Citation:

Magee, T., K. Blocksom, AND S. Fennessy. A national-scale vegetation multimetric index (VMMI) as an indicator of wetland condition across the conterminous United States. ENVIRONMENTAL MONITORING AND ASSESSMENT. Springer, New York, NY, 191:322, (2019). https://doi.org/10.1007/s10661-019-7324-4

Impact/Purpose:

One of the greatest challenges to continental-scale wetland assessment is defining an effective biological indicator of ecological condition that is comprised of a consistent suite of easy-to-measure metrics, and which is relevant across large scales and various kinds of wetlands. We address this problem by developing a vegetation multimetric index (VMMI) of biological condition for the first National Wetland Condition Assessment (NWCA) spanning the conterminous United States (US), conducted in 2011 by the US Environmental Protection Agency and partners. We detail an objective, repeatable process for evaluating numerous candidate condition metrics and constructing a parsimonious national-scale vegetation index. The resulting VMMI includes four metrics (floristic quality index, relative importance of native species, richness of disturbance-tolerant species, and relative cover of native monocots) and is applicable to diverse wetland types at continental and regional scales. VMMI values from 967 probability sites sampled in the NWCA were used to estimate wetland area in good, fair, and poor condition, nationally and for each of 10 ecoregion by wetland type reporting groups. Strengths and limitations of the national VMMI are highlighted. Results of this work include: 1) a VMMI useful at national or regional scales, or by states, to support monitoring and assessment and inform wetland protection and management, 2) the first national-scale assessment of wetland biological condition, 3) description of condition patterns in ecoregion by wetland type reporting groups, and 4) a baseline for assessing trends in biological condition over time. This research also contributes to work under SSWR Task 3.01A, subtask 1.1.

Description:

In 2011, the United States Environmental Protection Agency (USEPA) and its partners conducted the first National Wetland Condition Assessment (NWCA) at the continental-scale of the conterminous United States (US). A probability design for site selection was used to allow an unbiased assessment of wetland condition. We developed a vegetation multimetric index (VMMI) as a parsimonious biological indicator of ecological condition applicable to diverse wetland types at national and regional scales. Vegetation data (species presence and cover) were collected from 1,138 sites that represented seven broad estuarine intertidal and inland wetland types. Using field collected data and plant species trait information, we developed 405 candidate metrics with potential for distinguishing least-disturbed (reference) from most-disturbed sites. Thirty-five of the metrics passed range, repeatability, and responsiveness screens and were considered as potential component metrics for the VMMI. A permutation approach was used to calculate thousands of randomly constructed potential national-scale VMMIs with 4, 6, 8, or 10 metrics. The best performing VMMI was identified based on limited redundancy among constituent metrics, sensitivity, repeatability, and precision. This final VMMI had four broadly applicable metrics (floristic quality index, relative importance of native species, richness of disturbance-tolerant species, and relative cover of native monocots). VMMI values and weights from the survey design for probability sites (n = 967) were used to estimate wetland area in good, fair, and poor condition, nationally and for each of 10 ecoregion by wetland type reporting groups. Strengths and limitations of the national VMMI for describing ecological condition are highlighted.

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