Higher aboveground carbon stocks at forest edges

On a global scale, human activities have significantly fragmented forest landscapes, resulting in over 20% of the remaining forests being located within 100 m 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 aboveground carbon stocks and their drivers at forest edges across a large bioclimatic gradient of upland sites in the temperate and boreal forests of Eastern Canada, using powerline rights-of-way as a case study. We quantified carbon stocks in living and dead trees of all sizes and measured tree growth at stand and tree levels in forests adjacent to powerline rights-of-way. Compared with reference forests (> 50 m from right-of-way), aboveground carbon stocks at forest edges (< 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 effects on tree characteristics (diameter, total height, crown length and area, and basal area increment) showed no clear pattern and depended on the characteristics of the forest. 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 varies over time. This study will improve the assessment of the carbon footprint of fragmented forest landscapes. • We studied edge effects at both the tree and stand levels in boreal and temperate forests. • Edge effect enhanced aboveground carbon stocks by 2–75%. • Increased carbon stocks were associated with higher stand density, rather than larger tree diameter. • Basal area increment showed no increase after right-of-way clearing.