Soil respiration response to experimental disturbances over 3 years

Soil respiration is a major pathway for carbon cycling in terrestrial ecosystems yet little is known about its response to natural and\ud anthropogenic disturbances. This study examined soil respiration response to prescribed burning and thinning treatments in an old-growth, mixedconifer\ud forest on the western slope of the Sierra Nevada Mountains. Experimental treatments were applied in 2001 using a full factorial design\ud consisting of two levels of burning and three levels of thinning, and included: unburned–unthinned (UN), unburned–overstory thinned (US),\ud unburned–understory thinned (UC), burned–unthinned (BN), burned–understory thinned (BC), and burned–overstory thinned (BS).We measured\ud soil respiration rate (SRR), soil moisture (MS), soil temperature (TS), and litter depth (LD) for three replicates of each of three dominant patch types\ud (closed canopy, open canopy, and ceanothus shrub) within each of the six treatments (n = 54). The same sampling points were measured from May\ud to August in 2000 (pre-treatment) and in 2002, 2003, and 2004 (post-treatment). Within our sampling period there was as much as 37% variation\ud ( p = 0.0005) between years in the undisturbed patches, which appeared to be driven by changes in precipitation. SRR also varied by year in all\ud treated plots (US: p = 0.0516; UC: p = 0.0006; BN: p = 0.0158; and BC: p = 0.0040), with the exception of BS ( p = 0.3344). SRR response to\ud disturbance varied with patch type, year, and treatment type. In most cases, burning and the combination of burning and thinning had less of an\ud effect on mean SRR than thinning alone. Ceanothus patches appear to have recovered fastest, while treatment effects remained 3 years after\ud thinning in closed canopy ( p = 0.0483 and 0.0333 in UC and US, respectively) and open canopy patches ( p = 0.0191 in US). Open canopy patches\ud showed no response to any treatment aside from US. Both UC and US increased SRR in closed canopy and ceanothus patches, and US decreased\ud SRR in open canopy patches. BS increased SRR in 2004 in closed canopy patches ( p = 0.0108), but no significant changes occurred in any patch\ud type in response to BN or BC treatments. Across all treatments, the relationship of SRR with temperature, moisture, and litter depth changed in\ud post-disturbance years. The results of this study can be used to help understand how management of Sierran mixed-conifer forests affects soil\ud carbon sequestration