Temporal analysis of forest structural condition at an acid mine site using multispectral digital camera imagery

Abstract

A large abandoned tailings deposit at a mine site near Timmins, Ontario, Canada has produced significant damage in an adjacent forest due to contamination and wind stress. Significant forest structure changes were measured between 1997 and 1999. A multivariate image-based forest structure index (FSI) was developed using canonical correlation analysis of 1997 field and airborne digital camera data. FSI included decreasing canopy closure and leaf area index, and increasing blown down and standing dead structure measures associated with image spectral, textural and radiometric fraction variables. An image model predicting FSI achieved an R ²=0.66. The model equation was then applied to 1999 airborne imagery to predict FSI for each plot. Comparing the 1999 image predicted FSI to that calculated from field data showed that the model was strong in predicting positive or no forest structure changes, but not increased structure degradation. The latter was due to the presence of herbaceous and shrub vegetation that had developed during the two-year period in open plots near the tailings where blow down was significant. The next research phase will derive means to separate these two signals in forests of open overstory.

Acknowledgments

The authors are grateful for funding and support of this research from the Natural Science and Engineering Council of Canada (NSERC), Ottawa, Canada and the US National Geographic Society, Washington DC. Field equipment was provided by the Department of Geography, Carleton University, Ontario, Canada and the Li-Cor instrument was supplied by the Canadian Centre of Remote Sensing (CCRS), Ottawa, Canada. Aircraft and personnel time for image acquisition were provided by AIRTEC, of Timmins, Ontario. Appreciation is extended to Chris Butson who aided in field data collection and acquired the airborne imagery and to Ian Olthof who collected the 1997 field data, developed the basis for the forest structure index methodology and provided a pre-submission review of this paper. Evan Seed provided photographs of tailings dust on leaves and bark in figure 3.