Changes in the structure and species dominance in vegetation over 60 years in an urban bushland remnant

Abstract

Kings Park bushland is an urban remnant of predominantly mixed Eucalyptus-Allocasuarina--Banksia mediterranean climate-type woodland in southwestern Australia. This paper presents the results of one of the longest quantitative comparisons on multispecies temporal differences in the Southern Hemisphere. In 1939, the locations of individuals of 13 dominant native tree and shrub species were mapped in 126 transects in a 60 ha portion of the bushland. Observations of the same transects were undertaken in 1999, and the temporal differences in the presence of the same 13 species compared both with univariate and multivariate analyses. There have been substantial changes in vegetation structure and species dominance within the plant community in the 60 years period. In the woodland canopy, there has been an increase in Eucalyptus gomphocephala, E. marginata, Corymbia calophylla and Allocasuarina fraseriana and a decline in once dominant Banksia species. In the mid-storey there have been increases in the density of Dryandra sessilis and Acacia saligna. The changes in structure and species dominance may be considered as changes between different community variants that all occur in the vegetation of the Swan Coastal Plain. The main factors that may be responsible for vegetation change are weed invasion, changed fire regime and seed predation of some species. Disturbances beyond the control of managers (such as wildfire) have altered the composition of the vegetation. However, changes in management procedures in the urban reserve, such as weed removal with herbicides and cessation of fuel reduction burning have also been successful in altering the prominence of some native plant species in the Park. The outcomes of this study indicate that in urban remnants of once natural ecosystems the relative dominance of species may change in response to changes in disturbance regime and hence recruitment cues and this may have important consequences in terms of managing and conserving fauna and flora assemblages, including rare species, in reserves.