| Seventeen wetland mitigation sites in eastern Nebraska were evaluated, by vegetative zone, to assess the relative success of active and passive wetland vegetation establishment techniques. For sites with available records of species introduced, 46% of the seeded species and 31% of the transplanted species were successfully established suggesting that the intentional introduction of species (i.e. active methods) provides some degree of success in wetland creation. No significant differences were observed within or among active or passive methods for Species Richness (S), Shannon-Wiener diversity (H'), or the Floristic Quality Index (FQI) (Kruskall-Wallis test P < 0.05). However, while not statistically significant, general trends showed that, in the temporarily flooded zones, seeding resulted in both the highest overall plant diversity and highest FQI (S = 20.2, H' = 1.74, FQI = 8.99) and, among species with cover values > 0.5%, the lowest percent non-native species (6.2%). In the seasonally flooded zone, the highest diversity and highest FQI resulted from a combination of seeding and the addition of donor soil and transplants (S = 30.0, H' = 2.598, FQI = 19.1). This combination of treatments also had the lowest percent of nonnative species with canopy cover values > 0.5% for the seasonally flooded zone (0.0%). In contrast, the highest diversity and highest FQI values in the permanently flooded zone were observed with the addition of donor soil (S = 13, H' = 1.191, FQI = 9.6), although the percent of nonnative species with canopy cover values > 5% was lowest with a combination of seeding and the addition of donor soil and transplants. General trends shown in this study suggest that, among currently recommended procedures for vegetation establishment in wetland creation, active techniques, such as, seeding, donor soil addition, and transplanting, are equally or more effective in obtaining both higher diversity and floristic quality and fewer non-native species than are passive techniques, such as natural colonization. A combination of methods may also be successful in creating wetland plant diversity, although the result was only noted for the seasonally flooded zone. The results of this study provide information that should be useful in creating wetlands until more rigorous studies on the process are completed. The study also provides a database against which future assessments of the study sites may be compared. |
