University of Massachusetts Amherst

Conservation Assessment and Prioritization System

Conservation Assessment and Prioritization System

Data Accuracy and Limitations

The GIS data used in CAPS come from a variety of sources, and the quality of these data are variable. We integrated these data sources into a single land cover map, with several parallel data layers, including settings variables and other ancillary layers. We put considerable effort into integrating these input layers in ways that maximized the accuracy of available data, while making sure the final map generally makes sense, both visually and for use in the CAPS metrics. Because input data came from several different sources, we have no estimate of the accuracy of the final data set, nor of the effect errors in the base map may have had on final CAPS results.

CAPS Input Data Layers describes the GIS data used by CAPS.

Nobody should have any illusions that the base map presents a “true” depiction of the landscape—a comparison of the land cover with aerial photos or with familiar places will turn up errors in classification and position. Furthermore, the classification is fairly coarse, and distinctions between classes such as marsh and shrub swamp are necessarily arbitrary. Many of these communities change over time, so our snapshot based on data generated over several years may depict today’s beaver pond as yesterday’s forested wetland.

We believe that the effects of many of the data errors will be relatively small. CAPS operates at fairly broad scales, looking at the effects of the surrounding landscape on any particular point. Small errors in classification and placement (small roads and streams omitted, marshes slightly shifted, small forest patches lost because of the grain of the map) will usually have minor effects on final results.

The coarseness of the classification scheme is perhaps a larger issue. Available data necessitated lumping many different forest communities into a single class; likewise, many rare and small-patch-forming communities were omitted. This leaves CAPS unable to compare patches of rich mesic forest to other patches of rich mesic forests, or to evaluate acidic rocky outcrops. To the extent possible given data limitations, the settings variables are meant to distinguish among communities at a fine scale; these settings variables are used in the similarity, connectedness, and aquatic connectedness metrics.

It is important to keep in mind that CAPS is an assessment of ecological integrity—the ability of species and natural systems at a site to persist over time in the face of stressors. It is explicitly not a model of biodiversity per se, as many species (especially plants) thrive in anthropogenically disturbed areas that we do not rate high. Although such areas are important to conservation, we made the decision to focus on relatively natural areas that could be subject to land protection. Comprehensive action to protect biodiversity must include both protecting large areas of land with high ecological integrity (known as the “coarse filter” approach to conservation; Hunter et al. 1988) as well as protecting specific sites with rare species or high species richness, including anthropogenically modified sites (the “fine filter”).

CAPS Ecological Community Descriptions provides description of ecological communities.

CAPS Ecological Settings Variables lists and describes the ecological settings variables used in CAPS.

CAPS is a comprehensive assessment (models are applied uniformly to all areas) and relies on data that are broadly available across Massachusetts. The Index of Ecological Integrity is meant to give a general estimate of the integrity of a site, but we recommend using it in conjunction with other data in order to get a fuller picture of ecological status of areas within Massachusetts, including:

  • Sources of degradation that may be mapped but are difficult to model (e.g., toxic pollution)
  • Sources of degradation that are not comprehensively mapped (e.g., past land use)
  • Data that might suggested increased conservation value but that are not comprehensively mapped (e.g., certified vernal pools, rare species records or rare natural communities)
  • Data that might suggest higher conservation value not related to ecological integrity (e.g., protected status, inclusion within an ACEC)
  • Information on populations or habitat of species of conservation concern