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Thinning timber to create silvopasture

John Fike Published on 26 September 2014
Thinning stands of trees

Silvopasture management integrates trees with forage-livestock production systems and has great potential to boost farm resource use and income.

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 also can 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.

Certainly, the quickest way to create silvopastures is to thin an existing tree stand and then establish forages. Producers often prefer this way because it shortens the investment time, but several issues should be regarded before taking this approach.

Build a team and plan, plan, plan
Given that few producers (or professional consultants) have experience across both forage systems and forestry, perhaps the first recommendation for getting started should be to build a team.

Extension agents, foresters or arborists, and technical service providers (from NRCS or soil and water districts) working together can greatly assist in considering goals, site suitability, implementation strategies and best management over short-term and long-term horizons.

Silvopasture development involves significant investment, requires taking the long view and is not changed rapidly once set in place, so careful preparation is essential.

Fire can be an effective tool

Site suitability
On many farms, the backwoods are the backwoods because they have some of the worst ground. 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 may provide a functional way to advance land management through timber stand improvements, invasive species removal and soil re-vegetation. 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, timber quality and value all play a role in the current and future returns to the system.

These factors also affect the suitability of managing with forages and livestock. Along with these considerations, thinning decisions should account for farm layout and infrastructural needs, which don’t always match the preferred harvest plan.

Knowing how much timber to remove (and when) can also be perplexing. Removing 50 percent of the basal area of the existing tree stand is a common rule of thumb and is a reasonable balance point for getting adequate light to the forages without compromising the tree stand.

However, this may be insufficient on sites filled with healthy but small-diameter trees, and it may be too intense if the trees left post-harvest are tall, thin and top-heavy, and would be susceptible to damage from high winds or ice.

In some cases, multiple thinnings over time may be best for the tree stand, but this approach must be balanced against greater costs, slower conversion and the potential for more damage from harvest operations.

Thin tree stands

Some economic considerations
Having a forester evaluate timber and provide good thinning decisions is important to get the most out of timber stands over the short and long terms. Set thinning specifications and seek bids for the job to get the greatest economic return.

Bid ranges of 100 percent are typical, and fourfold bid differences are not unheard of. Having a logger who accepts the vision of leaving some trees of greater genetic merit also is important, and combining harvests across good and poor stands and small tracts increases the likelihood of acceptable bids.

Stumps, timber harvest, residue management and forage establishment
Residual tree stumps can be problematic to work around. Setting stump height limits and discounts for those trees not meeting this standard can be useful. If future management will not include large machinery, strict limits on stumps or harvest residues may not be necessary.

With sparse tree stands, removing residue may not be justifiable or necessary. However, residue management typically will be needed post-harvest. This may be as simple as pushing the remaining wood into piles and burning or “removing” these materials by mulching.

Mulching also is a good way to remove standing small-diameter junk wood without causing excessive soil disturbance, although it can affect establishment. 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. High seeding rates may 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 often is the only suitable method of seeding thinned tree stands. High levels of carbon-rich, low-nitrogen residues also “tie up” 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 limited for use over large scales.

Producers also should consider time of seeding to minimize leaf-fall effects on young seedlings.

goats can remove understory vegatation and stump regrowth

Soil fertility
Many forest soils have very low pH and poor fertility. Achieving fertility levels suitable for good forage production may be difficult logistically, economically or both. When fertility 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.

Forage species and grazing management
Several 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 grasses (e.g., bahia 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 generally are less tolerant of shaded environments than grasses, but there is a broad range in adaptation among grass and legume species and varieties. However, there has been little effort to compare and select for shade tolerance in forages.

Whatever the forage, rotational grazing management is highly advisable for silvopastures. The greater the amount of shading, the longer the rest period needed for forage plants to recover. Similarly, less intense defoliation than is typical for open pastures may help maintain stands growing in deeper shade.

Silvopastures have great potential, but they require long-term commitment and a willingness to manage complexity. This is a different paradigm for many producers, but a growing audience sees the benefits and will begin to adopt these system as they learn more of the “hows” of implementation.  FG

PHOTO 1: Thinning stands can be the quickest way to functional silvopastures, but many questions need consideration before jumping in.

PHOTO 2: Fire can be an effective tool for residue removal.

PHOTO 3: Where tree stands are thin, it may be advisable to let downed trees decompose in place.

PHOTO 4: Goats can remove understory vegetation and stump sprout regrowth. Photos by Chris Fields-Johnson, Bartlett Tree Experts, Greg Frey and Dusty Walters.

John Fike
  • John Fike
  • Forage – Livestock and Biofuels Research Crop
  • Virginia Tech