Modelling the effects of needle mortality rate and needle area distribution on dry matter production of Douglas fir

Abstract

A physiological simulation model is used to analyse the effects of increased needle mortality rate and changes in needle area distribution on the primary production of Pseudotsuga menziesii stand. Needle life-span may decrease as a result of air pollution and soil acidification, and is an important aspect of forest decline. The model is used to quantify the relationship between total leaf area index (LAI) and stand growth, taking into account different light distributions within the canopy that result from needle area distribution and clustering of needles. At low initial LAI, productivity will decrease as a result of an increase in needle mortality and decreased light interception; at high initial LAI, light interception does not necessarily decrease significantly when needle mortality increases, but productivity may even increase because of decreased maintenance respiration. -from Authors