The impacts of forest harvesting will interact with a changing climate in complex ways. Forest soils, following tree harvest, are susceptible to carbon (C) and nitrogen (N) losses owing to increased mineralization and decreased inputs from vegetation. Climate models predict increases in temperature, as well as changes in precipitation in the northeastern United States. Increases in soil temperature and moisture alone, separate from harvesting effects, have been shown to increase C and N mineralization. Therefore, predicted regional climate change may exacerbate post-harvest C and N losses in some areas such as northeastern forests. A post-harvest climate manipulation experiment was established in the ridge and valley region of central Pennsylvania. The experimental design included 4 treatments: heated, irrigated, heated+irrigated, and ambient. Heated treatments increased surface temperatures by 1.5 °C and 3.0 °C for day and night respectively. Irrigated plots received +20% of long-term average precipitation. Our objectives were to 1) quantify changes in soil C and N pools and fluxes due to increased temperature and precipitation treatments in a post-harvest forest and 2) understand how changes in C and N cycling are linked to changes in soil microbial community composition and enzyme activity.
Results/Conclusions
Average annual increase in soil temperature was 2.85 °C at 5 cm depth. After two years of treatment soil respiration rates were significantly lower in the heated+irrigated plots and higher in heated plots. Heating decreased soil respiration sensitivity to temperature (Q10). Heating also increased available N within the first year, but the effect was diminished in the second year. Irrigation alone shows no significant effect on soil respiration. However, irrigation has slightly, but significantly, increased the percentage of labile C per g total C. The soil microbial community was assessed via community level physiological profile using 15 substrates. Both treatments appear to affect the microbial communities' response to specific substrates. These preliminary results suggest that heating, but not increased precipitation, increases soil C and N mineralization in harvested forest soils; responses that may increase post-harvest soil C and N losses in a warmer climate.
