Quantifying the Impacts of Nova Scotia Forest Management Practices on Forest Stand Albedo and Surface Temperatures

Abstract

In an effort to mitigate climate change, the Canadian government has increased focus on natural carbon sequestration through afforestation (i.e., the planting of forests where there were previously no forests) and reforestation (i.e., the planting of forests to replace a forest than was removed or disturbed). Traditionally, these forest management practices have preferred coniferous (softwood) tree species, which has led to wide scale species conversion across Europe and North America, increasing coniferous forest cover. Recent studies have linked these forestation practices to increased surface temperatures in managed forests. Coniferous forests have lower albedo than deciduous forests, absorbing a greater ratio of solar energy, which is re-emitted as heat and raises surrounding temperatures. This thesis tested the hypothesis that forest management practices in Nova Scotia increase coniferous tree cover, which in turn reduces canopy albedo and raises surface temperatures. Remote sensing methods were used to test the relationship between forest treatments and stand biophysical characteristics. Albedo, surface temperature, and Normalized Difference Water Index outputs for Nova Scotia were derived from multispectral and thermal satellite imagery collected by Landsat 8 over July and August 2022. Forest stand data shared by the Nova Scotia department of Natural Resources and Renewables identify 216,235 forest stands, classified into two groups: 89,171 treated forest stands, and 127,064 natural forest stands. Analysis successfully demonstrated relationships between forest management practices and forest stand biophysical characteristics using remote sensing derived measurements. Contradicting the original hypothesis, treated stands exhibited higher mean albedo than natural stands, a process partially explained by the scarce canopy cover of young replanted forests. Further, mean surface temperatures in treated stands were 0.4-1.2 °C warmer than comparable natural stands. This relationship indicates current forestry policies may, in fact, be increased surface temperatures in managed forests. While further discriminant analyses failed to meet confidence thresholds, classification accuracies of ~70% suggest some discriminant ability within the predictor variables (albedo, surface temperature, and NDWI). The overall results of this thesis indicated that forest management is creating higher forest surface temperatures, but this phenomena is not related to decreased albedo in treated stands, and is likely caused by underlying processes not addressed in this study. The outcomes of this work call into question the efficacy and validity of using forests as climate change mitigators. Specifically, whether Canada should continue to implement climate change policies that promote reforestation and afforestation if these methods may warm surface temperatures. In-depth analysis assessing the value forestation as a climate mitigation strategy should be conducting; contrasting the cost of increased surface temperatures caused by forest management against the considerable carbon sequestration ability of forests.