Forest production dynamics along a wood density spectrum in eastern US forests

Abstract

Key message Emerging plant economics spectrum theories were confirmed across temperate forest sys- tems of the eastern US where the use of a forest stand's mean wood density elucidated forest volume and bio- mass production dynamics integrating aspects of cli- mate, tree mortality/growth, and rates of site occupancy. Abstract As a tree's functional trait of wood density has been used to refine models of tree competition, it may also aid in evaluating hypotheses of forest production such as declining growth and mortality across a spectrum of increasing wood density. The goal of this study was to examine trends in aboveground live tree production as related to mean wood density using a region-wide repeated forest inventory across eastern US forests. Using quantile regression, the 90th percentile of volume and biomass accretion was negatively related to the mean wood density of a stand's constituent tree species. This relationship was strongest on forest sites with the highest number of growing season degree days, as growing season length influences the rates of stand development. For these sites, variations in volume and biomass accretion were most pronounced in stands with low mean tree wood density, which also demonstrated the highest rates of site occu- pancy and mortality. This study confirmed aspects of the emerging theory of ''fast-slow'' plant economics spec- trums across temperate forest ecosystems. Stands with relatively low wood density appear to occupy sites more rapidly leading to a concomitantly higher rate of tree mortality, but with less biomass accretion relative to vol- ume due to allocating biomass or carbon to a greater tree volume. In contrast, stands with higher wood density exhibited slower site occupancy due to high wood density construction costs, but with increased biomass relative to volume accretion. These findings highlight the potential application of the plant economics spectrum theory in refining our understanding of general patterns of forest stand production, the role of plant traits in forest man- agement, and knowledge gaps such a shifts in tree allom- etry during stand development.