Performance trajectories: An alternative to reference wetlands for assessing forested wetland restoration success

Development of forested wetlands created following drastic landscape alterations resembles primary succession.  Therefore, it is difficult to assess recently created forested wetlands by comparison with reference wetlands.  Performance trajectories are a promising alternative to reference wetlands for assessing restoration.  Two trajectory models have been developed using time series data from a single restored site (or a suite of sites) or data from many sites of varying ages.  This research addressed the development and application of the trajectory approach for assessing adequate site progress for created forested wetlands and differs from previous efforts by comparing the current condition of a created wetland to its anticipated condition estimated from wetlands created under similar conditions. The main objective of this research was to: 1) identify parameters exhibiting clear and statistically significant trajectories; 2) calculate 95% confidence intervals around the trajectories; and 3) estimate the required sampling intensity for assessing each indicator. Statistically significant trajectories were identified for four canopy parameters: height; diameter at breast height (dbh); stand basal area; and canopy cover.  Several understory plant functional groups exhibited statistically significant trends when wetlands were grouped by hydrology.  Moderate increases were detected in subcanopy dbh and basal area. Moderate decreases were noted for understory species richness, diversity and frequency of a range of plant functional groups. This trajectory approach is a theoretically sound method for assessing forested wetland restoration and can be used to assess whether future wetland creation is progressing at a minimum no worse and, ideally, better than occurred in the past.