Geoscience Reference
In-Depth Information
Fig. 3.3
LANDFIRE data mapping Washington State's Mean Fire Return Interval, which quanti-
fies the average period between fires under presumed historical fire regimes. (Graphics by Jacob
Lesser)
moisture levels in these seasons may transfer heat far better than dry summer soils,
allowing the less intense prescribed fires to kill the roots of plants that would have
survived more intense summer fires.
Even in the face of significant climate change, a strong argument can be made
that understanding the historical patterns of ecosystems is critical for effective man-
agement (Swetnam et al.
1999
). However, when historical records are not available,
or do not extend long enough to be of use in understanding fire history, the most
common tool is Dendrochronology. It is far beyond the scope of this chapter to
expand on the field or statistical techniques of Dendrochronologists, but excellent
texts are available.
The discipline was developed in the early 20th century by the astronomer
A.E. Douglas. Douglas was trying to demonstrate that sunspots affected climate
and therefore the width of annual growth rings in trees. He went on to estab-
lish the Laboratory of Tree-Ring Research at the University of Arizona in 1937.
Dendrochronology has moved far beyond simply estimating the annual growing
conditions encountered by single trees. In fact, the discipline has developed into
a powerful geographic tool. Not only has it been central in determining the fire
return patterns for many areas of the world, it has become a powerful tool in climate
reconstruction and was even central in unraveling mysteries such as the nature of the
relationship between North American climate and the El Niño Southern Oscillation
in the southern Pacific (Swetnam and Betancourt
1990
).
3.4.4 Scale
The final element of fire regimes is scale. Fire regimes can be classified by referring
to the expected size of fires. Once again, this simple concept can require consider-
able expansion. Like MFRI, there may be unstated variability around mean fire size
