Creating Silvopastures: Some Considerations When Thinning Existing Timber Stands

Silvopastures intentionally integrate trees with forage and livestock production in a rotational grazing system. These systems have the potential to improve animal comfort, increase farm resource use efficiency, boost income, and mitigate environmental costs. From a theoretical standpoint, silvopastures are designed and managed to capture the beneficial interactions among each of the system’s components. The added biodiversity and buffering (e.g., reduced temperatures and water runoff) provided by integrating trees and forages can also increase system resilience to extreme weather events and a changing climate. For the growing number of folks interested in silvopastures the benefits of these systems seem clear, but the path to creating silvopastures may be less certain.

The quickest way to create a silvopasture is to thin an existing tree stand and then establish forages (fig. 1). Producers might prefer this way because it more quickly increases their forage/grazing capacity and shortens the investment time, but several issues should be considered before taking this approach. Soils and slope, tree stand composition and age, returns and costs for thinning the trees and clearing residues, and the method of establishing forages are all important variables when considering whether to thin existing stands.

Build a Team, Make Goals, Assess Resources, and Plan, Plan, Plan

Given that few producers (or professional consultants) have experience across both forage-livestock systems and forestry, the first recommendation for getting started should be to build a team. Extension agents, foresters, and technical service providers (from the Natural Resources Conservation Service or soil and water districts) working together can assist in considering goals, site suitability, implementation strategies, and best management over short- and long-term time horizons. Silvopasture development involves significant investment, requires a long-term view, and is not changed rapidly once set in place, so careful preparation is essential. Having a team working together to help to get it right on the front end can minimize mistakes and improve outcomes.

It is worth noting that many natural resource professionals who are unfamiliar with these integrated systems are resistant or reluctant to support their adoption. They might view creating silvopastures by thinning woodlots as detrimental to both the environment and the health and productivity of the forest. This view is likely due to the fact that (1) this thinning involves reducing rather than increasing tree density/cover, (2) unmanaged livestock often damage trees, and (3) in some stands, thinning will lead to decreased biodiversity or loss of some nontimber forest species. These concerns have a valid basis given historical mismanagement. The resource professional’s perspective and expertise is valuable and their support is best obtained by including them in the process early and ensuring them of your commitment to long-term, engaged, and active management. Seek their input to help make short-, medium-, and long-term management plans that safeguard the health and vigor of the remaining trees.

Site Suitability

On many farms, the back woods are the back woods because they are often on marginal land. Attempting silvopastures on such sites is a poor decision if the ground cannot be readily managed, is highly erodible, or will not support adequate forage production.

Unfortunately, too many farms currently allow cattle unmanaged access to woodlots, resulting in severe damage to soils and vegetation and creating opportunities for non-native invaders. In some cases, developing silvopastures from abused woodlots can provide a functional way to advance responsible, productive land management through timber stand improvements, invasive species removal, and soil revegetation. Of course, this will require a great step up in management, including time and labor.

Harvest Decisions

Deciding which trees to harvest can be a challenge, especially in hardwood stands. Tree species, form, size, age, local markets, value, and timber quality all play a role in the current and future returns to the system. These factors also affect their suitability when managed with forages and livestock. Along with these considerations, thinning decisions should account for farm layout and infrastructure associated with rotational grazing system needs which don’t always match the preferred harvest plan.

Knowing how much timber to remove (and when) can be perplexing, yet sound thinning decisions are essential both for tree development and for light management for forage productivity. Silvicultural principles such as relative density and stocking should be considered to ensure the thinning achieves the most productive and healthy outcome. Removals based on basal area and number of trees using forestry stocking charts can help identify a reasonable balance point for getting adequate light to the forages without compromising the long-term productivity and health of the tree stand. Thinning factors will differ from stand to stand based on characteristics such as average tree diameter, species composition, topography and environmental sensitivities, site productivity, and operational considerations. For instance, small diameter trees can be thinned to a much greater extent without risk of windthrow and top breakage.

However, heavy thinning could be too stressful if those trees remaining after harvest are tall, thin, and top-heavy or prone to epicormic sprouting (fig. 2). Such trees would be susceptible to damage from high winds or ice. In some cases, multiple thinnings over time could be best for the tree stand, but this approach must be balanced against greater costs, slower conversion, and the potential for more damage to soil and remaining trees from harvest operations. In any case, forestry professionals can and most often should assist this process.

Some Economic Considerations

Working with a professional forester is likely to improve the functioning of the final system and also benefit you financially. Consulting foresters are well- suited to not only provide input into thinning but also to assist in marketing the timber. In general, timber sales involving a consulting forester have greater economic return (due to competitive bidding) and have stronger contracts to ensure minimal damage to the site and protect landowner interests.

Producers looking to support conversion to silvopastures by selling the harvested timber could be disappointed if their woodlots suffer from past high-grading (i.e., “taking the best and leaving the rest”). This all-too-common practice (fig. 3) has been used to maximize short-term timber returns, but it often leaves low-value and low-vigor trees and does not fit with a long-term strategy of improving the timber stand. Such sites will have even less economic value if they have been subjected to unmanaged livestock access. Stands such as this, regardless of future use goals, could benefit from a “start-over” type of strategy, such as clearcutting and planting.

Stumps, Timber Harvest, Residue Management, and Forage Establishment

Residual tree stumps can be problematic to work around. Setting stump height limits and penalties for those trees not meeting this standard can be useful, although setting strict limits for timber harvest could reduce the price received for the harvested timber. If future management will not include large machinery, strict limits on stumps or harvest residues might not be necessary.

In sparse tree stands, removing residue might not be justifiable or necessary (fig. 4). However, residue management typically will be needed postharvest and often can be performed by the logger in lieu of payment. Residue can include tree branches and treetops that were not removed as part of the logging job. Cleanup could be as simple as pushing the remaining wood into piles and burning or removing these materials by mulching. Forest mulching is also a good way to remove standing small-diameter junk wood without causing excessive soil disturbance, although it can affect germination and growth of the forage to be established (see “Options for Clearing Land: Pasture Establishment for Horses,” Virginia Cooperative Extension publication 465-341 [http://pubs.ext.vt.edu/465/465-341/465-341.html], for more on forest mulching). Removing scrubby underbrush before the actual harvest can be helpful if costs are not prohibitive. Some producers successfully use small ruminants as “brush cutters” for this purpose as well as for cleaning up stump sprouts after thinning.

In most cases, reducing residues and heavy duff layers (mechanically or with fire) will be essential for successful forage establishment (figs. 5-7). High seeding rates could be needed because litter and mulch layers reduce seed contact with mineral soil, greatly decreasing germination and establishment. This is especially true when broadcasting seed, which might be the only suitable method of seeding forages into thinned tree stands. High levels of carbon-rich, low- nitrogen woody debris and residues left from logging can lead to a “tie up” of nitrogen and other nutrients by soil microbes, limiting forage growth. Some producers have success confining and feeding hay to livestock on sites where they wish to establish forages. This takes advantage of browsing, “treading action,” and additions of fertility in feces and urine but may be less useful (or require more time) when converting large land areas. Producers should also consider the time of seeding to minimize leaf fall effects on young seedlings. (e.g., on sites with stands of oaks or other trees with heavy leaves, seeding after leaf drop could be advantageous to avoid smothering emerging seedlings provided that adequate seed-soil contact is maintained. In all cases, creating a sound forage stand is essential both to the grazing system and to ensure future erosion risks are minimized.

Soil Fertility

Soil sampling is a critical first step in understanding forage production potential and input needs for silvopasture created in woodlots or forest stands. Many forest soils have low pH and fertility. Achieving adequate pH and nutrient levels (primarily phosphorus and potassium) suitable for good forage production might be difficult logistically, economically, or both. When such amendments are needed, low-cost organic nutrient sources such as biosolids or poultry litter are likely to be among the most cost-effective options if the site can accommodate spreading equipment.

If available, applying lime-stabilized biosolids is an effective way to increase soil pH while also supplying phosphorus and nitrogen to the soil. If waste wood remains after thinning, this can be burned and the residual ash spread on-site because the ashes can be a useful source of potassium and other minerals.

Forage Species and Grazing Management

Several forage species can be effectively established and managed in silvopastures. Most cool-season forage grasses are reasonably shade-tolerant, and orchardgrass, as the name implies, is one of the best. In southern pine silvopastures, both introduced (e.g., bahiagrass and bermudagrass) and native grasses (such as switchgrass, Indiangrass, and bluestems) are considered suitable species, but more light (greater thinning) may be needed to sustain these grasses. Legumes are generally less-tolerant of shaded environments than grasses. However, there is a broad range in adaptation among grass and legume species and varieties, although there has been little effort to compare and select for shade tolerance in forages. The pattern of forest thinning can further play a role in the suitability of forages for the site and their ease of management in grazing systems (fig 8).

Whatever the forage, rotational grazing management is essential for silvopastures. The greater the amount of shading, the longer the rest period needed for forage plants to recover. Similarly, less intense grazing than is typical for open pastures can help maintain stands growing in deeper shade (fig 9). That is, in these more light-limited environments, forages should not be grazed as close to the ground as would be acceptable in open pastures. This will also help protect trees from potential damage associated with compaction and nutrient loading, as often happens when livestock have unmanaged access to forests and wood lots.

The Take Home

Silvopastures have great potential for improving economic, environmental, and animal welfare outcomes, but their appropriate use will require long-term commitment and a willingness to manage complexity. This is a different paradigm for many who have been trained that livestock and forests cannot be managed together. However, a growing cohort of producers and resource professionals see the potential benefits of these systems. Those producers who are well-positioned to intentionally and intensively manage their unique forest, forage, and livestock resources will be best able to implement silvopastures, but given the complexity and skill sets required, it is highly advisable that producers develop a team of professionals to implement these systems.