lished or the likelihood that exotics will not invade. HGM provides no analytical structure (e.g., a decision matrix) for inserting information about factors that influence the likelihood that hydrology, desired wetland vegetation, and desired animals will be reestablished or that exotics will not invade. This can only come with explicit application and monitoring using HGM in the design of wetland mitigation projects, and the resulting feedback on the correspondence between HGM indicators and monitored performance. This gap between HGM, and most other functional assessment procedures for that matter and the need for specific scientific and technical guidance for self-sustaining, functional mitigation wetlands remains a major hindrance to effective wetland mitigation.
It is possible that there is no single “best” wetland assessment procedure, because the specific needs vary with the situation, especially if a quick screening technique is needed (Smith 1993). However, in the mitigation process it is essential that there be an ability to relate the structural characteristics of a site to the resulting functions. Only in that way can the compensation site be designed to secure certain functions. The level of the function is calculated relative to levels in reference sites in the same subclass of wetlands within the same watershed or ecoregion. Perhaps functional assessments will evolve to meet this goal. The functional assessment procedure has the following desirable attributes:
It includes reliable indicators of the important wetland processes (hydrology, sedimentation, and primary production) or a scientifically established structural surrogate of those processes.
It assesses function over a broad range of performance conditions, such that differences in wetlands can be relatively easily distinguished.
It is integrative over space and time, and its indicators are not vulnerable to seasonal or other fine-scale temporal or spatial variability.
It results in a continuous, parametric scale that has not been reduced to a relative rank.
It assesses all recognized functions so that the assessment encompasses all goals for the mitigation.
1. Dependence on subjective, best professional judgment in assessing wetland function should be replaced by science-based, rapid assessment procedures that incorporate at least the following characteristics:
Effectively assess goals of wetland mitigation projects.
Assess all recognized functions.
Incorporate effects of position in landscape.