Forest ecosystems perform vital functions including storing carbon, the cycling of critical nutrients and fostering biodiversity, and many of these functions can be reduced after disturbance. Most research into the impacts of disturbance on forest health investigate single disturbances, far fewer interrogate the interactive effects of several disturbances. Here, we investigated the interactive effects of three common disturbances experienced by temperate forests across the eastern U.S., namely canopy gaps (e.g., from severe weather events), surface fire, and grazing by large herbivores (i.e., deer), on soil carbon content and bacterial and fungal abundance in a long-term forest disturbance experiment in the Monongahela National Forest, WV. Previous research into aboveground responses to the interactive effect of the aforementioned disturbances determined that canopy gaps and fire promoted a more diverse canopy and herbaceous layer, but only when herbivores were excluded. However, it remains unknown whether these above-ground changes can have below-ground consequences. To determine this, we used an established long-term field experiment that implements three eastern forest disturbances (canopy gaps, surface fire and herbivory), as well as the interactions between them. SOM was quantified, and fungal and bacterial abundance were quantified by qPCR of the ITS region and 16S rRNA genes, respectively.
Results/Conclusions
In the organic horizon, SOM content either slightly decreased (-2%) or was unchanged when compared to the control. In the mineral horizon, all disturbance treatments led to reduced SOM content compared to the control, with fire + gap + herbivore exclusion plots harboring 30% less SOM as compared to the control. Fungal abundance generally increased in the organic horizon across all treatments, with the most positive effect in +fire plots (266-268%). Fungal abundance in the mineral horizon generally decreased in all treatments (-37%), with the exception of the + fire + gap treatment, where it increased (+172%). Bacterial abundance generally decreased (-17%) in the organic horizon across all disturbance treatments with the exception of fire + no herbivory, where bacterial abundance increased 72%. Disturbance effects on bacterial abundance in the mineral horizon were variable, with no strong trends emerging. Taken together, our findings suggest the organic horizon SOM may recover from disturbances more quickly than mineral horizon SOM. Unlike the above-ground findings, herbivory does not appear to compound the SOM losses observed after fire or canopy gap creation. The inconsistency in fungal and bacterial responses suggests they may be influenced by disparate factors.