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

Abstract

A physiological simulation model was used to analyse the effects of increased needle mortality rate and changes in needle area distribution (LAI) on primary production of a Douglas fir (Pseudotsuga menziesii) stand. Needle life-span, which may decrease as a result of air pollution and soil acidification, is an important aspect of forest decline. Results show that simulation models can be used to study the possible consequences of these phenomena in forest stands. The model quantified the relationship between total LAI and stand growth (taking into account different light distributions within the canopy that result from needle area distribution and clustering of needles). The effect of an increase in needle mortality rate was strongly dependent on initial LAI: 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. These effects are discussed, and compared with other species, such as Scots pine (Pinus sylvestris) which has a relatively low LAI. The authors recommend using more quantitative techniques in forest decline inventories (e.g. estimating LAI from light interception measurements) in order to account for these LAI differences. (Abstract retrieved from CAB Abstracts by CABI’s permission)