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USDA Forest Service, Grant Number: 16-CS-11242306-135


Two types of analysis were run.

I. Probability of finding L. terrestris in habitat types of the Ottawa National Forests.

Abstract: Parts of the Ottawa National Forest (ONF) provide suitable habitat for invasive earthworms. Extensive earthworm invasion is a relatively recent event on the ONF and this study captures the current state of the earthworm invasion through a four-stage invasive species distribution model (iSDM). The random distribution of earthworms indicates early colonization by earthworms which is moderated by habitat (forest type, soil group, and drainage class). CART modeling was used to determine probability of earthworm invasion. The CART model had a relatively low R2 (0.256) which is a result of the early stage of the earthworm invasion. The probability of finding L. terrestris increased in habitat which is generally considered better habitat.

II. Changes in Carbon and Organic Matter due to earthworm invasion on the Ottawa National Forest.

Abstract: Earthworms, due to their feeding habits, may impact O horizons and soil C, an important component in the global carbon cycle. We compared O horizon thickness (O, Oi, Oe, Oa) and %C in the O, Oi, Oe, and Oa horizons; in mineral soil layers with thicknesses of 0-15 (defined as M1), 15-30 (defined as M), and 0-30 (defined as M) cm; and a ratio of %C in M1:M2 using t-tests. Separate t-tests on each of the soil horizons/layers/ratios were conducted with two dependent variables: the presence/absence of L. terrestris and the presence/absence of all earthworm species. When necessary a general linear model was developed to further explore the C relationships at site with different landscape characteristics. Similar to many other studies we found no relationship between %C and the class variables. Organic horizons had horizon depths that were significantly smaller at sample sites where earthworms were present.