Canadian Forest Service Publications
Tracking forest attributes across Canada between 2001 and 2011 using a k nearest neighbors mapping approach applied to MODIS imagery. 2018. Beaudoin, A.; Bernier, P.Y.; Villemaire, P.; Guindon, L.; Jing Guo, X. Can. J. For. Res. 48: 85-93.
Available from: Laurentian Forestry Centre
Catalog ID: 38979
CFS Availability: PDF (request by e-mail)
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Mapping Canada’s forests is a significant challenge given their extent and the interprovincial differences in forest inventories. We created new sets of nationally consistent forest attribute maps for the years 2001 and 2011 by building upon previously published work with the objective to determine if sequential maps of forest attributes could be used to quantify changes over time. We first refined our previously published methodology of using the k nearest neighbors (kNN) prediction method and MODIS spectral reflectance data as predictive variables. The maps were generated using an improved reference dataset and a new analytical kNN workflow. We then evaluated 2001 to 2011 changes in two key attributes, aboveground biomass and percent tree cover, on pixels identified from published sources as having undergone fire, harvest, or postdisturbance regrowth during that period. For all three change types, average changes in both aboveground biomass and percent tree cover between 2001 and 2011 matched expectations relative to the dynamics of Canadian forests. Our results support the use of sequential national maps of forest attributes for evaluating regionally aggregated disturbance-related changes in forest properties. The new forest attribute maps are available from Beaudoin et al. (2017; doi:10.23687/ec9e2659-1c29-4ddb-87a2-6aced147a990) at http://ouvert.canada.ca/data/fr/dataset/ec9e2659-1c29-4ddb-87a2-6aced147a990.
Plain Language Summary
This work helped create new Canada-wide forest attribute maps for 2001 to 2011, at a resolution of 250 m, using MODIS satellite data and photo plots from the National Forest Inventory (NFI). These maps were created by refining the 2001 forest attribute maps and updating them for 2011. To achieve this, the researchers obtained more accurate estimates of forest attributes through an improved reference dataset based on the NFI. They also used an optimized kNN (k-nearest neighbours) statistical method to generate the maps.
Using these maps, they were then able to estimate and map changes for two key forest attributes, i.e. aboveground biomass and the percentage of tree cover, between 2001 and 2011 across Canada. These changes were assessed during this period based on major disturbances (fire, cutting) and regeneration. These new reference maps can be used at the regional and national levels for a wide variety of applications, such as monitoring forest attribute changes and modelling the future state of forests under the effects of climate change.
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