Academic journal article The American Midland Naturalist

Effects of Method of English Ivy Removal and Seed Addition on Regeneration of Vegetation in a Southeastern Piedmont Forest

Academic journal article The American Midland Naturalist

Effects of Method of English Ivy Removal and Seed Addition on Regeneration of Vegetation in a Southeastern Piedmont Forest

Article excerpt

Abstract.-

Invasive plants can have substantial negative impacts on native flora and fauna. As a result, ecological restoration often involves removal of invasive species. We examined the effects of the removal of Hedera helix (English ivy) on regeneration of native vegetation in the Piedmont of Georgia. Ivy was removed by hand or by herbicide from five 5 m × 5 m plots for each treatment and half of each plot was seeded with native seeds. We then counted the number of seedlings present in each plot bimonthly over a 5-mo period. Ivy removal by pulling resulted in the greatest density and diversity of seedlings. Furthermore, these plots exhibited increased seedling density and diversity due to seed addition. Spraying was effective in removal of the ivy but significantly lowered seedling density and diversity and hindered any seed addition efforts. Control plots in which ivy was not removed had no seedlings germinate. Our results suggest that the method of exotic plant removal and the addition of native seed can have profound effects on the regeneration of native vegetation and should be a major consideration for future exotic plant removal projects.

INTRODUCTION

Many native plant communities have been impacted negatively by invasive species infestations (Reichard and White, 2001). As a result, invasive species are now considered the second largest threat facing imperiled species after habitat loss (Wilcove et al., 1998). Introduced species cause this negative change in the community structure by multiple processes (Vitousek et al., 1997; Westbrooks, 1998; Levine et al., 2003; Didham et al., 2005). For example, introduced species are better dispersers than many native species and, therefore, can better exploit disturbed habitats. In addition, introduced species often can outcompete native species directly. In some instances, they can chemically or physically modify habitats, which decrease the suitability of the habitat for native species.

These differing processes of invasive dominance can lead to unexpected outcomes upon removal of the invasive species. For example, after removal of an exotic grass in garry oak (Quercus garryana) meadows, native vegetation did not recover (MacDougall and Turkington, 2005). The researchers determined that the invasive grass had affected seed bank and seed recruitment and diat active seeding had to occur before native vegetation recovered. Therefore, the prominent mechanisms by which exotic species impact native plant communities need to be determined, because the success of invasive species removal and native species restoration can be affected by these differing mechanisms.

In forests in the southeastern United States, English ivy Hedera helix L. is an exotic species that is naturalizing rapidly. Once established, ivy forms a dense ground cover that prevents the emergence of almost all herbs and dramatically reduces light levels (Thomas, 1980). This reduction in light levels can weaken trees and cause collapse either by outright death or by increased susceptibility to damage by ice storms and winds (Penfound, 1966; Sicama et al., 1976; Thomas, 1980; Harmer et al., 2001).

The substantial negative impacts of English ivy on native vegetation require that methods of ivy removal and the differing methods' subsequent effects on forest restoration be explored. Derr (1993) has shown that a 25% glyphosphate treatment coupled with cutting of the ivy's leaves to facilitate herbicide absorption will result in an almost 100% removal of ivy from the affected area. Neal and Skroch (1985) also have shown that timing of herbicide application is important, with herbicide application in March being most effective. Although herbicides can be effective in removing ivy, herbicide use introduces a potential environmental contaminant and is nondiscriminatory toward native foliage. However, the use of herbicides will leave root structure intact, which can prevent soil erosion and nutrient leaching, but may continue to smother seedlings even though the plant itself is dead. …

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