Soil respiration in a longleaf pine chronosequence

Background/Question/Methods

Soil respiration is the largest flux of carbon dioxide from ecosystems and controls whether forests are carbon sinks or sources. Little is known about soil respiration in longleaf pine forests (Pinus palustrisMill.), which are being restored throughout the southeastern United States, or how our understanding of carbon dynamics in other pine forests applies to longleaf pine ecosystems. The goals of this study, currently in progress at Fort Benning in Columbus, Georgia, are to: test a soil respiration model based on southern Alabama longleaf pine forests; enhance the understanding of how environmental conditions affect variation in soil respiration; and determine if these patterns change with stand development and stand structure. Soil respiration, temperature, and moisture, buried coarse woody debris, root and litter biomass, distance to adjacent trees, phenology, and vegetative ground cover are being measured monthly for two years in longleaf pine stands aged 5, 12, 21, and 87 years old. Soil temperature is being measured continuously in order to develop annual estimates of soil respiration.

Results/Conclusions

Soil respiration followed seasonal trends in soil temperature, which accounted for the majority of variation in soil respiration across and within stand ages. Other factors significantly related to soil respiration including distance to nearest tree and soil moisture, although relationships varied among stands. During periods of non-limiting soil moisture, soil respiration can be adequately predicted using the exponential soil temperature model (Rs = 0.4723*e^(0.0995T), where Rs is soil respiration and T is soil temperature). A more complex model that takes into account soil moisture, distance to neighboring trees, and stand age in addition to soil temperature increased the fit and provided the best fit across the dataset (R²=0.62). Additional work will focus on the contributions of root and microbial respiration to soil respiration and their responses to environmental factors. Results from this study demonstrate the importance of stand age and forest structure in addition to soil temperature when modeling carbon dynamics at local and regional scales.