Decomposition varies spatially and temporally by vegetation cover and elevation in a West Virginia watershed

Background/Question/Methods

Microclimate effects on decomposition, as a function of forest structure and/or elevation gradients within local scales, remain a relatively unexplored and potentially crucial area of research given the high uncertainties surrounding the spatial and temporal variation in decomposition rates from empirical studies. To assess the influence and interaction of forest structure and elevation on decomposition, we conducted a two-year litter bag study from 2011 to 2013 using a common leaf litter (Betuala allgehaniensis) in the Weimer Run watershed (373 ha) near Davis, WV. We used a factorial design and descritized the watershed into three vegetation classes (OPEN – an open gap within the forest; CANOPY – beneath the forest canopy; SHRUB – beneath the shrub layer within in the forest) within three elevation classes (LOW - 975 m; MID - 1050 m; HIGH 1100 m). Litter bags were placed on the soil surface within plots at each combination of vegetation and elevation class (i.e. LOW OPEN, HIGH CANOPY, etc.). There were three replicates of each combination for a total of 27 plots (3 vegetation classes x 3 elevation classes x 3 replicates). Concurrently, lignin and cellulose standards were also deployed in the same manner and retrieved at the same schedule as the litter bags (1, 6, 12, 18, and 24 months). One series of lignin and cellulose standards were placed on the soil surface, while another series were buried at a depth of 5 cm. Both litter and standards were analyzed for mass loss, rates of decomposition, and changes in cellulose and lignin concentrations over time. 

Research Questions

1) Are the effects of vegetation cover on decomposition within and across an elevation gradient within a cool, moist watershed significant?
2) Does augmenting litter bag experiments with additional, separate common lignin and cellulose sources better estimate landscape controls on decomposition?

Results/Conclusions

Total mass loss from litter bags differed with elevation after two years (LOW 41.1%, MID 44.4%, and HIGH 47.8%). Beneath vegetation classes, OPEN sites showed the highest total mass loss (41.7%), followed by CANOPY sites (44.2%), and SHRUB sites (47.7%). Relative decomposition rates (k) and total mass loss (%) among elevations were influenced strongly by season, with significant differences among elevation classes after the one month (p = 0.0200) and 12 months (p =0.0201). While further analysis is warranted, initial findings indicate possible interactions across these environmental gradients.