Patterns of Invasion: Trends in Abundance of Understory Vegetation, Seed Rain, and Seed Bank from Forest Edge to Interior

Abstract

Non-native species are often abundant in the vegetation of forest edges, decreasing in abundance with distance into the forest interior. Regenerative strategies such as the seed rain and seed bank were expected to exhibit a similar pattern of decrease from the edge to the interior; however, this has been rarely investigated. Trends in abundance of the understory vegetation, seed rain, and seed bank of both native and non-native plant species from forest edge to interior at three different natural areas bordered respectively by a crop, a hay field, and a forest access road were quantified. Three 90 m transects were established perpendicularly across each of the three edge types into the forest interior. Twelve 3.14 m2 circular plots 5 m apart for the first 20 m and 10 m apart thereafter were established along each transect. We compared the abundance of all vascular plant species in the vegetation, seed rain, and the soil seed bank in these plots. Species richness of the vegetation, the seed rain, and the seed bank (native and non-native species combined) decreased from the forest edge into the interior. Sixteen non-native species were observed and were limited to 30 m from the forest edge. Out of these 16 non-native species, > 50% were found only in the seed bank. We observed different trends in abundance of native and non-native vegetation, seed rain, and seed bank for some species. Our study suggests that removing aboveground biomass of non-native species may not be the only thing to consider in non-native species management because of the high frequency of additional non-native species in the seed bank that are absent from the existing vegetation. In order to minimize non-native species, managers should eradicate seedlings of non-native species along forest edges before they mature and produce seed.