by Marie-Claude Boileau | 14 November 2022
Published in Remote Sensing of Environment, vol. 110, p. 488-500. https://doi.org/10.1016/j.rse.2006.05.025
We developed and tested a method for mapping aboveground forest biomass of black spruce (Picea mariana (Mill.) B.S.P.) stands in northern boreal forests of eastern Canada. The method uses QuickBird images and applies image-processing algorithms to extract tree shadow fraction (SF) as a predictive variable for estimating biomass. Three QuickBird images that were acquired over three test sites and 108 ground sample plots (GSP) were used to develop and test the method. SF was calculated using the tree shadow area over the area of a reference square overlain upon the images. Statistical tests demonstrated that local regressions for the three test sites were not statistically different. Consequently, a global regression was calculated with all GSP and produced R2, RMSE, and bias of 0.84, 14.2 t/ha and 4.2 t/ha, respectively. While generalization of these results to extended areas of the boreal forest would require further assessment, the SF method provided an efficient means for mapping biomass of black spruce stands for three test areas that are characteristic of the northern boreal forest of eastern Canada (Boreal and Taiga Shield Ecozones).
by Marie-Claude Boileau | 14 November 2022
Published in Forest Ecology and Management, 407: 84-94.
The most direct way of deciphering the dynamics of an ecosystem is by examining its biotic and abiotic components based on analysis of living and dead organisms distributed aboveground. The surface analysis method presented here provides a centennial to millennial stand-scale composition and disturbance history and is applicable in any wood-dominated ecosystem. A meticulous analysis of living and dead trees, and macro-remains (charcoal, leaves, insects) lying above mineral soil was performed in an untouched and in an anthropogenic sugar maple (Acer saccharum) forest. Sugar maple ecosystems provide an appropriate setting for testing this method as they are impacted by several natural and human disturbances. The living and dead components in both sites indicate an increase in species abundance independent of human interventions, although it was accelerated by logging in the anthropogenic forest. The stands were affected by recent insect outbreaks and by fire over the last 2000 years. Charcoal remains indicate that a mixed forest occupied both sites with sugar maple as a companion species for more than 1000 years. Surface analysis is a direct method for improving our understanding of current, past and future forest dynamics in natural and anthropogenic conditions, in this case highlighting how a foundational species of eastern North America thrives in different successional states and disturbance regimes. Novel tools that provide insight into pre-colonial ecosystems are greatly needed, given that a proper understanding of species current distributions and behaviour relative to allogenic disturbance is of crucial importance for restoration purposes and accurate prediction of future changes.
by Marie-Claude Boileau | 14 November 2022
Published in Forests: 8, 120.
Sugar maple (Acer saccharum) forests are among the main forest types of eastern North America. Sugar maple stands growing on Appalachian soils of the Lower St-Lawrence region are located at the northeastern limit of the northern hardwood forest zone. Given the biogeographical position of these forests at the edge of the boreal biome, we aimed to reconstruct the fire history and document the occurrence of temperate and boreal trees in sugar maple sites during the Holocene based on soil macro-charcoal analysis. Despite having experienced different numbers of fire events, the fire history of the maple sites was broadly similar, with two main periods of fire activity, i.e., early- to mid-Holocene and late-Holocene. A long fire-free interval of at least 3500 years separated the two periods from the mid-Holocene up until 2000 years ago. The maple sites differ with respect to fire frequency and synchronicity of the last millennia. According to the botanical composition of charcoal, forest vegetation remained relatively homogenous during the Holocene until recently. Conifer and broadleaf species coexisted in mixed forests during the Holocene, in phase with fire events promoting the regeneration of boreal and temperate tree assemblages including balsam fir (Abies balsamea) and sugar maple.
by Marie-Claude Boileau | 14 November 2022
Published in Forest Ecology and Management, 485: 118954.
The dynamics of the boreal forest have followed several successional trajectories during the Holocene caused by recurrent stand-scale, abiotic and biotic disturbances. Under stable environmental conditions, site disturbances should favour the regeneration of forest communities enabling the recovery process to produce forests similar to the pre-disturbance states. However, a failure in the post-disturbance recovery process can also occur to shift the forest communities to alternative states. Although fire is the main disturbance factor affecting the dynamics of the boreal forest, long-term resilience of most forest ecosystems remains poorly understood because of lack of stand-scale paleoecological evidence.
To evaluate the fire resilience of boreal forest ecosystems, we reconstructed their Holocene fire histories and documented their successional pathways at the stand-scale in two climatically contrasted regions (western continental versus eastern humid climates of boreal Québec, Canada) based on botanically identified and ¹⁴C-dated soil charcoal remains. Since the mid-Holocene, western closed-crown conifer forests were resilient to fire disturbance, but hardwood trees declined substantially. In the eastern region, closed-crown conifer forests were similar to those that are still observed today. In both regions, moderate fire frequency leads to recurrence dynamics that favour renewal of forest stands with the same composition. Yet, balsam fir–paper birch stands follow a successional pattern characterized by the establishment of paper birch, with subsequent increasing abundance of balsam fir. This allows the maintenance of forests composed of these species, the dominance of which fluctuates according to the time elapsed since the last fire. The succession from black spruce to balsam fir stands seems to be an uncommon process that requires a prolonged fire-free period. Although most closed-crown forests are resilient post-fire ecosystems that have persisted over several millennia, their resilience is precarious as evidenced by the transformation of some forests into lichen woodlands after fire.
by Marie-Claude Boileau | 11 November 2022
Published in Canadian Journal of Forest Research, 46: 822-831.
In the St-Lawrence Lowlands, sugar maple (Acer saccharum Marsh.) is considered the dominant species of old-growth deciduous forests, whereas red maple (Acer rubrum L.) tends to dominate sites recently disturbed by logging and agricultural practices. Considering that the long-term influence of fire is not documented for such stands, we reconstructed the postglacial tree composition (as deduced from charcoal species) and fire history of a sugar maple stand (Ste-Françoise area) and a red maple stand (Villeroy area) located southwest of Québec City, Canada. The sites are 10 km apart and show contrasting soil and landform features. Using botanical identification and 14C dating of soil macro-charcoal, we found that fire struck both maple stands 14–20 times since deglaciation. Most fires occurred in the early Holocene and over the last 2000 years, with the mid Holocene being a period with low fire frequency or no fires. During the last 1600 years, the Villeroy stand shifted from a Tsuga canadensis (L.) Carrière – conifer forest to a mixed forest and, most recently, to a red maple stand as fire became more frequent, possibly due to human activities over the last 400 years. This study confirms the influence of fire on the development of maple forests. Fire should be considered as an important disturbance factor in the dynamics of temperate deciduous and mixed forests.
