Citation:

Magee, T., K. Blocksom, AND A. Herlihy. A simple nonnative plant indicator (NNPI) for describing ecological stress: Application to wetlands of the conterminous United States. To be Presented at Annual Meeting of the Ecological Society of America, Portland, Oregon, August 06 - 11, 2017.

Impact/Purpose:

This presentation will focus on the development and use of a simple nonnative plant indicator (NNPI) of ecological stress. Nonnative plants are recognized indicators of disturbance to wetlands and other ecosystems, and often are direct stressors competing with native plant species and communities, or altering ecosystem processes. Nonnative plant species frequently co-occur and their interactions may have interacting effects on environmental conditions, native vegetation, and other nonnative taxa. The NNPI reflects the collective set of nonnative plant species at a particular location. An application of the NNPI is illustrated using data from the first-ever, USEPA, National Wetland Condition Assessment (NWCA) to estimate the wetland area in conterminous US that falls within four stress categories (low, moderate, high, or very high) defined by the NNPI. The broad audience of the Ecological Society of America's annual meeting is an ideal forum to showcase these methods and to obtain valuable technical input. This interaction will likely increase interest in the USEPA's National Aquatic Resource Surveys and contribute to wetland science and invasion ecology by increasing the number of scientists who will read the NWCA reports and use NWCA data in additional research efforts. This abstract contributes to SSWR 3.01A.

Description:

Background/Question/Methods: Nonnative plants (NNP) are recognized indicators of disturbance to wetlands and other ecosystems, and often are direct stressors competing with native plant species and communities, or altering ecosystem processes. NNP species frequently co-occur and their interactions may have synergistic effects on environmental conditions, native vegetation, and other NNP taxa. We devised a Nonnative Plant Indicator (NNPI) to reflect biological stress from all NNP occurring at particular locations. The NNPI includes three metrics (richness, relative frequency, and relative cover of NNP), which describe different pathways of potential impact. In 2011, the United States (US) Environmental Protection Agency and its partners conducted the first National Wetland Condition Assessment (NWCA), using a survey design permitting extrapolation of results to wetland populations at national and regional scales. Plant species identity and abundance data were collected at 967 probability sites distributed across the conterminous US. We used these data to calculate the component NNPI metrics and then designate a categorical NNPI stressor-level (low, moderate, high, and very high) for each site based on defined thresholds for each metric. Using the R package 'spsurvey', wetland area occurring in each NNPI stressor-level category was estimated for the conterminous US, five large ecoregions, and four broad wetland types. Results/Conclusions: Our results are applicable to an inference population representing 25.15 +- 2.27 million hectares (ha) of wetland across the conterminous US, and provide a baseline (2011) assessment of stress from NPP. Nationally, for this population, 61 +- 4.9% (15.26 +- 1.70 million ha) of the area had low NNPI, 20+- 4.7% (5.17+- 1.31 million ha) had moderate NNPI, while 10 +- 2.4% (2.48 +- 0.59 million ha) fell into high and 9 +- 2.3% (2.24 +- 0.56 million ha) into very high NNPI categories. Wetland area was unequally distributed across ecoregions and wetland types, and percent area in specific NNPI categories varied among these groups. Combined percent area having high and very high NNPI was greater for western ecoregions [western mountains ~29%), xeric west (~87%), and interior plains ~46%)] than for eastern ecoregions [eastern mountains and upper midwest (~11%) and coastal plains (~10%)]. In addition, greater percent area with high and very high NNPI was observed for herbaceous vs. woody wetland, and for inland vs. estuarine wetland. The second NWCA was conducted in summer 2016. Comparison of patterns from 2011 and 2016 will allow initial analysis of NNPI trends. This abstract does not necessarily reflect EPA policy.

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