Effects of forest management on earthworm activity: Testing the relationships of microclimate, soil properties and soil microbial communities in second growth northern hardwood forests

Background/Question/Methods

Recent evidence indicates the introduction of exotic earthworm communities into forests historically devoid of native earthworms causes change within the plant and soil microbial community. These changes have consequences for carbon storage and nutrient dynamics of the forest ecosystem. We experimentally manipulated forest structure in a second-growth northern hardwood forest in north-central Wisconsin to test the linkages between forest structural elements and ecosystem function. By creating gaps and adding coarse woody debris we altered the microclimate that influences earthworm activity. We measured earthworm activity, litter inputs, light availability, soil moisture, temperature, soil carbon and nitrogen, fine root biomass, and identified the soil microbial community in experimental treatments. We used linear mixed models to identify key relationships among measured variables and earthworm activity. Additionally, we will test for interactions with presence and absence of white-tailed deer, another forest stressor present in northern forests.

Results/Conclusions

We measured significant change in the earthworm community over time that was related to the experimental treatments as well as other biotic and abiotic variables. At least 10 earthworm species are present and densities range from 3 to 275 earthworms/m² across the site. The most common genera are Lumbricus, Aporroctodea, and Octolasion.  Variation in earthworm density across the site was described by foliage inputs (quantity and quality), soil microbial biomass and composition, and changes in the microclimate caused by the experimental treatments. The variability in the distribution of Lumbricus biomass across the site was related to experimental treatments, soil organic carbon and soil microbial community composition. Analyses are ongoing to test our understanding of the influence of the earthworm community on the soil carbon cycling in this northern hardwood forest.