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

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.