Regrowth vegetation in production landscapes: comparisons between remnant and regrowth Brigalow (Acacia harpophylla) communities, Southern Queensland

Endangered Brigalow (Acacia harpophylla F. Muell. ex Benth.) dominated ecosystems have been extensively cleared and modified for agricultural production throughout the Southern Brigalow Belt Bioregion of southern Queensland, Australia. Intensification of the agriculture in the region has resulted in significant fragmentation and disturbance of natural vegetation remnants. Rehabilitating previously cleared vegetation (regrowth) is an important conservation alternative where there is inadequate cover of intact remnants, that aims to ensure the persistence of Brigalow communities throughout highly modified landscapes. While legislation is now in place to restrict clearing of remnant and Brigalow regrowth in southern Queensland, little is known of the functioning and dynamics of regrowth communities in comparison to remnant vegetation. This research investigates patterns in floristic composition, stand structure and microenvironment of Brigalow remnants and a number of regrowth communities differing in time since clearing. Thirty-eight sites in the Darling Downs region, southern Queensland, were sampled encompassing Brigalow remnant (two treatments: 'Remnant‘ (sites with an absence of clearing but continue to experience small disturbances such as grazing) and 'Reserve‘ (sites with an absence of disturbance within state and national reserves)) and different aged Brigalow regrowth (40 years). Floristic composition and projected cover of strata were recorded in a 500m2 quadrat at each site. Patch and surrounding landscape context (spatial) environmental data were also determined for each site. Soil chemical data (including soil, pH, organic content, cation exchange capacity and phosphorus and nitrogen concentrations) were determined from bulked soil samples. Landscape spatial data was derived from remotely sensed imagery. Un-weighted paired group arithmetic averaging (UPGMA), non-metric multidimensional scaling (nMDS) ordination, analysis of similarity (ANOSIM) and analysis of variance (ANOVA) were used to identify patterns in composition, functional group richness and stand structure between remnant and regrowth sites. Canonical Correspondence Analysis (CCA), Kruskall Wallis correlations and linear step-wise regression were used to identify potential environmental drivers of vegetation responses (Appendix I). Multivariate analyses (UPGMA and nMDS) showed general gradients from recent regrowth through older stages of regrowth to remnant and reserve sites for both floristic composition and stand structure data. There were no differences between remnant and old regrowth (>40 years) in terms of stand structure (ANOSIM, p