Study site: Our study site was within two age-since-disturbance chronosequences as well as three end-member climax communities at the University of Michigan Biological Station. A chronosequence of stand age and disturbance history was created in four, 1 ha contiguous stands which were experimentally clear-cut and burned in 1936, 1954, 1980, and 1998. Our second chronosequence consisted of plots that were cut but not burned in 1911, 1952, 1972, and 1987. All stands in both chronosequence experienced and initial cut and burn disturbance in 1911, therefore one sequence experienced 2 burn disturbances, while the other sequence experienced only 1 burn disturbance. The uniform disturbance history of these stands, together with their common original vegetation, soils, slope, and climate afforded us the opportunity to investigate forest C storage over time. The study site lies on a gently sloping high outwash plain with well drained spodosolic soils (92.9% sand, 6.5% silt, 0.6% clay, pH 4.8) derived from glacial drift and classified as entic haplorthods. The three end-member study sites consisted of a mixed deciduous-conifer 184 year old stand (CP), and two conifer dominated 124 year old stands (BS40, BS42).
Methods: We measured soil respiration in 29 plots within these 11 experimental stands using a LI-COR LI-6400 and a LI-6400-09 soil CO2 flux chamber. Five soil collars constructed from polyvinyl chloride (PVC) pipe were installed randomly within each plot (145 collars total). The center of each 0.1ha plot was determined and collars were placed radially at 0°, 70°, 140°, 210°, and 280° and 3, 6, 9, 12, and 15 meters respectively. Respiration within collars was measured 7 times throughout 4 weeks in July-August 2014. At each measurement station thermocouples were inserted at 0.075 m into the soil, and one 0.30 m time domain reflectometry (TDR) probe was used to measure soil water content. Point measurements of soil temperature (Ts) and volumetric soil water content (θv) were recorded immediately following respiration measurements.