Luc Guindon

Pixel-Based Image Compositing for Large-Area Dense Time Series Applications and Science

Abstract Free and open access to the more than 40 years of data captured in the Landsat archive, combined with improvements in standardized image products and increasing computer processing and storage capabilities, have enabled the production of large-area, cloud-free, surface reflectance pixel-based image composites. Best-available-pixel (BAP) composites represent a new paradigm in remote sensing that is no longer reliant on scene-based analysis. A time series of these BAP image composites affords novel opportunities to generate information products characterizing land cover, land cover change, and forest structural attributes in a manner that is dynamic, transparent, systematic, repeatable, and spatially exhaustive. Herein, we articulate the information needs associated with forest ecosystem science and monitoring in a Canadian context, and indicate how these new image compositing approaches and subsequent derived products can enable us to address these needs. We highlight some of the issues and opportunities associated with an image compositing approach and demonstrate annual composite products at a national-scale for a single year, with more detailed analyses for two prototype areas using 15 years of Landsat data. Recommendations concerning how to best link compositing decisions to the desired use of the composite (and the information need) are presented, along with future research directions. Résumé L’accès libre et gratuit à plus de 40 ans de données dans l’archive Landsat combiné à l’amélioration des produits d’imagerie standardisés et l’augmentation des capacités de traitement et de stockage informatiques ont permis la production d’images composites basées sur les pixels de réflectance de surface de grande superficie sans nuages. Les composites du « meilleur pixel disponible » (best-available-pixel; BAP) représentent un nouveau paradigme en matière de télédétection qui ne dépend plus de l’analyse par scène. Une série chronologique de ces images composites BAP offre de nouvelles occasions de générer des produits d’information qui caractérisent la couverture terrestre, le changement de la couverture terrestre et les attributs structurels de la forêt d’une manière dynamique, transparente, systématique, répétable et spatialement exhaustive. Ici, nous articulons les besoins d’information liés à la science et à la surveillance des écosystèmes forestiers dans un contexte canadien, et nous indiquons comment ces nouvelles approches de composition d’image et les produits qui en découlent peuvent nous permettre de répondre à ces besoins. Nous soulignons quelques-uns des problèmes et des possibilités associés à une approche de composition d’image et nous démontrons des produits composites annuels à l’échelle nationale pour une année, avec des analyses plus détaillées pour deux zones prototypes utilisant 15 ans de données Landsat. Des recommandations concernant la meilleure façon de lier des décisions de composition d’images à l’utilisation souhaitée du composite (et le besoin d’information) ainsi que les orientations futures de la recherche sont présentées.

Climate change impacts on forest landscapes along the Canadian southern boreal forest transition zone

ContextForest landscapes at the southern boreal forest transition zone are likely to undergo great alterations due to projected changes in regional climate.ObjectivesWe projected changes in forest landscapes resulting from four climate scenarios (baseline, RCP 2.6, RCP 4.5 and RCP 8.5), by simulating changes in tree growth and disturbances at the southern edge of Canada’s boreal zone.MethodsProjections were performed for four regions located on an east–west gradient using a forest landscape model (LANDIS-II) parameterized using a forest patch model (PICUS).ResultsClimate-induced changes in the competitiveness of dominant tree species due to changes in potential growth, and substantial intensification of the fire regime, appear likely to combine in driving major changes in boreal forest landscapes. Resulting cumulative impacts on forest ecosystems would be manifold but key changes would include (i) a strong decrease in the biomass of the dominant boreal species, especially mid- to late-successional conifers; (ii) increases in abundance of some temperate species able to colonize disturbed areas in a warmer climate; (iii) increases in the proportions of pioneer and fire-adapted species in these landscapes and (iv) an overall decrease in productivity and total biomass. The greatest changes would occur under the RCP 8.5 radiative forcing scenario, but some impacts can be expected even with RCP 2.6.ConclusionsWestern boreal forests, i.e., those bordering the prairies, are the most vulnerable because of a lack of species adapted to warmer climates and major increases in areas burned. Conservation and forest management planning within the southern boreal transition zone should consider both disturbance- and climate-induced changes in forest communities.

A strategy for mapping Canada's Forest biomass with Landsat TM imagery

Estimates of forest biomass are needed to meet Canadas international reporting requirements and to provide important inputs for global change, carbon accounting, and forest productivity models. The Canadian Forest Service, in cooperation with the Canadian Space Agency, has developed a strategy for mapping Canadas forest biomass as part of the Earth Observation for Sustainable Development of Forests (EOSD) Project. The strategy includes: (i) development of a biomass mapping method, (ii) regional expansion of the method, and (iii) national implementation. The method estimates forest biomass at the forest management stand level using forest cover type and structure information extracted from Landsat Thematic Mapper (TM) data. Regional expansion of the method has occurred over several pilot regions that represent a range of forest ecosystems across Canada. Validation of regional products provides an indication of the precision of the method, defines the data requirements and limits to regional expansion, and has led to the development of research themes. Specific research themes address known limitations of the method by (i) improving the extraction of cover type and structure information from satellite imagery, (ii) defining the role of environmental variables and other factors for biomass estimation, and (iii) separating understorey and overstorey biomass.

Modeling and mapping forest biomass using forest inventory and Landsat TM data: results from the Foothills Model Forest, Alberta

Forest biomass information is needed for reporting of selected indicators of sustainable forest management and for models that estimate carbon budgets and forest productivity, particularly within the context of a changing climate. In collaboration with the Canadian Space Agency, a strategy for mapping Canadas forest biomass has been developed as part of the Earth Observation for Sustainable Development of Forests (EOSD) project. This paper reports on the results derived from an application of this strategy to a pilot study area in the Foothills Model Forest, Alberta. Methods to estimate forest biomass have been developed using tree-level inventory plot data that is then extrapolated to the stand level by statistical relationships between biomass density and stand structural characteristics. These ground-based biomass estimates serve as source data that are related to stand structure derived from classified Landsat TM data. Models developed from inventory data to estimate biomass density attained adjusted R/sup 2/ values that ranged from 0.60 to 0.77 for 5 species groups, and tests with an independent validation sample compared favourably for all species (deciduous, lodgepole pine, mixed species, white spruce/fir), except black spruce/larch. Landsat-derived forest biomass was statistically and moderately correlated to the inventory-derived biomass with values of 0.63, 0.68, and 0.70 for conifer, deciduous, and mixed species, respectively. Research areas were identified from both inventory and remote sensing perspectives that will lead to incremental improvements in biomass estimation.

Assessing the potential of the differenced Normalized Burn Ratio (dNBR) for estimating burn severity in eastern Canadian boreal forests

There is considerable variation in the degree of burn severity in boreal fires. One approach that has been used to capture this variation from field and remote sensing perspectives for western Canadian boreal forests is the Composite Burn Index (CBI) and differenced Normalized Burn Ratio (dNBR). Of interest was how well these methods may perform for fires in eastern Canada. This study investigated the CBI-dNBR relationship for selected fires in the eastern boreal forests of Canada, with a view towards contributing to the generalisation of a Canada-wide model. Results for the sampled region showed no difference in the CBI-dNBR relationship between black spruce- and jack pine-dominated stands, whereas this relationship was best described by a Generalised Additive Model (GAM). The dNBR-derived maps would also be useful in support of research and post-fire management in burns outside the studied territory and time frame covered by the existing burn severity mapping system already used in this region. The Saturated growth model proposed for the western boreal region also performed well for our eastern boreal region, thus further supporting the development of a national model.

Approaches for forest biomass estimation and mapping in canada

Knowledge of forest biomass is necessary for reporting on the state of Canadas forests. It is also an indicator of carbon that enables insights on the interaction between forests and the atmosphere. Forest biomass information has largely been aspatial and derived using plot estimates from Canadas National Forest Inventory. Provincial and territorial governments and private industrial organizations have broadened the diversity of information needs and demand for methods that are more spatially explicit. These realities have resulted in a variety of data sources nested within four approaches that can be applied from local to national scales. Earth observation data contribute to each of these approaches to varying degrees and not all approaches result in large area biomass maps. This paper describes the approaches for biomass mapping in Canada, their synergism, and highlights their dynamic nature as new data sources and ongoing developments will continue to refine these approaches to estimate, map, and monitor forest biomass in Canada.

Mapping forest biomass on several pilot regions in Canada with Landsat TM and forest inventory data

A method has been developed to map forest biomass with Landsat TM and ETM imagery coupled with forest inventory data. The method involves applying an unsupervised classification to a Landsat TM/ETM scene. The unsupervised clusters are labelled according to cover types and forest structure (crown closure and height) using random samples extracted from Inventory datasets as training pixels. Biomass values are assigned to the clusters according to the dominant forest type and structure contained within the clusters. The method was tested on five pilot regions throughout Canada with an objective of evaluating its application in several ecological regions with different species composition and stand structure. This paper concerns (1) the implementation of this method and (2) the comparison of those results between regions. The overall results for classifying forest cover types range from 50 to 60% for the five regions. Correlations between remotely sensed and inventory biomass estimates are variable for different species and pilot regions. However, results show that the method provides a complement to existing inventory-based methods for mapping biomass in managed areas and may constitute an alternative approach for northern areas with weak forest inventory databases.

Chapter 3 – Quantifying Forest Biomass Mobilisation Potential in the Boreal and Temperate Biomes

Using common methodology and data sources, two indicators were derived to estimate the levels of forest biomass production achieved today for 12 countries in the boreal and temperate biomes and to inform on the potential availability of forest bioenergy feedstocks. The first indicator was used to evaluate the intensity of roundwood production per unit of forest net primary production (NPP). The second indicator was used to estimate the degree of bioenergy production per unit of roundwood production. The values of these indicators were used to demonstrate whether forest biomass mobilisation could be achieved via intensification of forest management activities, in which forestry would appropriate a larger share of forest ecosystem NPP and/or intensification of biomass recovery from silvicultural, harvesting and wood processing operations, in which bioenergy would appropriate a larger share of forest by-products/residues. The indicator values varied widely among countries, demonstrating that mobilisation of forest biomass is relatively high in some countries (eg Belgium, Germany), while significant gains could be achieved in others (eg Canada, Russia). The feasibility of enhancing the availability of feedstocks for bioenergy production from the forest depends on environmental, social, economic and technological constraints at the national and/or regional level.