Short-term impacts of logging on understorey vegetation in a jarrah forest

Abstract

Summary In 1985, new silvicultural treatments were implemented in jarrah (Eucalyptus marginata) forests available for wood production. As part of a scientific investigation into the ecological impacts of two of these treatments, gap cutting and shelterwood cutting, a survey was conducted 4 years after logging to examine the effects of these treatments on understorey vegetation species richness and abundance. Sampling scale was found to be an important factor affecting the results and subsequent interpretation of impacts. At the coupe scale, native plant species richness in unlogged coupe buffers was similar to that in adjacent logged patches. However, the mean number of species per 1 m2 was 20%-30% higher in the unlogged buffers than the logged patches. At all sampling scales, the abundance (number of individual plants) of native plants was 20%-35% higher in the buffers, but the abundance of introduced (weed) species was significantly higher in the logged patches. The abundance of weeds, which are mostly annual grasses and short-lived herbs, is likely to diminish with time. The time to recovery of native species abundance and the ecological significance of this is uncertain. Given the reported low seedling regeneration rate and limited dispersal capacity of many woody shrubs and perennial herbs, they are unlikely to return to pre-logging levels in the medium term. We attribute the reduction in the abundance of native plants mainly to mechanical soil disturbance, which ranged from 60% to 80% of the area of logged coupes, physical damage to the vegetation associated with logging and to intense heating of the topsoil during the post-logging silvicultural burn. Recommendations are made for reducing the negative impacts of logging operations on the understorey.