HGM and wetland functional assessment: Six degrees of separation from the data?

Ecologists routinely use rapid assessment protocols to try and determine level of function for wetlands. In the United States, one of the more intensively used approaches is the hydrogeomorphic (HGM) approach. Using this system, wetlands are classified by their location, the source of water, and their hydrodynamics. Models are built to attempt to determine levels of function, but models rely almost exclusively upon structural indicators that may, or may not, relate in any meaningful way to function. In this paper I examine several models from Pennsylvania where a considerable amount of data exists for the sites from which the models were developed. I show that, even with a large data set, models still rely upon structure with a tenuous connection to real function. I then examine several other models from around the United States related to hydrology, and assess the relationship of the models to actual function. Suggestions for change include slowing the permit process down, continuing to develop large sets of reference wetlands, reducing the use of indices within indices, and developing a research agenda that addresses the relationships between structure and function.