A forum member recently asked about creating silvopastures for their goats with black locust. In my opinion, black locust is just about the perfect tree for converting open pasture areas into silvopastures. Some notable qualities include:
On the downside, black locust can spread into unwanted areas by seed and suckers, and has thorns on the juvenile wood (new growth) that can puncture tires and skin.
The most significant pest of black locust is the locust borer, which can damage and occasionally kill young trees. Vigorous, fast-growing locust are considered to be much less susceptible to borer damage than those struggling to grow on poor sites, or due to drought or weed competition. Adult borers emerge in late summer and feed on goldenrod pollen before laying eggs on the bark of young locust, so controlling this food source through mowing or spraying may help reduce borer populations and damage.
Black locust has the potential to be a profitable timber crop if well-managed on a decent site. The selection of quality planting stock, good site preparation, and maintenance until trees are well established will enhance the growth, survival and profitability of the plantation. There is considerable genetic variation in black locust as to form and straightness. Care should be taken to select planting stock from “improved” (straight) selections of locust to maximize the yield of usable posts and sawtimber.
After planting approximately 700 trees/acre (about 8’ x 8’ average spacing, in whatever design seems most convenient), thinning should occur about every five years starting at year fifteen. For best results, cull the smaller and poorer quality trees for posts and firewood in each thinning. The plantation can be managed on a short rotation (< 25 years) for posts, or longer rotation for posts, poles, sawtimber - and of course, shade for the livestock. Round posts from locust are currently in high demand and sell for $6 to $12, depending on size and quality. Poles can be worth several times that, and are also in demand for applications like hops plantation trellises, pilings and pole barn construction. Black locust lumber retails for $3 to $6 per board foot. Once a plantation reaches maturity based on the desired mix of products, the remaining best quality trees can be clearcut during the dormant season to stimulate vigorous coppice and sucker regrowth. These second-growth plantations will have a high number of stems per acre and will require thinning at an earlier age to promote the growth of the best individuals.
Suckers and stump sprouts will result from trees that are harvested during intermediate thinnings, but tend to die out after 1 to 2 seasons under a canopy of larger trees (locust is very shade intolerant). Allowing livestock to browse the sprouts only lightly and very occasionally when the leaves are out may help this source of browse persist longer.
Most literature points out the potential toxicity of locust browse from condensed tannins. We have not experienced any issues with our animals eating locust foliage - but graziers should experiment with caution. Susceptibility to tannins is probably a combination of: adaptation; health of the animal's immune system; supplemental forages, minerals and plant compounds (from other grazed and browsed plants) that can help dilute or bind the tannins; stage of maturity of the locust foliage; growing site; type of livestock; etc. Everyone's farm, animals and conditions will be different - so beware!