- 1Institute
of Silviculture, Department of Forest- and Soil Sciences, University of
Natural Resources and Life Sciences, 1190 Vienna, Austria;
rupert.seidl@boku.ac.at turnermg@wisc.edu.
- 2Department of Zoology, University of Wisconsin-Madison, Madison, WI 53706.
- 3Washington State Department of Natural Resources, Olympia, WA 98504.
- 4Department of Entomology, University of Wisconsin-Madison, Madison, WI 53706.
- 5Department of Zoology, University of Wisconsin-Madison, Madison, WI 53706; rupert.seidl@boku.ac.at turnermg@wisc.edu.
Abstract
Climate
change is altering the frequency and severity of forest disturbances
such as wildfires and bark beetle outbreaks, thereby increasing the
potential for sequential disturbances to interact. Interactions can
amplify or dampen disturbances, yet the direction and magnitude of
future disturbance interactions are difficult to anticipate because
underlying mechanisms remain poorly understood. We tested how
variability in postfire forest development affects future susceptibility
to bark beetle outbreaks, focusing on mountain pine beetle
(Dendroctonus ponderosae) and Douglas-fir beetle (Dendroctonus
pseudotsugae) in forests regenerating from the large high-severity fires
that affected Yellowstone
National Park in Wyoming in 1988. We combined extensive field data on
postfire tree regeneration with a well-tested simulation model to assess
susceptibility to bark beetle outbreaks over 130 y of stand
development. Despite originating from the same fire event, among-stand
variation in forest structure was very high and remained considerable
for over a century. Thus, simulated emergence of stands susceptible to
bark beetles was not temporally synchronized but was protracted by
several decades, compared with stand development from spatially
homogeneous regeneration. Furthermore, because of fire-mediated
variability in forest structure, the habitat connectivity required to
support broad-scale outbreaks and amplifying cross-scale feedbacks did
not develop until well into the second century after the initial burn.
We conclude that variability in tree regeneration after disturbance can
dampen and delay future disturbance by breaking spatiotemporal synchrony
on the landscape. This highlights the importance of fostering landscape
variability in the context of ecosystem management given changing
disturbance regimes.
KEYWORDS:
disturbance interactions; forest dynamics; heterogeneity; landscape ecology; lodgepole pine