This document describes a suite of stressor metrics that assess different aspects of the effects of roads and development on ecological integrity (see technical document on integrity, McGarigal et al 2017). They share a common algorithm, but each has unique parameters. These metrics are obviously highly correlated, but each assesses a different aspect of the effects of roads and development on ecological integrity. These metrics are elements of the ecological integrity analysis of the Designing Sustainable Landscapes (DSL) project (McGarigal et al 2017). Consisting of a composite of 21 stressor and resiliency metrics, the index of ecological integrity (IEI) assesses the relative intactness and resiliency to environmental change of ecological systems throughout the northeast. These stressor metrics range from 0 (no effect) to 1 (severe effect). See Table 1 for parameters for each metric. Habitat loss. Assesses the intensity of past habitat loss caused by all forms of development. Direct habitat loss is the primary cause of species decline and extinction; this metric is an index of indirect habitat loss—the decline of integrity in remaining natural lands due to the loss of former habitat in the neighborhood to past development. Mowing and plowing. Assess the intensity of agriculture in the neighborhood as a surrogate for mowing and plowing rates, which are direct sources of animal mortality. Agricultural machinery is a well-known cause of mortality for grassland bird nestlings and terrestrial and semi-aquatic turtles. Microclimate alterations. Assesses microclimatic alterations due to edge effects, such decreased moisture, higher wind, and more extreme temperatures. This metric includes the effects of both anthropogenic edges and natural edges (e.g., the effects of an open marsh on the surrounding forest). Edge predators. Assesses the effect of human commensal mesopredators such as raccoons and skunks. Mesopredators often reach unusually high densities near human habitation, both due to food subsidies (garbage, bird feeders, and livestock grain) and mesopredator release. Domestic predators. Assesses the effect of domestic predators (primarily housecats) due to development. Both pet and feral housecats kill large numbers of birds and small mammals. Invasive plants. Assesses the effect of non-native invasive plants. Invasive plants often spread from sources in residential and agricultural areas, from humandisturbed areas, and along roads. Invasive earthworms. Assesses the effect of non-native invasive earthworms. In the glaciated northeast, all terrestrial earthworms are non-native. Spreading from agricultural areas, home gardens, and fishing holes, they speed up the nutrient cycle in nearby forests, often greatly affecting understory plants and seedling regeneration.
Environmental Sciences | Sustainability
McGarigal, Kevin; Compton, Brad; Plunkett, Ethan; DeLuca, Bill; and Grand, Joanna, "Designing Sustainable Landscapes: Habitat loss, mowing and plowing, microclimate alterations, edge predators, domestic predators, invasive plants, and invasive earthworms metrics" (2018). Data and Datasets. 33.