Higher aboveground carbon stock in edge forests: a study at stand and tree levels in boreal and temperate forests.

On a global scale, human activities have significantly fragmented forest landscapes, resulting in over 20 % of the remaining forests being located within 100 meters of an edge. Forests adjacent to disturbances experience edge effects that can affect aboveground carbon storage through changes in forest structure. Our main objective was to assess how aboveground carbon stocks respond in edge forests over a large bioclimatic gradient of upland sites across the temperate and boreal forests of Eastern Canada, using powerline rights-of-way as a case study. We quantified the carbon stocks contained in living and dead trees of all sizes and measured dendrometric and growth variables at the stand and tree levels in forests adjacent to powerline rights-of-way. Compared with control forests (> 50 m from right-of-way), aboveground carbon stocks in edge forests (< 20 m) were up to 60 – 75 % higher in boreal spruce forests, 30 % higher in temperate forests, but only 2 % higher in boreal fir forests. Higher carbon stocks were linked to increased stand density, and thus a higher stand basal area, rather than larger tree diameters. Edge effect on tree characteristics (diameter, height, crown and height, and basal area increment) depended on the characteristics of the forest, with no clear pattern. No edge effect was found in a stand with a recently established right-of-way (less than three years), suggesting that the magnitude of the edge effect is dynamic over time. These estimates should improve the assessment of the carbon footprint of fragmented forest landscapes.