Weed Management and Invasive Species Control - Project Planning and Management for Ecological Restoration - page 186

restoration project. Nonnative invasive plant species are generally the most aggressive “weeds”
on, or adjacent to, a restoration project site. This is because many of these invasive plant species
evolved in a different region of the world and thus have a competitive advantage because they are
no longer controlled by their natural predators. The term control here means eradicating, sup-
pressing, reducing, or managing invasive species populations, preventing the spread of invasive
species from areas where they are present, and taking steps, such as the restoration of native species
and habitats, to reduce the effects of invasive species and to prevent further invasions (US Federal
Register, February 8, 1999, Executive Order 13112).
We use the terms weeds and invasive species interchangeably. Other terms commonly used for
weeds and invasive species are alien species , exotic species , exotic pest plant species , invasive exotics ,
exotic invasives , noxious weeds , and wildland weeds .
Need for Weed Management
Depending on the type of vegetation or system in which you're working, you may find it acceptable
to allow certain weeds to become established on your site. However, in most cases, it is important
to control the weeds because they can seriously affect the development of your site. One of our
projects had a three-month interruption in plant maintenance following plant installation. This
hiatus was sufficient to allow a lush growth of weeds to establish. Several thousand dollars later, we
were able to clear the site of many weeds and found that all of the native plants were smaller and
less well developed than on parts of the site that had not been subjected to the lush weedy growth.
In this example, weeds clearly retarded the growth rates of the installed plants, and the density
of the weeds directly affected the amount of growth by those desired plants. This effect may have
consequences later if you have planned and budgeted limited resources for maintenance.
Of course, the weed species involved are very important in your maintenance program pro-
tocols. Some weeds are annuals and produce vast quantities of viable seeds, whereas other weed
species may be woody shrubs that take longer to propagate. There are numerous weed species that
do not overpopulate an area and cause negative effects and therefore do not require active control.
We consider these species to be low priority based on their characteristics in relation to disruption
of restoration sites.
The key to any weeding effort is a consistent program routinely executed. It does little to weed
aggressively for a short time and then disappear altogether for a year before re-initiating a weeding
program. Attacking weeds only once with herbicides or hand weeding may actually worsen the
situation (Murphy et al. 2007). If your project relies on professional workers to perform these tasks,
then you should have sufficient funds budgeted to get the site through at least the first growing
season and preferably at least two or three seasons.
Most restoration sites are degraded areas where weeds typically flourish, preventing the estab-
lishment of native plants. Some invasive plants change ecosystem processes, such as hydrology,
soil chemistry, and fire regimes. Many of the weeds that have displaced native groundcovers are
prickly or spiny to the touch, making maintenance in restored sites challenging. Tall weeds can
overtop and shade new plantings, causing reduced plant growth and vigor. Weeds also compete