Changes in fire regime explain the Holocene rise and fall of Abies balsamea in the coniferous forests of western Quebec, Canada (original) (raw)
Related papers
Fire Regimes at the Transition Between Mixedwood and Coniferous Boreal Forest in Northwestern Quebec
Ecology, 2004
Fire history was reconstructed for an area of 15 000 km 2 located in the transition zone between the mixed and coniferous forests in Quebec's southern boreal forest. We used aerial photographs, archives, and dendroecological data (315 sites) to reconstruct a stand initiation map for the area. The cumulative distribution of burnt area in relation to time since fire suggests that the fire frequency has decreased drastically since the end of the Little Ice Age (about 1850) in the entire region. However, a large part of the area was burned between 1910 and 1920 during intensive colonization and when the climate was very conducive to fire. For the period 1920-1945, large fires have mainly been concentrated in the more populated southern area, while few fires have been observed in the virgin coniferous forest in the north. Despite slight differences between the south and the north, fire cycles or the average number of years since fire are not significantly different. Since 1945, there have been far more fires in the south, but the mean fire size was smaller than in the north. These results suggest that the transition between the mixed and coniferous forests observed in the southern boreal forest cannot be explained by a difference in fire frequency, at least during the last 300 years. As climatic factors and species potential distribution did not vary significantly from south to north, we suggest that the transition from mixedwood to coniferous forests is mainly controlled by fire size and severity. Smaller and less severe fires would favor species associated with the mixedwood forests as many need survivors to reinvade burnt areas. The abundance of deciduous species in mixedwood forests, together with the presence of more lakes that can act as firebreaks, may contribute to decreases in fire size and severity. The transition between the two vegetation zones could be related to the initial setting following the vegetation invasion of the area during the Holocene. In this context, the limit of vegetation zones in systems controlled by disturbance regimes such as fires may not have reached a balance with current climatic conditions. Historical legacies and strong positive feedback between disturbance regimes and composition may filter and delay the responses to changes in climate.
Reconstruction of fire history (1680–2003) in Gaspesian mixedwood boreal forests of eastern Canada
Forest Ecology and Management, 2007
We describe the fire regime in the Gaspesian mixedwood boreal forest in order to improve our knowledge of the maritime fire regime through time and the role of climate on changes in fire cycle. We also investigated the importance of coarse scale spatial factors, such as topography, altitude, soil-type and vegetation-type. Fire history was reconstructed for a 6480-km 2 area using Quebec Ministry of Natural Resource archival data and aerial photographs combined with dendrochronological data, collected using a random sampling strategy. Physiographic features were not found to significantly influence the fire cycle, but an increase in the cycle (from 89 to 176 years p 0.0001) was observed since the end of Little Ice Age (LIA) (1850). Relative agreement between the archival data and the semi-parametric survival analysis approach for the 1850-2003 period provides greater confidence in our determination of a fire cycle situated between 170 and 250 years. An analysis of fluctuations in the Canadian forest fire Weather Index system, calculated for the period 1920-2003, showed a statistically significant decrease in extreme values. Given such a long fire cycle and in the context of forest management based on natural disturbance, even-aged management under short rotations should be questioned in these mixedwood boreal forests. #
Large fires as agents of ecological diversity in the North American boreal forest
International Journal of Wildland Fire, 2008
The present study undertook a hierarchical analysis of the variability within and among some individual fire events in the boreal ecozones of Canada and Alaska. When stratified by ecozone, differences in the spatial and temporal distribution of wildfires were observed in the Canadian Large Fire Data Base that reflect climatic, terrain and land-use differences across the country. Remote-sensing data collected before and after boreal forest fires permitted a rigorous analysis of the variability in burn severity within individual fire events, and the identification of certain fire-prone and more fire-resistant land-cover types. The occurrence of fire skips or islands was related to the distribution of those cover types, resulting in proportionally more unburned area within the perimeter of a burn for larger fires. Differences in burn severity led to differences in post-burn vegetation response of tree, shrub and moss layers that can persist for decades or even centuries. As a result, there can be considerable variability in the survival, density and distribution of residual biota and organic materials. This variability creates a range of post-fire vegetation patterns and contributes much to the habitat diversity of boreal landscapes.
1999
Simulations were carried out in the Fire Behavior Prediction (FBP) and the BEHAVE systems for spring and summer seasons to study the importance of vegetation and climate on fire behavior in the mixedwood boreal forest. Stand were characterized as deciduous, mixed- deciduous, mixed-coniferous, or coniferous stands, if their conifer basal area was respectively less than 25%, between 25 and 50%, between 50 and 75%, or greater than 75% of stand basal area. Sampled fuel loads (litter, duff, woody debris, herbs, and shrubs), and local weather conditions around Lake Duparquet (Quebec, Canada) were input in the simulation systems. The predicted fire behavior variables were Rate of Spread (ROS), Head Fire Intensity (HFI), and burned area. Results from Anovas on ranks showed that the two simulators attribute differently the maximum explained variance to the different factors. Climate is the most important factor for all fire behavior variables with the FBP whereas BEHAVE gives the greatest pa...
Fire Interval Effects on Successional Trajectory in Boreal Forests of Northwest Canada
Ecosystems, 2006
Although succession may follow multiple pathways in a given environment, the causes of such variation are often elusive. This paper describes how changes in fire interval mediate successional trajectory in conifer-dominated boreal forests of northwestern Canada. Tree densities were measured 5 and 19 years after fire in permanent plots and related to pre-fire vegetation, site and fire characteristics. In stands that were greater than 75 years of age when they burned, recruitment density of conifers was significantly correlated with pre-fire species basal area, supporting the expectation of stand self-replacement as the most common successional pathway in these forests. In contrast, stands that were under 25 years of age at the time of burning had significantly reduced conifer recruitment, but showed no change in recruitment of trembling aspen (Populus tremuloides). As a result, young-burned stands had a much higher probability of regenerating to deciduous dominance than mature-burned stands, despite the dominance of both groups by spruce (Picea mariana and Picea glauca) and pine (Pinus contorta) before the fire. Once initiated, deciduous-dominated stands may be maintained across subsequent fire cycles through mechanisms such as low on-site availability of conifer seed, competition with the aspen canopy, and rapid asexual regeneration of aspen after fire. We suggest that climate-related increases in fire frequency could trigger more frequent shifts from conifer to deciduous-dominated successional trajectories in the future, with consequent effects on multiple ecosystem processes.
Boreas, 2014
In boreal forest ecosystems, wildfire severity (i.e. the extent of fire-related tree mortality) is affected by environmental conditions and fire intensity. A burned area usually includes tree patches that partially or entirely escaped fire, called 'residual patches'. Although the occurrence of residual patches has been extensively documented, their persistence through time, and thus their capacity to escape several consecutive fires, has not yet been investigated. Macroscopic charcoal particles embedded in organic soils were used to reconstruct the fire history of 13 residual patches of the eastern Canadian boreal mixedwood forest. Our results display the existence of two types of residual patches: (i) patches that only escaped fire by chance, maybe because of local site or meteorological conditions unsuitable for fire spread (random patches), and (ii) patches with lower fire susceptibility, also called 'fire refuges' that escaped at least two consecutive fires, probably because of particular site characteristics. Fire refuges can escape fire for more than 500 years, up to several thousand years, and probably burn only during exceptionally severe fire events. Special conservation efforts could target fire refuges owing to their old age, long ecological continuity and potential specific biological diversity associated to different microhabitats.
Increasing fire and the decline of fire adapted black spruce in the boreal forest
Proceedings of the National Academy of Sciences, 2021
Significance Black spruce is the dominant tree species in boreal North America and has shaped forest flammability, carbon storage, and other landscape processes over the last several thousand years. However, climate warming and increases in wildfire activity may be undermining its ability to maintain dominance, shifting forests toward alternative forested and nonforested states. Using data from across North America, we evaluate whether loss of black spruce resilience is already widespread. Resilience was the most common outcome, but drier climatic conditions and more severe fires consistently undermine resilience, often resulting in complete regeneration failure. Although black spruce forests are currently moderately resilient, ongoing warming and drying may alter this trajectory, with large potential consequences for the functioning of this globally important biome.