Historical land use change alters the structure of forest floor invertebrate communities

Background/Question/Methods

Invertebrate communities provide important ecosystem functions, such as assisting in decomposition, serving as resources for consumers, and participating in interactions, such as pollination, seed dispersal, and predation. Understanding anthropogenic impacts on invertebrate community structure is important towards conserving ecosystem functions in natural systems. In North American forests, a historical form of anthropogenic impact is clearing for agriculture. Most forests in the northeast are secondary and have regenerated from previous clearing. While some forest components regenerated, such as woody plant communities, less is understood about impacts on forest invertebrate communities. We performed a large natural experiment to examine if forest land use history impacts ground invertebrate community structure. We collected specimens using pitfall traps in 15 plots (5 m2) in 20 paired primary and secondary forests in three northeastern regions. First, we sorted specimens into broad taxonomic groups and measured total and taxonomic group abundance. We estimated biomass at the total and taxonomic group level by photographing specimens and measuring surface area and average particle size using ImageJ. We are assessing diversity of three focal taxonomic groups that are forest indicators or functionally important, Formicidae, Arachnida, and Coleoptera, by identifying specimens to the lowest taxonomic unit.

Results/Conclusions

We found that Arachnida and Diplopoda abundances were higher in primary forests, while Gastropoda abundance was higher in secondary forests with region also explaining variation. Abundances of Formicidae, Collembola, Diptera, Acarina, and Orthoptera were influenced by region, but not land use history. Primary forests had higher total invertebrate biomass than secondary forests, and region had an effect. Land use history had no effect on average particle size and total invertebrate abundance, but there was variation among regions. Forthcoming analyses will examine the impact of land use history on biomass of broad taxonomic groups and diversity of focal groups. We identified Formicidae and found 40 species. Preliminary results on Formicidae species suggests no effect of land use history on richness, but changes in community composition. Our results demonstrate that historical land use change affects forest floor invertebrate community structure. Secondary forests have lower total invertebrate biomass, with varying effects on groups. Better understanding the responses of focal groups to historical land use can provide insight on forest health and how to best manage for maintaining ecosystem function. Ultimately, this work demonstrates land use change may indirectly impact ecosystem function by restructuring forest floor invertebrate communities.