Spatially nonrandom tree mortality and ingrowth maintain equilibrium pattern in an old-growth Pseudotsuga-Tsuga forest

James A. Lutz, Andrew J. Larson, Tucker J. Furniss, Daniel C. Donato, James A. Freund, Mark E. Swanson, Kenneth J. Bible, Jiquan Chen, Jerry F. Franklin

Research output: Contribution to journalArticlepeer-review

Abstract

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 latesuccessional 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). Densitydependent competitive interactions strongly shape forest communities even five centuries after stand initiation, underscoring the dynamic nature of even equilibrial old-growth forests.

Original languageEnglish
Pages (from-to)2047-2054
Number of pages8
JournalEcology
Volume95
Issue number8
DOIs
StatePublished - Aug 2014

Keywords

  • Abies amabilis
  • Long-term data sets
  • Pseudotsuga menziesii
  • Taxus brevifolia
  • Tree mortality
  • Tsuga heterophylla
  • Wind River Forest Dynamics Plot

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