[MCN] Thinning: Young trees in dense stands die in competition for light

[Lance Olsen]

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


Abstract bold added
http://www.esajournals.org/doi/abs/10.1890/15-0628.1

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 autocorrelated 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, strongly 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 tree spacing in young 
forests ultimately transitions late in succession to a more diverse 
tree mortality regime that maintains spatial heterogeneity through 
time.
-- 
"Climate change will alter ecosystem services, perceptions of value, 
and decisions regarding land uses. Outcomes for people will be 
determined by the interaction between changes in biophysical 
environments (e.g., climate, disturbance, and invasive species) and 
human responses to those changes (management and policy)."

United States Department of Agriculture
Forest Service
Pacific Northwest Research Station
General Technical Report PNW-GTR-870
December 2012
http://www.fs.fed.us/pnw/pubs/pnw_gtr870/pnw_gtr870.pdf
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