Spatially nonrandom tree mortality and ingrowth maintain equilibrium pattern in an old-growth Pseudotsuga-Tsuga forest
Mortality processes in old-growth forests are generally assumed to be driven by gap-scale disturbance, with only a limited role ascribed to density-dependent mortality, but these assumptions are rarely tested with data sets incorporating repeated measurements. Using a 12-ha spatially explicit plot c...
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Published in: | Ecology (Durham) 2014-08, Vol.95 (8), p.2047-2054 |
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Main Authors: | , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Mortality processes in old-growth forests are generally assumed to be driven by gap-scale disturbance, with only a limited role ascribed to density-dependent mortality, but these assumptions are rarely tested with data sets incorporating repeated measurements. Using a 12-ha spatially explicit plot censused 13 years apart in an approximately 500-year-old
Pseudotsuga
-
Tsuga
forest, we demonstrate significant density-dependent mortality and spatially aggregated tree recruitment. However, the combined effect of these strongly nonrandom demographic processes was to maintain tree patterns in a state of dynamic equilibrium. Density-dependent mortality was most pronounced for the dominant late-successional species,
Tsuga heterophylla
. The long-lived, early-seral
Pseudotsuga menziesii
experienced an annual stem mortality rate of 0.84% and no new recruitment. Late-seral species
Tsuga
and
Abies amabilis
had nearly balanced demographic rates of ingrowth and mortality. The 2.34% mortality rate for
Taxus brevifolia
was higher than expected, notably less than ingrowth, and strongly affected by proximity to
Tsuga
. Large-diameter
Tsuga
structured both the regenerating conspecific and heterospecific cohorts with recruitment of
Tsuga
and
Abies
unlikely in neighborhoods crowded with large-diameter competitors (
P
< 0.001). Density-dependent competitive interactions strongly shape forest communities even five centuries after stand initiation, underscoring the dynamic nature of even equilibrial old-growth forests. |
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ISSN: | 0012-9658 1939-9170 |
DOI: | 10.1890/14-0157.1 |