Small mammals have a legacy effect on an ecosystem that persists following a major disturbance

Background/Question/Methods:

Small mammal herbivores can alter above- and belowground linkages. For example, herbivores can change plant community structure, which might influence nutrient cycling by modifying substrate availability belowground. We examined whether previously measured changes in above- and belowground community structure and ecosystem functioning in a 4-year small mammal manipulation in an old-field ecosystem, would persist following fire disturbance. We predicted (i) burning would ‘reset’ differences in above- and belowground community structure and processes, but (ii) these ‘resets’ would be temporary and legacy effects of small mammals would be evident in both community structure and functioning later in the growing. The old-field ecosystem encompassing our small mammal manipulation was burned with a low-intensity fire by the Tennessee Wildlife Resource Agency on March 15^th, 2012. To explore the effects of fire on community structure, we measured percent cover of the functional plant community and took soil samples for fungal and bacterial abundance and nematode abundance, following the burn. To explore effects of fire on ecosystem processes, we took additional soil samples to examine potential extracellular enzyme activity (EEA) and measured CO₂respiration from the soil.

Results/Conclusions:

Our preliminary results indicate effects of small mammals persist through a disturbance but also influence the ecosystem’s susceptibility to fire through their effects on plant community structure. Mammal access plots had 80% more green vegetation (F=453.91, p<0.001), which reduced susceptibility to burning by 70% (F=64.92, p<0.001), and is partially explained by the previous year’s forb cover (R²=0.25, F=6.14, p=0.023). When we compare functional plant community between 2011 and 2012, we find no change in any functional group’s cover (p>0.050), indicating burning has negligible affects on plant community composition. We found all EEA to be higher post-burn, but only b-glucosidase showed an effect of mammal treatment (F=6.19, p=0.022), with greater activity under mammal exclusion. This follows previous years’ patterns with higher activities across all enzymes measured when small mammals are excluded. While we find a response of belowground processes to mammals immediately post fire, this response appears temporary and effects of mammals persist. We found support for our hypotheses that a major fire may reset the effects of small mammals, but these resets are short-term and the effects of mammals are strong enough to not only persist following a major disturbance, but also influence an ecosystems’ vulnerability to fire.