Comparison of biomass removal, nutrient manipulation and native seed addition to restore the ground layer of a degraded grassy woodland

Abstract

This study reports on a trial of methods to overcome barriers to restoration of degraded Cumberland Plain woodland. Soil scalping was compared with fire or slashing to remove existing canopy. Fire and slashing were combined with soil carbon addition at two levels, to reduce soil nitrate. Native seed was added to overcome a lack of native propagules. Treatments, applied to 2 × 2 m plots, consisted of a control; scalped; fire and slash treatments without carbon addition; fire and slash treatments at the low and the high carbon addition levels; and a further fire and a slash treatment at the low carbon level with no native seed added, to give 10 treatments in total. Scalping eliminated the existing canopy and reduced weed seed and bud banks allowing native species (and some colonising exotics) to establish by 33 months. Rapid re-growth in the fire treatment resulted in plant canopy abundance returning to control levels by 12 months, and native species richness on burnt plots remained similar to the control. Canopy abundance in the slash treatment remained lower than in the controls for 20 months, and native species richness increased by then. Carbon addition reduced canopy re-growth in both fire and slash treatments: in the fire-low carbon plots with added native seed, native species richness was double that of the controls by 20 months. This increase did not occur on slash-low carbon plots. The highest level of carbon addition had negative effects on plant growth and survival, resulting in the lowest native species richness. The non-scalping treatments had little effect on exotic species richness in the absence of carbon or small negative effects if combined with carbon.