Detecting Local Drivers of Fire Cycle Heterogeneity in Boreal Forests: A Scale Issue

Abstract

Abstract:Severe crown fires are determining disturbances for the composition and structure of boreal forests in North America. Fire cycle (FC) associations with continental climate gradients are well known, but smaller scale controls remain poorly documented. Using a time since fire map (time scale of 300 years), the study aims to assess the relative contributions of local and regional controls on FC and to describe the relationship between FC heterogeneity and vegetation patterns. The study area, located in boreal eastern North America, was partitioned into watersheds according to five scales going from local (3 km 2 ) to landscape (2800 km 2 ) scales. Using survival analysis, we observed that dry surficial deposits and hydrography density better predict FC when measured at the local scale, while terrain complexity and slope position perform better when measured at the middle and landscape scales. The most parsimonious model was selected according to the Akaike information criterion to predict FC throughout the study area. We detected two FC zones, one short (159 years) and one long (303 years), with specific age structures and tree compositions. We argue that the local heterogeneity of the fire regime contributes to ecosystem diversity and must be considered in ecosystem management.

Accounting for spatial autocorrelation improves the estimation of climate, physical environment and vegetation’s effects on boreal forest’s burn rates

“…Previous studies at local scales in eastern Canada have shown that SDs influence fire cycles (Mansuy et al 2010;Bélisle et al 2016). At our larger scale, LDs dominated by SDs presenting a coarse or medium texture were the most likely to have a nonnull BR, followed by LDs dominated by bedrock, and finally LDs dominated by fine texture SDs or organic deposits.…”

“…Low hills and hills are mostly found on thick till deposits with coarse or medium textures (Robitaille et al 2015) that facilitate fire spread. In contrast, high hills and mounts are generally found on thin tills and bedrock in rugged landscapes that can act as firebreaks (Bélisle et al 2016). Moreover, high hills and mounts most often have a higher elevation than the other two relief classes.…”

Fire Regime along Latitudinal Gradients of Continuous to Discontinuous Coniferous Boreal Forests in Eastern Canada

“…The region is also characterized by an important variability of surficial deposits, from organic deposits and bedrock to till dominance from south to north [49]. Topography and surficial deposits are two significant factors of fire risk because they influence the drying potential of the forest floor as well as fuel composition and structure [14,18,40]. Well-drained stands are more likely to burn [18], and the slopes found in the northern portion of the transect could, for example, help with draining and thus drying the forest floor, thereby facilitating fire spread.…”

“…Fires also influence stands' composition by controlling succession patterns, for instance, by favoring fire-adapted species such as jack pine (Pinus banksiana) or black spruce (Picea mariana) [9][10][11]. Fire regimes are highly variable in space as a result of various environmental factors acting on different scales [12][13][14]. Climate acts as a top-down factor from regional to continental scales.…”

“…In Canada, for instance, the increasing gradient of fire activity observed from east to west is caused by the spatial variability in the frequency of drought events [15,16]. However, topography [14,17], surficial deposits and drainage [18], or fuel type and availability [19] are bottom-up factors which act from stand to regional scales. Fire regimes also vary in time; for example, the end of the Little Ice Age that occurred around 1850 represents a well-known transition to lower fire cycles in eastern Canada [8,20].…”