Changes in invertebrate communities along a natural elevational climate gradient at the Hubbard Brook Experimental Forest, New Hampshire, USA

Warmer winters associated with climate change are predicted to decrease snow cover and increase soil freezing. Previous studies found that increased soil freezing decreased nutrient cycling along a natural climate gradient at the Hubbard Brook Experimental Forest in New Hampshire, USA. The natural climate gradient is similar to what is predicted for climate change in the northeastern US in the next 50-100 years. Compared to north-facing higher elevation sites, south-facing lower elevation sites experience drier and warmer conditions, with less snow cover and increased soil freezing. Soil invertebrates play a key role in decomposition and nutrient transport. We investigated whether a natural climate gradient caused by elevation and aspect in the HBEF affected the richness and abundance of soil invertebrate communities. In June 2011, 54 leaf litter samples and 72 soil samples (divided into 0-5cm and 6-10cm depths) were collected across 18 study sites along the natural climate gradient. Invertebrates were collected from litter and soils using the Berlese and Baermann funnel methods. Invertebrates were stored in ethanol and identified to order when possible. All data were analyzed on a per gram dry weight litter or soil basis.

Leaf litter showed significantly greater invertebrate abundance and richness compared to soil. Leaf litter invertebrate abundance and richness significantly decreased with increased elevation. This trend showed a stronger correlation in south-facing sites, which suggests that increased soil freezing in south-facing sites may have a greater affect on the invertebrate communities. Mites, spiders, and pseudoscorpions showed significant decreases in abundance with increasing elevation. Mites and millipedes had higher abundances on south-facing sites compared to north-facing sites. The 0-5cm soil depth showed significantly greater invertebrate abundance and richness compared to the 6-10cm soil depth. Significant trends associated with increased soil freezing included increased invertebrate richness, nematode abundance, and beetle abundance. Nematode abundance showed a stronger correlation in the 6-10 cm soil depth, suggesting that frost is driving nematodes into deeper soil. Our results suggest that a natural climate gradient at the HBEF has a significant affect on the invertebrate community. Increased soil freezing may be changing the trophic structure of these decomposer communities, and may in turn change decomposition rates. This study is the first description of the invertebrate community along the natural climate gradient at the HBEF, which will be useful for future decomposition and nutrient cycling studies.