by Marie-Claude Boileau | 14 November 2022
Published in Forest Ecology and Management, vol. 266, p. 66-74.
This study demonstrates a method for mapping forest stand polygons based on four forest attributes (volume, basal area, height, and crown closure) using shadow fraction values that were estimated from high spatial resolution QuickBird panchromatic images. The method was tested over three test sites in northeastern Canada that were largely dominated by black spruce (Picea mariana (Mill.) BSP). The method involved four sets of procedures: (i) estimating shadow fraction from the panchromatic band of QuickBird images; (ii) generating site-specific and global regression models linking shadow fraction with each of the four forest attributes; (iii) mapping the forest attributes as a grid layer (30 × 30 m) for each test site using the global regression models; and (iv) generating stand polygons from the raster layers. Between 2002 and 2004, 108 ground sample plots were acquired to develop local regression models.
Stand volume maps were produced using both the shadow fraction method and conventional forest stand maps (derived from aerial photo-interpretation) for a test site. Volume patterns were similar, and total volume for the test site differed by only 5.6% between the two maps. Lastly, the raster images derived from the shadow fraction method were used to produce a stand map following guidelines similar to those used by provincial inventory. In all cases, our results suggest that the shadow fraction method is a reliable and convenient way to map forest stand polygons and related attributes of black spruce stands in northeastern Canada.
by Marie-Claude Boileau | 14 November 2022
Published in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 8(11), 5199-5211.
Boreal forests have a significant impact on the Earth’s climate and on global warming. In this context, a large-scale mapping method was developed to characterize forest attributes, surficial deposits and forest disturbance history in the absence of support datasets. The method, which was based on remote sensing data, image processing techniques and image interpretation, was applied over a very large area (680 000 km2) of Québec (Canada) that was dominated by black spruce (Picea mariana [Miller] BSP). The method involved five steps: 1) mapping the vegetation based on unsupervised classification, imputation and segmentation methods; 2) mapping the history of fires that occurred over the mapping area based on archive Landsat images; 3) determining the dominant species characterizing forest stands; 4) mapping surficial deposits; and 5) assessing accuracy of map attributes based on video datasets. Kappa values ranged from 72.5% to 96.3%. The results demonstrated that our method is a convenient and inexpensive way of mapping forest ecosystems over large areas of the northern boreal forest.
by Marie-Claude Boileau | 14 November 2022
Published in Botany 96: 411-423 https://doi.org/10.1139/cjb-2018-0016
The long-standing hypothesis that sugar maple (Acer saccharum Marshall) communities are maintained at equilibrium by present climate and small-scale disturbances is questioned because empirical evidence is accumulating about the ability of the species to withstand several stand-scale disturbances. The fire history of a sugar maple site at the northeastern range limit of the species (Gaspe Peninsula, eastern Canada) was documented to test the hypothesis that this forest type is resilient to fire disturbance. The fire history was reconstructed using radiocarbon-dated soil macro-charcoals. Two main fire periods were recorded during the Holocene. The oldest period occurred between 9055 and 8265 cal. years BP, and was characterized by the presence of conifers, including spruce. After 6900 years of fire-free activities, the second period covered the last 1335 years, and was characterized by the presence of sugar maple in the charcoal assemblage. The dominance of sugar maple after more than 1000 years of recurrent fires underlines the species resilience to frequent site disturbances. The soil of the forest stand was heavily disturbed by earthworms. However, the dense seedling and sapling bank of sugar maple suggests that earthworms do not adversely affect the regeneration and survival of the species.
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.
