffer take up phosphorus and nitrogen, which benefits the water supply. However, after trees have taken up significant levels of those elements and leaves drop, stored phosphorus and nitrogen enter the water. This can be a significant issue, so in some cases, harvesting mature trees becomes the solution. Straight added that in riparian areas prone to flooding, harvest may not be an option.
Straight said agroforestry can benefit large farms by helping to mitigate issues such as water quality and nutrient loss. For smaller farms incorporating agroforestry, there’s potential for increased profitability through of high-value specialty crops.