Data from: Postglacial climate and fire-mediated vegetation change on the western Olympic Peninsula, Washington

The mode and tempo of forest compositional change during periods of rapid
climate change, including the potential for the fire regime to produce
non-linear relationships between climate and vegetation, is a
long-standing theme of forest ecological research. In the old conifer
forests of the coastal Pacific Northwest, fire disturbances are
sufficiently rare that their relation to climate and their ecological
effects are poorly understood. We used a 14,700-year high-resolution
sediment record from Yahoo Lake on the Olympic Peninsula to examine
vegetation (landscape vegetation from pollen and local vegetation from
macrofossils) and fire (landscape fire from total charcoal and local fire
from charcoal peaks) in conjunction with independent records of climate.
We hypothesized that the successional stage of the local forest will
exhibit alternate stable states over a range of fire activity, that
species turnover will increase abruptly above a certain level of fire
activity and that both responses would be more gradual at the landscape
scale than the local scale. Supporting these hypotheses, at the local
scale we found strong evidence for alternate stable states of late vs.
early successional communities and inertia of species turnover to changing
fire activity. At the landscape scale, vegetation responded more gradually
to changing fire activity. From 14,700 to 7000 years ago, high landscape
vegetation turnover occurred along with high landscape fire activity,
especially during the warm summers of the early Holocene. In several
instances local species turned over completely following fire events but
several centuries after climate change. In contrast, during the last 7000
years the local forest composition was dominated by late-successional
species with little species turnover despite periods of moderate fire
activity. We suggest that the relatively minor climate fluctuations of the
past 7000 years were not sufficient to cause large-scale species turnover
after fire. The Yahoo Lake fire and vegetation record of the early
Holocene provides a model for dramatic ecosystem change following an
anticipated shift to warmer summer temperatures.