Drainage ditches and many other manmade aquatic features are often assumed to have low ecological value, but such systems are poorly characterized. In addition, artificiality, per se, is not an ecological process that accounts for ecosystem structure and function. We hypothesize that the actual explanatory variables in these systems are some combination of watershed setting, design, including initial construction and subsequent management, and time since design interventions. In summer 2015, we surveyed 32 freeway, agricultural, and forested ditches in the North Carolina Coastal Plain for vegetation, soil, hydrology, and morphology, to see under what conditions these ditches manifest wetland structure.
Results/Conclusions
Freeway, agricultural, and forested ditches hosted different herbaceous vegetation communities (F=17.2, d.f.=2, p=0.001) with similar wetland indicator statuses, all more wetland than upland. Agricultural sites had greater coverage of obligate wetland species than other site types (F=7.09, d.f.=2, p=0.007), but agricultural sites also had more facultative upland plants, and other wetland indicator classes were similar across site types. Herbaceous vegetation height (F=14.5, d.f.=1, p=0.002) and the interaction of site type and canopy cover (F=4.12, d.f.=2, p=0.039) also correlated with obligate coverage, suggesting that mowing and pruning regimes may influence wetland plants. In conclusion, ditches respond to known aquatic ecological drivers.