Over the past few years you have probably heard quite a bit of talk about non-native invasive plant species (NNIPS). These exotic plants cost the United States billions of dollars annually! So what does this mean to your wildlife management? The fact is there are some exotic species that have the ability to turn your whole property into a monoculture of themselves, and then there are those that have been there longer than you and have never seemed to be a problem. There are wildlife species that can tolerate certain changes brought on by some invasives, and some that can’t. And then there are endless other factors like soils, land use practices, and light availability that could drastically affect how NNIPS will affect your land and your management. This article will address some of the important issues dealing with NNIPS and wildlife habitat management.
It helps sometimes to remember the following concept…unless you’re managing for exotic wildlife, using exotic species to build the bulk of your habitat probably is not the best answer. The wildlife species we have here in the Southeast are used to feeding, hiding, and living in the native trees, shrubs, and herbaceous vegetation found here. Many wildlife species (from butterflies to bobwhites to whitetail bucks) actively seek specific kinds of native trees or plants, to which they have adapted, throughout the year for different reasons. If these native habitat components have been displaced by NNIPS, then the wildlife often moves on as well. Some animals you manage for may be tougher than others when it comes to trading beggarweed for kudzu, but you must know that some critters just won’t stand for it.
What makes a plant dangerous to your wildlife habitat?
First of all, let us examine the ecology and nature of invasive plants. Not all invasives, of course, are non-native. Take our common saw-tooth blackberry (Rubus argutus) for example, a native shrub in the South. After you harvest a stand of timber, this species can respond vigorously via seed and sprouting as a result of the removal of the canopy and the increased light. This is the blackberry’s strategy for getting ahead of the game. But this response is considered a part of the natural system of the South and because saw-tooth blackberry is native and most other natives have co-adapted with it, they can deal with it through natural cycles, succession, and disturbance. At some point the blackberry is limited and does not completely dominate the stand. In turn, not all non-natives are invasive. It’s hard to work to grow a good stand of silver queen roasting ears, and cultivated varieties of corn don’t usually make a crop from year to year unless you invest some effort. But the true NNIPS, the real bad guys, are smart and usually tough to get rid of. Species like cogongrass have an arsenal of strategies for choking out your wildlife habitat.
Cogongrass (Imperata cylindrica), originally from Southeast Asia, is a super-weed quickly spreading northward from the southeastern coastal plain, and is definitely one NNIPS all wildlife managers should invest the time to learn about and defend against. One of its threats, a strategy common to many “stand-replacing” NNIPS, is the aggressive growth attack. It grows and spreads very quickly because it outcompetes virtually all of the native species we have. It physically bullies its way through stands of bluestem, wiregrass, or whatever else gets in its way. It builds an amazing mass of starchy rhizomes that it uses for the following year’s energy source. These rhizomes have sharp and hardened tips and can penetrate pine roots. On top of the ground it generates a dense (and also very flammable) mat of thatch that can bog down a cat dozer. If ignited, this thatch burns so unnaturally hot it often kills the overstory trees that are present in the stand. With no surviving saplings or canopy trees, and without the ability to regenerate from seed (the cogongrass thatch quickly grows back after a fire, choking out native tree seedlings), native woodlands can eventually turn into biological deserts.
The foliage of cogongrass is coarse and full of silicates; unpalatable to wildlife. And although I found no current research looking at cogongrass in regards to insect production, I have generally observed lower insect numbers in established cogon stands. A reduction in insect biomass has major implications in regards to brooding and foraging habitat for species like quail, wild turkeys, and many non-game bird species. Even if there were lots of bugs in a patch of cogongrass, its structure is generally too dense for most ground dwelling birds to negotiate or to use for winter seed-scratching habitat.
Any type of soil disturbance, including disking, grading, or that associated with timber harvest generally increases the likelihood of NNIPS introduction and/or spread. This is typically the case with cogongrass. Cogongrass rhizomes, which can readily sprout into new infestations, are easily broken off and moved around by these types of activities. Cogongrass also makes a lot of small, fluffy seeds that can be dispersed by the wind or hitch a ride on a tractor, bush-hog, or automobile. In a nutshell, cogongrass has a very good strategy of making it hard on your native wildlife habitat. Many other NNIPS have their own suite of weapons that will be arriving in your area soon, if you don’t have them already. So having a plan to deal with them would be a wise move.
Prioritization for NNIPS management
Some species of NNIPS (like cogongrass) will probably warrant more attention than others. And it is generally a good idea to take care of small isolated infestations of a particular species located in or around an area planned for disturbance, (timber sale, agriculture operation, etc.), before diving into large and widespread (saturated) infestations. If you do have a significant amount of NNIPS on your land already, treatment prioritization will be very important. Depending on your location and existing infestations, combating your weeds can be a fairly significant effort and expense. However, these costs are usually increased by waiting longer. Your prioritization will likely be influenced by the wildlife species you manage. You are probably already pretty familiar with the specific habitat requirements of your target wildlife species. Once you know your wildlife’s needs, (or you want to manage for all potential wildlife species), the next step is to become familiar with NNIPS. You can run a web-search of the invasives in your local area, contact your local chapter of the Southeast Exotic Pest Plant Council (www.se-eppc.org/), or ask your County Extension Agent to provide information about local NNIPS issues. Once you see where your issues are, (where there is overlap in what habitats are affected by the NNIPS you have or are at risk of having, and the habitats you want to protect), you can draw some lines in the sand. An inventory map of what NNIPS you already have will also be a good tool to start with. It doesn’t have to be a perfect inventory, just something to use to help you determine what needs treating and what got treated. Herbicide will most likely be your first line of defense. Research of the major types of herbicides may also be needed depending on your level of expertise. A summary of herbicide recommendations can be found in Table 1.
Table 1. Common NNIPS found in the southeast, the habitats they can affect, and some common herbicide treatment recommendations.
* Herbicide recommendations derived, in part, from USDA Forest Service Technical Report SRS-62, Nonnative Invasive Plants of Southern Forests by James H. Miller, 2007. Caution: Always consult the herbicide product label for safe and legal application rates as some herbicides can affect non-target vegetation.
If white-tail deer are your major management concern, you may be able to tolerate some exotic species without seeing any declines. In fact, deer actually like to eat many exotic plant species, but there are thresholds with every species as to how much is too much over their home range. And unfortunately that’s where the problem lies with NNIPS; they don’t usually know when to quit spreading and the costs often outweigh the benefits. Chinese privet (Ligustrum sinense) is quite common across the Southeast and deer will utilize it heavily for browsing in winter months, especially when acorn mast is low (Stromayer et al. 1998), as well as for cover. Privet foliage averages around 12% crude protein and has been suggested to be an effective management component for deer. Japanese honeysuckle (Lonicera japonica) and kudzu (Pueraria Montana) are also browsed by deer and both can average around 16%, although kudzu is only available in the growing season. Deer may even sporadically graze exotic sod-forming pasture grasses like tall fescue (Lolium arundinaceum), again with a similar protein content, depending on the season. But again, these NNIPS are sometimes stand-replacing, and can occupy the space of native plant species that build the habitat of other wildlife species. Whitetail deer do have limits as to how much they can adapt to, and a property dominated by NNIPS is generally not a preferred situation.
Many other species are generally much less tolerant of NNIPS infestations. Bobwhite quail, for example, prefer native herbaceous understories occurring in an open forest structure (lots of available sunlight). Most areas will have a wide variety of native species already growing on the site or in the seedbank. An abundance of native grasses like bluestems (Andropogon spp. and Scizachyrium sp.), panic grasses (Panicum sp.), native paspalums (Paspalum spp.), lovegrass (Eragrostis spp.), threawns (Aristida spp.), and Indian grass (Sorghastrum spp.) creates excellent nesting and foraging cover for quail. The conditions provided by these native bunchgrasses are completely different than those produced by exotic pasture grasses. Native legume and forb species (including beggarweeds (Desmodium spp.), native lespedezas (Lespedeza spp.), tephrosias (Tephrosia spp.), crotons (Croton spp.), and others generate lots of high protein seeds that are utilized by quail. Ideal brood-rearing habitat (commonly achieved by fall and winter disking) typically includes lush native pioneers like partridge pea (Chamaecrista spp.) and ragweeds (Ambrosia spp.). This diverse native understory system, often maintained by periodic prescribed fire and/or mechanical disturbance, is also a prime target for NNIPS.
Many NNIPS can spread quickly in open uplands due to the ample sunlight and frequent fire or other disturbance. Depending on soils and other factors even species like bicolor lespedeza have the potential to outcompete and shade out natives. While bicolor makes lots of good seed, quality nesting and brood-rearing habitats, (typically the more limited requirements), can sometimes be displaced by it. Many quail managers have found that they can not effectively control bicolor on clay soils in open, burned pine stands. And once it is established, it is extremely difficult and often expensive to exterminate due to several season’s worth of seed in the seedbank. However in certain situations, for example where it is adjacent to dense (shady) timber stands or on some very sandy soils, bicolor may be physiologically limited and can persist without causing too much of a problem.
Cogongrass, kudzu, Japanese climbing fern (Lygopodium japonicum), sericia (Lespedeza cuneata), tallow tree (Triadica sebifera), privets (Ligustrum spp.), invasive roses (Rosa spp.), and many other NNIPS are all bad news for quail management, because of their ability to outcompete and displace the native understory. Although quail may occasionally use some of the coarser NNIPS (like privet or rose thickets) for escape cover, the NNIPS would be better traded for native structure like sumac (Rhus spp.) or bramble (Rubus spp.) patches. These natives won’t overrun your brooding and nesting habitat.
Each species of wildlife with its own unique habitat requirements will be affected a bit differently by each NNIPS, depending on the severity of the infestation. Again generalists, like wild turkey and white-tail deer, are usually more apt to tolerate the changes, and habitat specialists, like quail and Bachman’s sparrows, for example, may not be able to cope as well with a large percent of their preferred habitat being affected. Quail may be able to tolerate a few of the less invasive exotics, like Brazilian vervain (Verbena brasiliensis) which does not generally dominate the understory, but as a general rule the fewer NNIPS the better for bobwhites.
Non-native wildlife plantings
So what about wildlife food plots? Don’t we usually plant them with non-native plant species? That is a true statement but hopefully we are planting them with non-natives that are not invasive. While some invasive plant experts recommend using only native species and planting absolutely no exotics in forest settings, there are many non-native species that are valuable as forage and harvest attractants that probably have their place in good wildlife management programs. Some common wildlife food plot species like wheat, oats, white clover, corn, browntop millet, milo, sunflowers, and cowpeas don’t usually pose a problem for most locations. However, there are tons of species labeled and recommended for food plots that you should thoroughly examine before planting. Some wildlife plantings recommended by various entities, including the seed companies and even conservation-type agencies with good intentions, can often be time bombs, depending on what setting you stick them in. In many cases on both public and private lands, what we once thought was “the greatest idea ever for wildlife food” we are now struggling to get rid of by investing significant time and money in herbicide applications. Autumn, Russian, and thorny olives (Elaeagnus spp.) are also sometimes recommended for wildlife, but can become problems in the long term, largely due to dispersal of the seeds by birds. Even some of the common food plot grass species like perennial rye (Lolium perenne) and orchard grass (Dactylis glomerata) have persistent, invasive tendencies, and some managers have drawn the line and are opting for less persistent species for their deer and turkey plots. Quail and other small seed-scratching birds are especially sensitive to grasses and other NNIPS that form dense barriers of foliage or litter because they either render edible seeds unobtainable or shade out the native seed-producing plants.
NNIPS Treatment
Although there are several means of control for various NNIPS, usually the most effective, and often the most economical, is using a chemical herbicide program. Simply mowing, cutting, or burning may be somewhat effective on some of the wimpier NNIPS, but the superweeds are probably going to require repeated herbicide application for their control. As we discussed earlier, NNIPS like cogongrass and kudzu have large rhizome reserves that are hard to reach, even with herbicides. The rhizome tissue and carbohydrate that remains after treatment sprouts right back the following spring. Others like privet, tallow tree, Japanese stilt grass (Microstegium vimineum), and bicolor produce mind-boggling numbers of seed that can be tough to deal with. That is why monitoring and re-treatment is essential in an effective NNIPS control program.
Following the eradication of an infestation, native pioneer species will usually quickly re-colonize the treated spot. However if the area is large or if there is significant erosion potential, native or desirable non-invasive vegetation can be planted for stabilization until native species can return.
Summary
On many properties or farms it will be near impossible to eliminate all NNIPS. But by prioritizing the habitats in greatest need of protection, being familiar with NNIPS and treatment options, and having a consistent control plan, one can successfully manage wildlife habitat amidst the hordes of non-native invaders out there. By responsibly managing exotic wildlife plantings and working with neighboring landowners towards a common goal, the chances of long term NNIPS control are greatly increased. In addition to protecting and maintaining quality native wildlife habitats, a NNIPS-free forest and/or farm is healthier, more aesthetically pleasing, and worth more money when it comes to selling or leasing for hunting or farming purposes.
References
Stromayer K. A. K., Warren R. J., Johnson N A. S., Hale P. E., Rogers C. L., and Tucker C. L., 1998. Chinese privet and the feeding ecology of white-tailed deer: The role of an exotic plant. JWM, Vol. 62.
Miller J. H., 2007. Nonnative Invasive Plants of Southeastern Forests. Forest Service Gen. Tech. Report SRS-62.
Southeast Exotic Pest Plant Council website, 2008. www.se-eppc.org/