Marrying cows, grass, and trees

On most grazing operations, woodlots are separated from pastures and cows in the same way that bird dogs typically aren’t housed with the chickens. The latter will probably never change, but the former is.

More and more grazing operations are starting to mesh trees with pasture and livestock, a system referred to as silvopasture. Janet Steele, a forestry and wildlife extension agent with Clemson University, and Liliane Silva, Clemson’s extension forage specialist, note that this shift is taking place as farmers look to boost plant biodiversity, enhance soil health and livestock productivity, and add to enterprise revenues.

“Silvopasture systems can be created either by thinning existing timber stands or by planting trees in existing pasture or in newly established areas,” the extension specialists note. “The choice of forage should be considered based on local climate and topography conditions, soil type, and operational goals, among others.”

Developing a silvopasture system requires proper planning and understanding of the needs and requirements of each component of the system — forage, livestock, and tree — and their interrelationships with the ecosystem.

A new beginning

New tree stands can be established on fallowed agricultural land, hayfields or pastures, or cutover timberland. Depending on the site type, preparation will vary to help ensure healthy tree establishment. For example, pastures and hayfields will need to be cut or grazed close to the soil before trees are planted. In crop fields, ripping or subsoiling may be needed to eliminate any severe soil compaction. For all sites, a herbicide application may be needed to control competition from grasses, broadleaf weeds, and woody vegetation.

If planting into a former crop field, account for any herbicide carryover from previous applications. A site might have to be fallowed for a year before planting tree seedlings. Another pre-establishment consideration is soil pH, which may need to be adjusted for the tree species selected.

Silvopasture systems in the Southeast utilize pine species. In South Carolina, this is most often longleaf or loblolly pine. In other regions, different tree species are more adapted. The Clemson specialists offer two planting designs. One is to plant a double row of trees in an east-west direction with a forage alley between rows. This will help ensure optimum sunlight interception for the forage strip.

Tree seedlings are planted with 8 to 10 feet between the twin rows and 4 to 8 feet between trees within rows. There is usually a 30- to 40-foot alley between the sets of rows. This design results in 200 to 400 trees per acre.

Another planting option is called wide-block planting. For example, planting trees in a 12-foot by 12-foot spacing, which results in having about 300 trees per acre. This design limits the ability to harvest hay. With this system, the specialists recommend using genetically improved tree seedlings that have fewer limbs and improved stem form. Exclude livestock from new stands for the first three to six years. Terminal tree buds need to be above browsing height before grazing, and trees need to be sturdy enough to withstand rubbing and trampling prior to animals being introduced.

Existing woodlot

The other method for establishing the tree component in silvopasture is to manage an existing timber stand. Often, an existing woodlot needs to be thinned to allow adequate sunlight to reach the floor for successful forage establishment and production.

If the stand is being thinned for the first time, this is traditionally a third or fourth row thinning, with additional removals within the residual rows. Use a professional forester to mark subsequent thinned trees, ensuring the remaining crop trees have the best timber quality while also meeting stand density requirements. Depending on the producer’s selected forage, a residual basal area of 40 to 60 feet per acre is usually recommended.

Management of the tree component in a silvopasture system may include a prescribed burn to reduce hazardous fuels, improve the forage sward for livestock and wildlife species, and help prune lower limbs. Mechanical pruning is a labor-intensive activity required to maintain stem quality on the crop trees and create knot-free wood. It also raises the canopy to allow more sunlight to reach the forage base. Herbicide applications are often required on the understory of the timber to enhance forage production.