Abstract
Sustainable forest management requires information on the spatial distribution, composition, and structure of forests. However, jurisdictions with large tracts of noncommercial forest, such as the Northwest Territories (NWT) of Canada, often lack detailed forest information across their land base. The goal of the Multisource Vegetation Inventory (MVI) project was to create a large area forest inventory (FI) map that could support strategic forest management in the NWT using optical, radar, and light detection and ranging (LiDAR) satellite remote sensing anchored on limited field plots and airborne LiDAR data. A new landcover map based on Landsat imagery was the first step to stratify forestland into broad forest types. A modelling chain linking FI plots to airborne and spaceborne LiDAR was then developed to circumvent the scarcity of field data in the region. The developed models allowed the estimation of forest attributes in thousands of surrogate FI plots corresponding to spaceborne LiDAR footprints distributed across the project area. The surrogate plots were used as a reference dataset for estimating each forest attribute in each 30 m forest cell within the project area. The estimation was based on the k-nearest neighbour (k-NN) algorithm, where the selection of the four most similar surrogate FI plots to each cell was based on satellite, topographic, and climatic data. Wall-to-wall 30 m raster maps of broad forest type, stand height, crown closure, stand volume, total volume, aboveground biomass, and stand age were created for a ~400,000 km2 area, validated with independent data, and generalized into a polygon GIS layer resembling a traditional FI map. The MVI project showed that a reasonably accurate FI map for large, remote, predominantly non-inventoried boreal regions can be obtained at a low cost by combining limited field data with remote sensing data from multiple sources.
Highlights
A forest inventory (FI) provides information on the spatial distribution, composition, and structure of forest stands within a forested area [1,2]
How could a spatially contiguous FI be undertaken in a remote, northern boreal environment? Several studies have investigated the use of satellite remote sensing data for estimating and mapping forest stand attributes in limited areas of the Northwest Territories (NWT) [9,10,11,12], but applications anchored on local field data and covering a contiguous area at 30 m spatial resolution exceeding a single Landsat scene were notably absent in the 2000s
To circumvent the scarcity of field data, as proposed by Mahoney et al [8], thousands of surrogate FI plots scattered across the project area were created out of selected Geoscience Laser Altimeter (GLAS) footprints with forest attributes estimated using nested models based on ALS data (Section 3.3)
Summary
A forest inventory (FI) provides information on the spatial distribution, composition, and structure of forest stands within a forested area [1,2]. While digital photo-interpreted FIs are still routinely produced in Canada for forested areas under a government-regulated tenure agreement, the cost of such inventories (around CAD 1.30/ha) would be prohibitive over vast, inaccessible areas in northern boreal regions such as the NWT [8]. Given this context, how could a spatially contiguous FI be undertaken in a remote, northern boreal environment? How could a spatially contiguous FI be undertaken in a remote, northern boreal environment? Several studies have investigated the use of satellite remote sensing data for estimating and mapping forest stand attributes in limited areas of the NWT [9,10,11,12], but applications anchored on local field data and covering a contiguous area at 30 m spatial resolution exceeding a single Landsat scene were notably absent in the 2000s
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