Modelling the effects of 'haze' on oil palm productivity and yield.

* 21 Hurrell Road, Cambridge CB4 3RQ UK. A n increasing incidence ofatmospheric pollution in the Southeast Asian region leading to substantial reductions in solar radiation has promoted concern over the possible long term effects on oil palm yields. Previous models of oil palm growth and production have emphasized the importance for yield of adequate radiation but effects of reduced radiation on yield are not immediately apparent due to the long time required for bunch morphogenesis, the complexity of the process and-the presence of assimilate stores which serve to buffer the palm against periods of adverse conditions. Because climatic factors other than radiation influence the physiological processes on which productivity is dependent, models were deueloped to take into account the other main factors, namely, temperature, atmospheric oapourpressure deficit (VPD) and soil water auailability. Temperature had only a small effect because variations in mean temperatures were small. Soil water availability had a larger influence but VPD was the most important factor influencing yields. A lower VPD, lower temperature and improved soil water supply associated with reduced radiation tended to offset yield reductions due to lower light intensity. Under certain conditions, predicted yields were higher under low or moderate than under high radiation. High radiation was associated with high euapotranspiration (ET) rates and lower rainfall, leading to increasing likelihood ofsoil water