Vegetation that is diverse in species composition and structure will generally support a greater amount of wildlife. In the lifetime of a forest, the earliest years after planting are characterized by relatively high vegetation diversity. With little to no tree cover, there is greater light availability to support many plant species. This extra light also means the soil is also more heated, which accelerates decomposition rates. Faster decomposition has a natural fertilization effect, releasing nutrients that further enhance plant species diversity and growth. However, this abundance in vegetation also hampers the success of replanting forests. Tree seedling growth and survival is significantly reduced when other vegetation is fast-growing and plentiful because it takes light, water and nutrients away from the seedlings. Essentially, wildlife looks at a site full of vegetation and sees food and cover, while a tree seedling “sees” a field of “weeds.” This problem is most pronounced in the southeastern U.S. for southern pine species because pines are natural early colonizers of disturbed, cleared areas. Their relatively fast height growth is their tactic for getting above plant competitors, but often a small percentage of seedlings will survive to get above the weeds if left on their own to “duke it out.”
To help pine seedlings get established, forest managers often do some sort of competition control. The most common pre-planting competition control techniques are applying herbicides and/or controlled (prescribed) burning. Although suppressing vegetation would seem to be at cross purposes with supporting wildlife, there are numerous ways in which competition control and wildlife habitat enrichment can be balanced. The objective of this article is to provide information on how this balance can be achieved.
Herbicides are one of several management options in the forester’s “toolkit” for establishing forests. Combining herbicides in certain ways with other management practices helps with sustaining vegetation and wildlife diversity. Planting a good number and configuration of seedlings will provide ample trees for future harvests while keeping light available for a longer time for the benefit of vegetation and wildlife. For example, long-term research at the LSU AgCenter Hill Farm Research Station and other universities has shown the best number of loblolly pine seedlings to plant is between 400 to 600 trees per acre. Planting closer to 400 trees per acre will help with keeping light available for longer. Planting seedlings in what are termed rectangular spacings can further improve light availability. For example, planting seedlings on a square spacing of 10 feet by 10 feet results in 435 seedlings per acre. Planting seedlings in a rectangular spacing of 6 feet within each row and 17 feet between rows results in 427 seedlings per acre. This amount is nearly the same as with the 10 feet by 10 feet spacing, but with its wider rows it will be longer until tree crowns grow together and shade out the understory. Prescribed burning is another powerful pre-planting option that can be combined with herbicides to enhance vegetation diversity. Fire improves plant richness by enhancing soil nutrient availability and increasing soil pH. Research has shown that bird diversity is especially enriched by prescribed burning after herbicide application.
Herbicide applications can be conducted in ways to balance tree seedling survival with vegetation diversity. Tree seedling survival and growth is maximized by broadcast-applying a mixture of herbicides that suppress woody, grass and herbaceous vegetation for the first year after planting. This management approach is helpful when timber production is the primary objective, although research has shown that even the most aggressive herbicide treatments have relatively high vegetation and wildlife diversity three to five years after application. The most commonly used herbicides for southern pine management are imazapyr (Arsenal, Chopper), sulfometuron methyl (Oust), metsulfuron methyl (Escort), triclopyr (Garlon), and glyphosate (Roundup). The trade names provided here are the ones with which the herbicides were originally developed; there are also generic equivalents for each of them sold with different names. Each of these herbicides controls different species of vegetation, so they are often applied in mixtures to control a higher number of species with one application. However, these herbicides and others can be applied in ways that leave groups of vegetation species alone so wildlife can benefit while seedlings still gain some competition control.
For more information on this topic, contact Michael Blazier at firstname.lastname@example.org.
— Michael Blazier is a professor at the LSU AgCenter Hill Farm Research Station and the School of Renewable Natural Resources. He is a forest management specialist.