MODELING PRODUCTIVITY AND TRANSPIRATION OF PINUS-RADIATA - CLIMATIC EFFECTS

Climatic effects on annual net carbon gain, stem biomass and annual tr anspiration were simulated for Pinus radiata D. Don at Canberra and Mt . Gambler Simulations were conducted with an existing process-based fo rest growth model (BIOMASS, Model 1) and with a modified version of th e BIOMASS model (Model 2) in which response functions for carbon assim ilation and leaf conductance were replaced with those derived from fie ld gas exchange data collected at Mt. Gambler. Simulated carbon gain w as compared with a published report stating that mean annual stem volu me increment (MAI) at Mt. Gambler was 1.8 times greater than at Canber ra and that the difference could be the result solely of differences i n climate. Regional differences in climate resulted in a 20% greater s imulated annual transpiration at Canberra than at Mt. Gambler but only small differences in simulated productivity, indicating that climatic differences did not account for the reported differences in productiv ity. With Model 1, simulated annual net carbon gain and annual increas e in stem biomass were greater at Canberra than at Mt. Gambler, wherea s Model 2 indicated a similar annual net carbon gain and annual stem b iomass increase in both regions.