Estimating branch production in trembling aspen, Douglas-fir, jack pine, black spruce, and balsam fir

Abstract

Measuring net primary productivity of trees requires the measurement of total wood production of branches. Recent work on balsam fir ( Abies balsamea ) has shown that branch-wood production can be estimated as a function of foliage production. We extend the analysis to four other species found in the Canadian forest: black spruce ( Picea mariana ), jack pine ( Pinus banksiana ), Douglas-fir ( Pseudotsuga menziesii ), and trembling aspen ( Populus tremuloides ). Results show that the ratio of annual branch-wood production to annual foliage production is about 1.0 for conifer species (between 0.86 and 1.12) and 0.56 for aspen during a nondrought year. An analysis using field measurements of litterfall and stem-diameter increment from selected forested sites shows that branch-wood production accounts for a smaller proportion of aboveground net primary productivity in trembling aspen (15%–20%) than in conifer species (25%). Also, litterfall capture of small branches (<1 cm diameter) accounts for only 33% of branch detritus production in conifers and 50% in trembling aspen. This study supports the use of an alternative method for estimating branch-wood production that reduces the potential bias in field estimates of net primary productivity.