A Century of Forest Change

Network News Summer 2015, Vol. 28 No. 2
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In ecological research, it’s rare to have a century-long record. But the Andrews Forest team has just that from three plots, established in April 1910 in the Willamette National Forest, by pioneer Pacific Northwest forester, T.T. Munger (see Fall 2010 Andrews Forest newsletter). Andrews Forest (AND) Long Term Ecological Research (LTER) scientists Mark Harmon and Rob Pabst recently used data from these plots to publish a new paper analyzing records of tree establishment, growth, and death observed at 5–10 year intervals as the stands aged from 54 to 154 years. Predictions about population, community, and ecosystem change over this time period have been primarily based on “chronosequence” studies—trading space for time—by examining variation among stands of different ages but in similar environments.

Comparing these predictions with plot records, Mark and Rob find the predictions hold up for change over time of plant populations (e.g., Douglas-fir stem density decreases over time) and community structure (e.g., shade-intolerant Douglas-fir gives way to shade-tolerant tree species). Surprisingly, however, at the ecosystem level, live stand biomass constantly increased over the century of record—much longer than predicted from ecosystem theory, which suggests that increasing mortality would slow the rate of biomass accumulation.

Andrews Forest ecologists are tracking 79 additional old plots (75–100 years old) on five other national forests in the region, which will yield tests of these findings. See the full article, Testing predictions of forest succession using long-term measurements: 100 yrs of observations in the Oregon Cascades