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 fixede distances along each transect throughout the growing season. Soil carbon storage from 0-20 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 bssomass, 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.

Soil respiration (average of three measurements made with a LI-6400), soil temperature (5 and 10 cm depth), and soil moisture data were collected monthly from May to October 2018 at three fragmented forest edges in southeastern Pennsylvania. Measurements were collected at three transects per site at distances of 5, 15, 30, 60, and 100 m from the edge. Decomposition of a common substrate (cellulose filter paper) was also measured over this time period. Additional samples were collected from each measurement location in June 2018 to determine soil carbon and nitrogen storage at 0-10 and 10-20 cm depth (using elemental analysis of soil carbon and nitrogen together with soil bulk density), as well as litter layer (O horizon) biomass.

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