At the 2019 Fall Fire Science Workshop, we had a great presentation by Jill Johnstone on the concept of fire self-regulation in the boreal forest*. This theory holds that as fire becomes more frequent and/or severe, spruce forests will increasingly convert to mixed and deciduous forests and provide negative feedback to burn extent even as the climate warms.
As you heard there, Jill is spearheading an effort to do a synthesis of findings of many studies in AK/Canada. At last week’s Association of Fire Ecology (AFE) Congress meeting, team member Xanthe Walker shared preliminary findings of the search for evidence of the effects of stand age and alternative vegetation types on probability of burning. Do fires seem to “prefer” or “avoid” areas which burned in recent history? In short, several studies across Canada, and a couple from Alaska, provide evidence for some level of self-regulation. That begs the question: how important are fuels vs. weather? Will the self-regulation effect be enough to moderate the influence of higher fire indices in the future on acres burned?
Recall that fairly rigid self-regulatory feedbacks were programmed into the Boreal ALFRESCO model that has been used by Rupp, Duffy, Shultz, and others to build scenarios for Alaska’s land managers on how much burning will occur in the future and how much that will cost in suppression effort. (See Implications of Climate and Management Options on Wildland Fire in Alaska: Exploring Future Fire Scenarios, a presentation by Courtney Schultz and Tait Rutherford at the 2017 Alaska Fall Fire Science Workshop, October 10, 2017.) But, can we count on this? Xanthe’s presentation (which AFSC recorded at the meeting and will soon be posting for you on our Vimeo site) concluded there will be SOME moderation of increased burning but also that these fuel effects can be overwhelmed by weather. The latter is no surprise to fire practitioners in Alaska, i.e. young stands burn in extreme fire years and deciduous stand burn more during drought years. Quantifying this effect is what we need, and some good studies are starting to emerge. Across the North American boreal forest, it appears that the strongest self-regulation occurs when weather is not extreme and where deciduous forests dominate to begin with. It’s great to have a start on the answer to our burning questions about re-burn—there is clearly more to discover and we’re tickled to have this power-house team of researchers working on the problem. You better believe we’ll be keeping in touch and watching for their publications. We’re also happy they have welcomed the participation of agency fire ecologists and other local practitioners into the studies, because folks in the field have a lot to bring to the observational table.
*See Fire Self-Regulation, Evaluating the Current State of Understanding from Published Studies Presented by: Jill Johnstone, University of Alaska Fairbanks and University of Saskatchewan at the October 2019 AWFCG Fall Fire Review
List of selected citations used in Walker presentation:
Beverly, J. L. 2017. Time since prior wildfire affects subsequent fire containment in black spruce. International Journal of Wildland Fire 26:919–929. (Assesses whether stand age of black spruce forests has a detectable effect on the success of initial attack on fires <2 ha size in Alberta.)
Boulanger, Y. et al. 2017. Changes in mean forest age in Canada’s forests could limit future increases in area burned but compromise potential harvestable conifer volumes. Canadian Journal of Forest Research 47(6): 755-764. (Modeled fire occurrence in the face of climate change with inclusion of self-regulation due to vegetation change across fire regimes of Canada. Self-regulation substantially moderated the climate-driven fire increases but did not fully compensate for it – so fire activity will still increase even with the inclusion of these feedbacks).
Dash, C. B., J. M. Fraterrigo, and F. S. Hu. 2016. Land cover influences boreal-forest fire responses to climate change: geospatial analysis of historical records from Alaska. Landscape Ecology 31:1781–1793. (Large fires had a greater proportion of conifer forests than small fires, suggesting preferential rapid fire spread in conifer forests, but the effect of land cover on burning is less in years with extreme fire weather, when vegetation types burn at a rate close to that expected in the random model.)
Erni, S., D. Arseneault, M.-A. Parisien, and Y. Begin. 2017. Spatial and temporal dimensions of fire activity in the fire‐prone eastern Canadian taiga. Global Change Biology 23:1152–1166. (Firescar study of reconstructed 300 years of fire activity in Quebec to examine relative effects of climate/ weather vs. forest age controls on fire activity. In younger stands, burn rate was lower for up to 50 years, depending on landscape).
Hely, C., M. D. Flannigan, Y. Bergeron, and D. J. McRae. 2001. Role of vegetation and weather on fire behavior in the Canadian mixedwood boreal forest using two fire behavior prediction systems. Canadian Journal of Forest Research, v. 31, no. 3, p. 430-441. (Compared FBP and Behave performance in boreal mixedwood in Quebec. Although weather was overall more influential than fuel type, expected ROS was lower in deciduous that coniferous stands, and FBP performed better than Behave in this fueltype).
Parks, S. A., M.-A. Parisien, C. Miller, L. M. Holsinger, and L. S. Baggett. 2018. Fine-scale spatial climate variation and drought mediate the likelihood of reburning. Ecological Applications 28:573–586. (Fire spread was retarded by presence of previous fires for about 33 years in Wood Buffalo Park, Alberta, but the drought reduced the self-limiting effect of previous fire).