Monday, August 2, 2010 - 1:30 PM

COS 6-1: Interannual variability of soil respiration in managed forests in Ozarks, Missouri

Jianye Xu, University of Toledo

Background/Question/Methods

The variability of soil respiration (RS) and its regulatory factors, e.g., soil temperature (TS) and soil moisture (MS) were investigated over five years in similar Ozark managed forests. The instruments used in for the measurements includes: EGM-4(RGA, EGM-4 Environmental Gas Monitor, PPsystems, UK) for RS and TDR-100 for MS ( Campbell Scientific Inc., Logan, UT). The Missouri Ozarks Forest Ecosystem Project (MOFEP) has three forest treatments including: control no-harvest (NHM), even-aged clear-cut harvest (EAM), and uneven-aged single-tree harvest (UAM).

Results/Conclusions

Our results showed that: seasonally, RS shared a similar trend with TS; interannually, total summer precipitation (defined from May-August) (PPTS) was highly related to summer mean RS in the EAM and UAM. The five-year measurements of RS showed more fluctuations at EAM and UAM than at NHM. Overall, RS was higher in wet years and lower in dry years in harvested treatments, although these differences were statistically significant only in 2007 when the area experienced a severe summer drought. The lower interannual variability in RS at NHM suggested that NHM was more resistant to natural disturbance than the harvest treatments. The NDVI of the measured plots supports this conclusion too. There existed thresholds in the relationship between TS and RS (~23°C) over the five-year period for all the treatments. Based on minor changes in MS, the TS threshold changed monthly from May to August, with the lowest threshold in May (~19°C) and the highest in July (~25°C). The threshold also ranges from the lowest (~20°C) occurring in 2007 and the highest (~25°C) in 2008 annually. The low MS and depleted substrate supply at high TS is reasoned for the TS thresholds.