Predicting wood production and net ecosystem carbon exchange of Pinus radiata plantations in south-western Australia: Application of a process-based model

Over much of south-western Australia there was a rapid decrease in rainfall of around 20% in the mid-1970s. Further declines in rainfall are predicted along with increases in temperature and atmospheric CO₂ concentration. This study focused on the implications of such a change for wood production and net ecosystem carbon exchange of pine plantations in that region. The process-based model CenW was evaluated using measurements of basal area and soil moisture in Pinus radiata plantations at seven sites in south-western Australia, encompassing a range of climatic conditions and silvicultural treatments (fertiliser application and thinning). The model predicted basal area very well and soil moisture reasonably well, except for one site where a water table may have provided additional water supply to trees. The model was then applied to assess the effects of the climatic changes that have occurred since 1975 by running the model for whole 30-year rotations, using observed climate data from either the 1945-1975 or 1975-2005 periods. The simulations showed that out of the six sites considered, wood production and net ecosystem carbon exchange were increased in the latter period at three sites, remained almost unchanged at two sites, and decreased at one site. Analysis of the model outputs, aided by additional simulations revealed that the response to the climate shift was determined by soil type (i.e. decreased growth rate was confined to the site with a sandy soil), and by the interaction between rising CO₂ levels (positive effect) and changes in rainfall (positive or negative depending on the direction of the change in rainfall).