Vegetation recovery of rehabilitated pasture at three coal mine sites following fire disturbance

Abstract

Sustainable long-term use of land rehabilitated following mining is required to be resilient to fire and other disturbances. We analysed the vegetation responses to three fires in grassland pasture and open woodland on rehabilitated open-cut coal mine sites in Queensland, Australia. Two fires in central Queensland were controlled burns to manage fuel loads and test the vegetation and landform response, while the third fire, in southeastern Queensland, was an unintended wildfire. We monitored several ecological variables at the study sites for up to five years following the fires and found that vegetation cover, biomass and species richness recovered to pre-fire or unburnt control values within two years. However, one study site experienced lower than average rainfall during the three to five-year post-fire period, resulting in a significant reduction in vegetation cover of between 14 and 31 %, and biomass between 45 and 57 % compared to pre-fire values. Tree and shrub densities changed significantly at two of the sites, reflected in a 635 % increase in stem density of Acacia stenophylla (A.Cunn. ex Benth.) and 82 % mortality of Atriplex nummularia Lindl. subsp. nummularia individuals <2 m in height and 100 % mortality in the 2-5 m height class. The results suggest that rehabilitated pasture systems in central and southern Queensland are resilient to fire in the short-term but are vulnerable to long-term shifts in climate, particularly if a fire precedes a long period of drought. Further resilience work is needed to i) compare rehabilitation recovery with unmined vegetation communities to determine residual risk of future fire impacts, ii) account for seasonality in resilience assessments and iii) understand recovery traits of seed mix combinations sourced from disparate regions.