The magnitude and causes of edge effects on soil organic carbon stocks within and across urban to rural forest patches

Abstract

Landscape fragmentation has created large areas of forest edge. Understanding how soil organic carbon (SOC) stocks within forest edges respond to fragmentation is essential to assess carbon budgets; however, the causes and magnitude of edge effects on SOC stocks have been poorly characterized. Here, we quantify the edge effects on SOC stocks within and across urban to rural forest patches from three fragmented urban forests to a large patch of rural forest. The SOC stocks within 20 m of the rural forest edge (1.86 kgC m(-2)) is on average 80% lower than the interiors of rural forest (10.47 kgC m(-2)). We found that biotic factors, including annual litterfall mass (R-2 > 0.94), peak leaf area index (R-2 > 0.92), and fine-root mass density (R-2 > 0.77), explained the spatial variation in SOC stocks within the rural forest. In urban forests, human activities at forest edges led to contrasting edge effects on SOC stocks, for instance, the SOC stocks at the east edges (4.74 kgC m(-2)) were 56% greater than at the west edges (3.03 kgC m(-2)) explained by the adjacent land uses (e.g., paved roads vs. non-paved soils) and in-situ litterfall management. We also found significant differences in summer soil temperature (Delta T-S > 2.8 degrees C) and soil moisture (Delta VWC > 0.05 m(3) m(-3)) between the east and west forest edges. Our results reveal that the factors responsible for the edge effects on SOC stocks in rural forests are biotic factors, while heterogeneous human activities at the local scale lead to complex edge effects on urban forest SOC stocks.