Integration of 3-PG into SWAT to simulate the growth of evergreen forests

SWAT cannot accurately simulate the seasonal fluctuations or the long-term trend of the Leaf Area Index (LAI) of evergreen forests. This deficiency has detrimental impacts for the prediction of interception and transpiration, two processes that have a significant influence on catchment water yield. This paper details the integration of the forest growth model 3-PG with SWAT to improve the simulation of LAI for evergreen forests. The integrated model, called SWAT/3-PG, was applied to the Woady Yaloak River Catchment in southern Australia where eucalyptus forests and pine plantations account for 30% of the total land use. SWAT/3-PG simulated the LAI of eucalypts and pines more accurately and realistically than the original version of SWAT. Forest LAI simulated by SWAT/3-PG agreed reasonably well with estimates of forest LAI derived independently from a Landsat satellite image. SWAT/3- PG has considerable value as a tool that managers can utilise to predict the impacts of land use change in catchments where evergreen forests are prevalent.