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 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.