Ecological Society of America
Rates and spatial patterns of tree mortality are predicted to change during forest structural development. In young forests, mortality should be primarily density dependent due to competition for light, leading to an increasingly spatially uniform pattern of surviving trees. In contrast, mortality in old-growth forests should be primarily caused by contagious and spatially auto-correlated agents (e.g., insects, wind), causing spatial aggregation of surviving trees to increase through time. We tested these predictions by contrasting a three-decade record of tree mortality from replicated mapped permanent plots located in young (<60-year-old) and old-growth (>300-year-old) Abies amabilis forests. Trees in young forests died at a rate of 4.42% per year, whereas trees in old-growth forests died at 0.60% per year. Tree mortality in young forests was significantly aggregated, strong density dependent, and caused live tree patterns to become more uniform through time. Mortality in old-growth forests was spatially aggregated, but was density independent and did not change the spatial pattern of surviving trees. These results extend current theory by demonstrating that density-dependent competitive mortality leading to increasingly uniform three spacing in young forests ultimately transitions late in succession to a more diverse tree mortality regime that maintains spatial heterogeneity through time.
© 2015 by the Ecological Society of America
Andrew J. Larson, James A. Lutz, Daniel C. Donato, James A. Freund, Mark E. Swanson, Janneke HilleRisLambers, Douglas G. Sprugel, and Jerry F. Franklin 2015. Spatial aspects of tree mortality strongly differ between young and old-growth forests. Ecology 96:2855–2861. http://dx.doi.org/10.1890/15-0628.1