Novel ways to assess forested wetland restoration in North Carolina using ecohydrological patterns from reference sites

Abstract

Restoring jurisdictional wetland hydrology does not ensure that the hydrologic conditions of any specific natural forested wetland community are recreated. This is especially problematic for a state like North Carolina, which has roughly two dozen different forested wetland communities. Because forested wetland communities align themselves across edaphic and hydrologic gradients, we suggest exploiting these relationships to guide restoration design and set performance standards. However, methods to compare hydrology between multiple reference sites and restored wetlands are lacking. To address this, we studied three different forested wetlands across 13 reference sites to determine which measures of water table levels, based on correlation with plant community composition, would be useful to distinguish these three communities. We then used the best measures of water table levels to assess two restoration sites and compare them with the reference sites. Our results showed that monthly median water table levels encompassing the start of the growing season had the strongest correlation with plant community composition, whereas roughly five other measures also had strong correlations. On the basis of the best measures, both of the restoration sites had water table levels that generally fell within the natural range of the reference sites. Because there was variation in water table levels across each restoration site, the different measures where useful to identify which areas were least similar to the reference sites and might need further monitoring in the future. On the basis of our results, we recommend using community‐specific measures of hydrology to guide and assess forested wetland restoration. Copyright © 2013 John Wiley & Sons, Ltd.

Reference conditions for restoration of heterogeneous Mediterranean wetland are best defined by multiple, hydrologically diverse sites

“…NMDS ordinations displaying species composition centroids for the cluster analysis assemblages showed more coherent and consistent groupings than equivalent centroids for the sites. This supports the idea that differences in vegetation composition between sites were determined largely by hydrological factors (Johnson et al ). A practical consequence is that the species assemblages derived collectively from the sites should provide a more precise basis for defining reference condition than any derived from individual sites.…”

“…Furthermore, higher salinities in the surface layer of soil resulted from evapotranspiration during the dry season and salts leaching from higher areas. Similar diversity in water‐table levels among reference sites has also been reported recently in a study of forested wetland restoration (Johnson et al ).…”

“…For key to assemblage names see Table 1. been reported recently in a study of forested wetland restoration (Johnson et al 2014). These underlying ecohydrological gradients were the rationale for examining the structure and composition of vegetation across all five reference sites in detail.…”

Hydrologic similarity to reference wetlands does not lead to similar plant communities in restored wetlands

“…Restored hydrologic conditions may be more impactful on plant species composition in some wetland types than others (Johnson et al ). Research from North American grasslands has shown increased species sensitivity to rainfall amounts in drier areas compared to wet areas (Cleland et al ).…”

“…One may restore a completely inappropriate hydrologic regime for the given wetland type, yet still have survival and growth of planted species due to their broad hydrologic niche. Restored hydrologic conditions may be more impactful on plant species composition in some wetland types than others (Johnson et al 2014). Research from North American grasslands has shown increased species sensitivity to rainfall amounts in drier areas compared to wet areas (Cleland et al 2013).…”