Silvopasture: Integrating Agriculture and Forestry

by Alan Franzluebbers, USDA Professor of Soil and Crop Sciences at NC State University and Coordinator of CEFS’ Farming Systems Research Unit

Some landscapes are difficult to manage with contemporary agricultural techniques that are designed for uniformity of production. Researchers at the Center for Environmental Farming Systems’ Field Research and Outreach Facility at Cherry Farm in Goldsboro, NC discovered this when they tried to grow corn and soybean in rotation on a floodplain site that had a wide diversity of soil texture and slight variations in elevation. During the first several years, yields were either drought-affected on the sandy hummocks and acceptable elsewhere, or decimated in low-lying areas due to flood waters and excessive moisture that rotted crop roots.

Fortunately, with the vision of Dr. Paul Mueller, retired Professor of Crop Science at NC State University and one of CEFS’ founders, the site was also planted with rows of trees to create a mixture of agriculture and forestry. Once trees became large enough to be pruned of their lower branches and allow people and animals to move under them, investigators transitioned the site from alley cropping to silvopasture – the intentional mixture of trees and pasture.

Why would good agricultural land be planted to trees and then to pasture? The answers come from recognizing that not all agricultural landscapes are able to withstand the weather extremes in North Carolina equally well. A portion of agricultural lands that are considered marginal for production may be ideally suited for silvopasture. Floodplain soils have deposits of coarse sand. These soils don’t hold water very well if tilled, resulting in loss of organic matter; additionally, they don’t hold water long enough to withstand frequent occurrences of 10+ days without precipitation in the summer. The result is drought and crop loss.

Other areas of the floodplain have soils with fine-texture (i.e. gummy clay) that have poor infiltration and remain saturated for long periods of time – again, a consequence of tillage. This accelerates soil organic matter decomposition and disturbs the continuity of pores for drainage to occur. Trees are able to withstand both drought and water-logging much better than annual crops due to their deep and expansive root system once established. It also helps that the large demand for water by trees creates an effective wick to dry soils out when wet. The perennial and deeper rooting of trees allows them to search out water deeper in the soil profile when necessary. In a similar manner, pasture grasses develop a perennial root system, which penetrates deep into the soil to extract water and overcome periods of drought. They can also withstand occasional water saturation by growing rapidly and transpiring water back into the atmosphere.

The alley-cropping experiment that Dr. Mueller initiated in 2007 is now a fully functional silvopasture experiment due to the dedicated support and effort of the Cherry Research Farm staff. Research will allow us to answer questions about the types of management that will be most beneficial to producers, and how management of silvopastures affects basic agronomic characteristics of plant mixtures and environmental quality issues important to agricultural stakeholders and the public.

The experiment at CEFS’ Field Research site now has a combination of several native species including loblolly pine, longleaf pine, and cherrybark oak trees. Native warm-season grasses include big bluestem, eastern gamagrass, indiangrass, and switchgrass. The only non-native introduction at this time is beef cattle – Black Angus heifers that graze the forage during the summer in the protection of the shade offered by the trees.

Our core team of principal investigators and students will be able to study (a) soil biogeochemical cycling of carbon and other nutrients, (b) biophysical attributes of temperature, water, and light, (c) nutritional analyses and botanical dynamics of native warm-season grasses, (d) animal production, behavior, and stress responses, and (e) ecological interactions of timber, forage, and livestock components with soil and climatic factors.

Many questions remain for us to answer: How does the system’s configuration affect production and ecological responses? How does grazing management impact forage and timber components and their interactions? How do management and environmental conditions affect productivity? How best to achieve sustainability?

The practice of agroforestry could and should become a more important ingredient in conservation agricultural systems, particularly in North America where its use is still minimal. Without soil disturbance under trees, sequestration of soil organic carbon and nitrogen is possible, water infiltration is enhanced, and soil erosion can be minimized. By creating semi-natural habitat under strips or randomly located trees, biodiversity of agricultural regions can increase. The widespread and deep roots of trees can extract nutrients to avoid leaching losses. Ultimately, trees can be harvested for pulpwood, timber, or biofuel feedstock.

Soil physical and chemical quality under trees in an agroforestry system can be greatly improved, leading to localized benefits at the trees’ edge, and also to regional benefits due to hydrologic alterations and creation of biodiversity habitats and corridors. Enabling an understory of forage can lead to increased numbers of insects and various arthropods, as well as greater bird density and diversity than neighboring monoculture cropland fields. Nutrients can be effectively scavenged deep in the soil profile.

Silvopasture design and management are really only beginning in North America. The potential appears very high for achieving positive environmental results to stabilize agricultural landscapes and build resiliency to climate change. One key to successful implementation on a larger scale will be to demonstrate the potential economic profitability of this management system compared with current agricultural systems, while promoting the potentially larger environmental benefits.

For more information about CEFS’ Agroforestry experiment, please visit the Agroforestry page.