Geoscience Reference
In-Depth Information
Chapter 9
Climatic Inferences from Dendroecological
Reconstructions
Thomas W. Swetnam and Peter M. Brown
Abstract
Tree rings have long been employed by ecologists to study the local-
scale dynamics of forest stands and woodlands, but only recently have network
approaches been applied to evaluate regional and broader-scale processes. As
with dendroclimatic data (e.g., ring-width and ring-density chronologies), cli-
matic drivers become much more evident in dendroecological data aggregated at
broad spatial scales (relative to local-scale data). Study of dendroecology net-
works has led to new insights on climatic variability and change and their impacts
on ecosystems. In addition to the power of network approaches, dendroecology
has advanced in recent decades because of the ready availability of, and com-
parison with, high quality, independent dendroclimatic reconstructions of various
hydro-climatic parameters (e.g., drought indices, precipitation and temperature) and
ocean-atmosphere indices (e.g., ENSO, PDO, and AMO). Dendroecological recon-
structions that have been most commonly employed in climate-related analyses are
disturbance histories (e.g., fire and insect outbreaks). We review examples of these
applications from our studies in the Southwestern United States. We also compile
and describe here, for the first time, a regional network of ponderosa pine (
Pinus
ponderosa
) establishment dates from the Southwest, and we show that episodic
natality patterns are probably associated with decadal wet periods. Using another
example of decadal variability in forest fire histories—specifically a hiatus in fire
occurrence in the circa 1780-1840 time period—we make a case that regional
to continental-scale dendroecological reconstructions can provide useful insights
about 'ecologically-effective climate change'. We define this type of climatic vari-
ability as the patterns of climate at interannual, decadal and centennial scales that
are most distinctly reflected in synchronous ecological responses at regional and
broader scales. In the context of dendroclimatology, primary values of the investiga-
tion of specific climatic patterns that elicit regional and broader ecological responses
