Competition and climate influence growth of black spruce in western boreal forests

Abstract

The effects of competition and climate on the growth of black spruce (Picea mariana (Mill.) BSP.) were examined using long term measurement data collected across the western Canadian boreal forest. Non-linear mixed effect models were developed and used to examine tree growth responses to competition and climate across the range of upland forest types where black spruce is found in this region including: spruce/fir, deciduous and pine forest types. Basal area of competitor trees larger than the subject tree, and at least one of the following climate variables: frost free period, mean annual precipitation and mean annual temperature, were selected as predictors of diameter and height growth. Spruce/fir competition had a stronger negative effect on the growth of black spruce than pine competition. However, deciduous competition had a positive effect on diameter and height growth of black spruce. Growth was generally sensitive to changes in climate across the three forest types. Increases in temperature (except in pine forest stand) and reductions in precipitation (except in deciduous forest stand) lead to increases in diameter and height growth; however, our model also predicted that increasing temperature when pine stand densities are high will lead to a reduction in growth. These results indicated that forest types and competition will determine the impact of climate on the growth of black spruce trees. Climate sensitive growth functions developed for black spruce in this study will be useful in modeling and managing pure and mixed stands of black spruce across the western boreal forest.