Data from: Fire history in a western Fennoscandian boreal forest as influenced by human land use and climate

Knowing the historical variation in fire regimes is instrumental in
managing forests today and in predicting what may happen in the future. By
cross-dating 745 fire scars in 378 samples of remnant Scots pines, we
delineated 254 individual forest fires during the past 700 years in a
74-km2 section of Trillemarka-Rollagsfjell Nature Reserve in south-central
Norway. Fire sizes, numbers, burn rates, and frequencies were compared
with historical climate proxies, vegetation maps, and written sources. The
results revealed patterns consistent with a predominantly climate-driven
fire regime up to 1625, followed by periods of strong anthropogenic
influence that increased fire frequency during 1600–1700s and diminished
fires during 1800–1900s. This was documented by an abrupt increase in
number of small fires from the early 1600s that markedly shortened fire
intervals from a median of 73 to 37 yr. This shift in fire frequency
coincided with a sudden appearance of early-season fires from 1625 and
onward. Whereas late-season burn rate increased with summer temperature,
no such relationship was found for early-season fires. These results were
corroborated by written sources that describe anthropogenic forest fires
and slash-and-burn cultivation expanding with the increasing population
from the late 1500s and subsequently diminishing due to increasing timber
values during 1700–1800s. Whereas human activity strongly influenced the
fire regime at multidecadal to centennial scales, it was the interannual
variability in climate that triggered large fire events, especially during
the pre-1625 period. Prior to 1625, the percentage of years with fire
tripled from 7% during cold summers (10–12°C) to 21% during warm summers
(14–16°C). Burn rate increased even more, from 0.01% to 1.3% for the same
temperature intervals. Ecologically, the post-1625 period is remarkable in
such a way that human activity, first by greatly increasing fire frequency
and subsequently almost eradicating fires, possibly influenced the fire
regime to such an extent that it may be unprecedented for millennia.