Revegetation in agricultural areas: development of structural complexity and floristic diversity

Abstract

Revegetation plantings have been established to ameliorate the negative effects of clearing remnant vegetation and to provide new habitat for fauna. We assessed the vegetation development of revegetation established on agricultural land in Gippsland, southeastern Australia. We compared (1) woodlot plantings (overstory eucalypts only) and (2) ecological plantings (many species of local trees, shrubs, and understory) with remnants and paddocks for development of vegetation structural complexity and colonizing plant species. We also assessed structural complexity and plant species composition in response to several site parameters. Structural complexity increased with age of planting, toward that of remnants, even when very few species were planted at establishment. Richness of all plants and native plants, however, did not increase with age. Native ground cover plants were not included at establishment in either planting type, and their richness also did not increase with age of planting. This indicated that colonization did not occur through time, which does not support the "foster ecosystem hypothesis." Weed species richness was unrelated to native plant richness, which does not support the "diversity-resistance hypothesis." Weed cover increased with age of planting in woodlot plantings but decreased with age in ecological plantings. Richness of all plants and native plants in plantings did not increase with planting size or with the presence of old remnant trees and was greater in gullies and where vegetation cover in the landscape was greater. Structural complexity was unaffected by planting size but was positively correlated with floristic richness. Ecological plantings had higher condition scores, greater shrub cover, more plant life-forms and fewer weeds than woodlot plantings indicating a possible greater benefit as habitat for wildlife. We conclude that ecological plantings can achieve similar overall structural complexity as remnant vegetation within 30-40 years but will not gain a native ground layer and will not necessarily contain some important structural features by this age. Ecological plantings may provide habitat for the conservation of fauna (through the development of structural complexity), but they may not provide for the conservation of non-planted flora (given the absence of re-colonizing smaller life-forms).