Soil fauna studies in BES: objectives, methodology and preliminary data (presentation)
Nancy A. Kreiter
Soil communities are responsible for many ecosystem functions. The fauna of these communities processes the majority of dead organic matter and thereby influences the rate of nutrient release. Soil animals also aerate soils and influence the distribution of microorganisms. The composition of soil communities may therefore be important in understanding ecosystem dynamics.
There are many factors that determine the community structure of soil biota. In addition to physical conditions, past and present disturbances can affect both species diversity and abundance. We are interested in understanding the influences of the urban environment on both soil community structure and ecosystem function. Our studies focus on the soil invertebrates near the permanent plots established by BES (Oregon Ridge Park, Leakin Park and Hillsdale). In 1999 we sampled soil macroarthropods and earthworms at these sites using pitfall traps, leaf litter sifting, digging and hand sorting, and extraction.
Extractions at the urban sites at Leakin Park and Hillsdale yielded higher earthworm biomass and densities than at the Oregon Ridge reference site (Fig. 1). Species richness, however, was higher at Oregon Ridge site at Hillsdale (Table 1). A total of eight species were found at Oregon Ridge, two of which were endemic species and one introduced from Asia. The remaining five species were introduced from Europe. In contrast, only three species were found at the Hillsdale site, all introduced, ubiquitous species common in urban areas. This pattern is similar to that found at other urban sites. We expect to find that earthworm densities will have a great influence on the soil community and processes. Preliminary results by Groffman, Pouyat and Lorefice (see abstract) show differences in nitrification rates among the plots.
Figure 1. Biomass (mean ± SE) of earthworms extracted near the BES permanent plots. The Oregon Ridge sampling site is in the vicinity of the upslope plot. Samples were taken in the fall of 1999.
Table 1.Earthworm Species Extracted from BES sites
Preliminary litter sifting and sorting for other soil invertebrates indicated that Oregon Ridge is dominated by Hymenoptera (mostly ants), with a density of 488 ind* m-2, followed by Coleoptera (beetles), Araneidea (spiders), and Diplopoda (millipedes). Pitfall traps yielded somewhat different results, with Diplopoda dominating the samples (25%). This difference illustrates the importance of collection techniques, which can greatly influence the organisms sampled. For example, larvae were caught in greater numbers in the sifted samples than in the pitfall traps. Arthropod abundance was generally low due to the extremely dry summer of 1999. Some site differences were found. Isopods were entirely lacking from the Oregon Ridge site, while Leakin Park was found to have an abundant isopod community. The two dominant species here are Cylisticus convexus, and Trachelipus rathkei, both introduced from Europe.
We intend to continue sampling the soil fauna from the BES sites. Our long-term goals include an inventory of the species that compose the soil communities in the rural-to-urban gradient and field experiments to reveal their role in decomposition and forest ecosystem dynamics.