What was done
In the words of the authors, "a Holocene fire history of dry heath forests of Cladina and Empetrum-Vaccinium types in eastern Finland was reconstructed on the basis of charcoal layer data from two small mire basins and fire scars in living and dead pines."

What was learned
Pitkanen et al. report that "in natural conditions after the establishment of spruce (about 6300 cal. yr. BP) Cladina and Empetrum-Vaccinium sites burned at an average interval of 170-240 years, which is 3-8 times longer than the average intervals of 30-50 years put forward in fire scar studies covering the past few centuries," which finding they say is indicative of "a changeover to a human influenced fire regime."  Superimposed upon these background fire frequencies, the authors found a "decrease in fires during climatic warming in the Atlantic chronozone (about 9000-6000 cal. yr. BP)," noting that "the very low fire frequency during the Atlantic chronozone despite climatic warming with higher summer temperatures, is contrary to assumptions about possible implications of the present climatic warming due to greenhouse gasses (e.g. Overpeck et al., 1990; Fosberg et al., 1996; Wein and de Groot, 1996)."  They also observed a change in fire frequency at the transition between the Atlantic and Subboreal chronozones around 6000 cal. yr. BP, noting that "the climatic change that triggered the increase in fire frequency was cooling and a shift to a more continental climate."  In addition, they report that the data of Bergeron and Archambault (1993) and Carcaillet et al. (2001) from Canada suggest much the same thing, i.e., less boreal forest fires during periods of greater warmth.

What it means
"As regards the concern that fire frequency will increase in [the] near future owing to global warming," the authors say their data "suggest that fires from 'natural' causes (lightening) are not likely to increase significantly in eastern Finland and in geographically and climatically related areas (Fennoscandia and northwest Russia)."  Neither do they seem likely to increase in eastern Canada.

References
Bergeron, Y. and Archambault, S.  1993.  Decreasing frequency of forest fires in the southern boreal zone of Quebec and its relation to global warming since the end of the "Little Ice Age."  The Holocene 3: 255-259

Carcaillet, C., Bergeron, Y., Richard, P.J.H., Frechette, B., Gauthier, S. and Prairie, Y.  2001.  Change of fire frequency in the eastern Canadian boreal forests during the Holocene: Does vegetation composition or climate trigger the fire regime?  Journal of Ecology 89: 930-946.

Fosberg, M.A., Stocks, B.J. and Lynham, T.J.  1996.  Risk analysis in strategic planning.  In: Goldammer, J.G. and Furyaev, V.V. (Eds.), Fire in Ecosystems in Boreal Eurasia, Kluwer, Dordrecht, The Netherlands, pp. 495-504.

Overpeck, J.T., Rind, D. and Goldberg, R.  1990.  Climate induced changes in forest disturbance and vegetation.  Nature 343: 51-53.

Wein, R.W. and de Groot, W.J.  1996.  Fire-climate hypotheses for the taiga.  In: Goldammer, J.G. and Furyaev, V.V. (Eds.), Fire in Ecosystems in Boreal Eurasia, Kluwer, Dordrecht, The Netherlands, pp. 505-512.