Forest Volume Relative to Cartographic Boundaries and Sample Spacing, Unit Size and Type

A 100-m-by-100-m (1 ha) square study area was established in the boreal forest of Quebec, Canada. The area was selected because of the presence of roughly equal amounts of three distinct forest types as identified from aerial photographs through subjective human interpretation. Within the study area, the position of every tree having a diameter breast height (dbh) of 9.1 cm and larger was determined in x- and y-coordinates. Sample units of various sizes and types were then established at a variety of spacings within the study area and the forest volume determined for each. A variety of analyses was conducted on each spacing/sample unit size and type combination to assess the nature of forest volume across cartographic boundaries. It was determined that at closer spacings and/or in using larger sample units, forest volume behaves as a continuum. However, the nature of the change in volume across forest stand boundaries was not (as was expected a priori) a gradual decrease in volume from a high volume stand to a low volume stand with relatively homogeneous areas further from the boundary. Instead it was found that, for a forest type boundary having stands of different densities but the same species on either side, the boundary was an area of relatively high volume with volume decreasing on both sides of the boundary as the distance from the boundary increased. Regardless of density, for a forest type boundary having stands of different species on either side, the boundary was an area of relatively low volume with volume increasing on either side of the boundary as the distance from the boundary increased. Readers are cautioned that these results were extracted from a single study site and that generalizing them to other forest conditions should only be done with care.