Decreasing net primary production trends in forest and shrub vegetation across southwest Western Australia

Abstract

Climate conditions in Mediterranean ecosystems have undergone and are projected to undergo significant change in the future. In the southwest of Western Australia, a number of endemic tree species have experienced significant declines in health and mortality since the early 1990s primarily due to these climatic changes. These health declines are likely to have flow-on effects to regional biodiversity as well as the carbon sequestration potential of the woody vegetation in this region. We report on analysis examining trends in Net Primary Production (NPP) of the woody vegetation in the southwest Australia (SWAU) ecoregion from 2000-2011. To do so, we examine NPP estimates derived from satellite imagery and climate data to answer the questions: (1) what is the extent and rate of change in NPP for the SWAU region over the study period, and (2) how important is fire as a contributing factor in the observed trends. Our results suggest that between 2000-2011, overall NPP declined across the region, with the majority of declines occurring in the transition zone between tree-dominated vegetation and shrublands. Fire attributed for just over 25% to the observed declines. The overall rate of NPP decline for the region was estimated to be-0.38 megaton C per year since 2000. Under the current climate change projections, the declining trends are likely to continue and our results suggest that a shift from tree-dominated to lower shrub-dominated vegetation is occurring, gradually decreasing the carbon storage potential in this region