In bioenergy, a common concern related to the scale-up of some energy crops is invasiveness. The introduction of many invasive plants has occurred intentionally, as with ornamental plantings, and accidentally as a by-product of commerce. Herein lies the concern with bioenergy crops. No one wants to unintentionally introduce the next Kudzu! To evaluate potential energy crops and gauge their invasiveness, we first have to understand what invasive plants really are. What makes them invasive? How do we know a crop may be invasive? To find out, let’s start with some basic definitions to make sure we are all on the same page.
Vegetation historically found in a local area is termed native vegetation. These plants have traditionally been found in the area and are well-suited to maintain themselves in their environs. Exotic plants are those plants found in a particular area, but originate from another continent or country. These plants can also be referred to as non-native. However, non-native plants are not always exotic. Non-native plants maybe also be native elsewhere in the same country, but not found in the local area. For example, redwoods are native to California and would be non-native in Tennessee, but not exotic. Invasive plants are plants, native, non-native, or exotic, that can cause significant ecological or economic damage. Invasive plants can out-compete more ecologically and economically valuable plants. These plants are typically characterized by a rampant rate of spread. This rate of dispersal is due to both human activity and vegetative characteristics. Humans play a large role in the dispersal of plants by moving plant materials to and from locations as well as by causing significant disturbances to native plant communities that provide opportunities for the establishment of exotic and/or non-native invasives. The seeding and sprouting characteristics of the plants and their roots also significantly contribute to the rate of dispersal. Though a negative term, “invasive” plants can also be native plants that we usually do not consider to be a problem. Examples this type of native plant are sumac (Rhus spp.) and poison ivy (Toxicodenron radicans). Native or not, invasive plants exhibit several characteristics that enable them to become invasive problem species, particularly the methods by which they reproduce.
One reproductive tool of many invasive plants is to produce thousands of light, wind-blown seeds per plant that can rapidly disseminate to other areas. Many of these invasive plant seeds have very hard seed coatings. This coating protects the seed and allows it to remain viable for several years after being dropped by the parent plant. Seeds of invasive plants can lay dormant in the soil for years, waiting for the appropriate weather and site conditions to occur. Conditions that facilitate seed sprouting can include several wet growing seasons, site disturbance that increases light availability and/or clears the soil surface of other vegetation, or droughts that affect competitors. Scarification of the seed coat, by animal or other means, can also stimulate sprouting. Scarification occurs when the seed passes through an animal’s digestive track. The fruits and seeds produced by invasive plants are usually very attractive to wildlife as a food source and subsequent seed dispersal. Birds, in particular, play a large role in disseminating seeds over broad areas. Another reproductive characteristic is the ability of invasive plants to sprout from roots and root nodes along the stems. If the aboveground vegetation of an invasive plant is killed, the roots can rapidly send up a replacement sprout. Some plants reproduce by root nodes located along the aboveground stem. When one of the root nodes comes into contact with the soil surface, a new root system begins to develop and eventually forms another plant.
In the next part of this series, we’ll focus on the evaluation of energy crops for invasiveness and look at technological developments that may help us address potential invasives.
By Sam Jackson, VP of Development
