Assessing the Spatial Uncertainty of Boundaries on Forest Maps Using an Ecological Similarity Index

Forest stand boundaries are usually represented on vegetation maps as fine lines all having the same width. Thus spatial accuracy and precision are considered to be uniform over an entire map. However, real forest boundaries — i.e., those that can be observed on the ground— differ in degree of definition and contrast between adjacent stands. This study examines the association between ecological contrast and spatial context of forest boundaries and the uncertainty associated with their spatial reliability — i.e., location and probability of true existence. In this study, the contrast between adjacent forest stands was quantified via an ecological similarity index (ESI). The attributes used to estimate the value of this index for each mapped boundary were species composition, density class, height class and age class. In addition, the context, or neighbourhood, of each boundary was quantified by using the contrast values and their locations to calculate a local autocorrelation index (local Moran’s I). The relationships among the context, the contrast and the existence probability (consistency) were explored using discriminant analysis. (Consistency was measured by overlaying three multi-temporal forest maps and analyzing the result.) It was found that the consistency was most closely related to the contrast between the forest types present on either side of a forest stand boundary. Context was found to have no relationship to stand boundary consistency.