Edge effects increase soil respiration without altering soil carbon stocks in temperate broadleaf forests

Anthropogenic disturbance has left the world's forests highly fragmented, with a significant proportion of edge-affected area. Abiotic changes at forest edges are likely to affect forest soil carbon cycling, as higher temperatures and lower moisture availability in edge environments have well-documented effects on soil respiration. The present study sought to quantify persistent changes in soil carbon cycling in the fragmented broadleaf forests of southeastern Pennsylvania. At three sites with >80-year-old forest-field edges, three 100-m transects perpendicular to the edge were established. Monthly measurements of soil respiration, temperature, and moisture were made at fixed distances along each transect throughout the growing season. Soil carbon storage from 0 to 20 cm depth, litter biomass, and decomposition rates were also assessed. Soil respiration was significantly higher at forest edges, relative to the interior, and this effect penetrated 60 m into the forest. Significantly elevated surface soil temperature and decreased soil moisture were also observed in edge environments. Despite elevated soil respiration at the edge, soil carbon storage, litter biomass, and decomposition rates were invariant along edge to interior gradients. The temperature responsiveness of soil respiration was significantly higher in the forest interior (100 m), relative to locations <= 60 m from the edge. Edge effects altering elements of the soil carbon cycle were apparent in the forests of southeastern Pennsylvania, and principally manifest as increased soil respiration rates and decreased temperature responsiveness of soil respiration. Lack of variation in soil carbon pools and decomposition rates from the forest edge to interior suggests that increased soil respiration may be related to changes in root and rhizosphere respiration at the edge. These findings contribute to a growing body of evidence documenting increased soil respiration in the edge environments of temperate broadleaf forests. Discounting the alterations imposed by forest fragmentation on carbon cycling has the potential to produce misleading estimates of land-atmosphere CO2 exchange and terrestrial carbon storage.

Automated summary

Anthropogenic disturbance has caused forest fragmentation and modified the soil carbon cycling in forest edges, resulting in increased soil respiration rates, elevated soil temperature, and decreased soil moisture in edge environments. However, the study found that soil carbon storage and decomposition rates remained constant along the edge to interior gradients.