University of Massachusetts Amherst

Conservation Assessment and Prioritization System

Conservation Assessment and Prioritization System

Data Accuracy and Limitations

The GIS data used in CAPS comes 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 landcover 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 a small but negligible effect on final results. In the future we plan to evaluate the effects of various kinds of errors on CAPS 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 are 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.

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 the assessment area. 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 specific locations within the assessment area, 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)
  • Data that might suggest higher conservation value even though it is not related to ecological integrity (e.g., protected status, classification as an Outstanding Resource Water)