Coastwide Reference Monitoring System (CRMS) Vegetation Volume Index: An assessment tool for marsh habitat focused on the three-dimensional structure at CRMS vegetation monitoring stations

A Vegetation Volume (VV) variable and Vegetation Volume Index (VVI) have been developed for the Coastwide Reference Monitoring System (CRMS). The VV is a measure of the amount of three-dimensional vegetative structure present at each CRMS site and is based on vegetation data collected annually. The VV uses 10 stations per CRMS site to quantify four vegetation layers: carpet, herbaceous, shrub, and tree. For each layer an overall live vegetation percent cover and height are collected to create a layer volume; the individual layer volumes are then summed to generate a site vegetation volume profile. The VV uses the two-dimensional area of live vegetative cover (in square meters) multiplied by the height (in meters) of each layer to produce a volume (in cubic meters) for each layer present in a 2-meter by 2-meter station. These layers are additive, yielding a total volume for each of the 10 herbaceous vegetation stations and an overall CRMS marsh site average.

The VV is an assessment of the quantity of vegetation present and is directly related to plant community structure. The VV differs from the previously developed Floristic Quality Index (FQI) in that the VV makes no assumptions about vegetation quality, giving each species equal weight; the FQI scores species with consistent site fidelity more favorably. We adapted the VV data into the VVI, which creates a representative score for all coastal marsh types. A VV and VVI will be generated annually for CRMS site, project, and basin-level analysis. The index is designed to assess areas undergoing habitat conversion, creation, and disturbance and to document project effectiveness when goals are to create, increase, or maintain emergent vegetation.

The VV and VVI will be used to establish trends, to make comparisons, and to evaluate restoration projects. Assessments that rely on the VVI will be included in appropriate Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) project reports and analyses. Implementation of the VVI will give coastal managers a new tool to design, implement, and monitor coastal restoration projects. A yearly trajectory of site, project, basin, and coastwide VVI will be posted on the CRMS Web site as data are collected. The primary purpose of the tool is to assess CWPPRA restoration project effectiveness, but it will also be useful in identifying areas in need of restoration and in coastwide vegetation assessments.