Plant species richness determinants in ephemeral ponds and permanent wetlands

Abstract

Ephemeral ponds (EPs) are wetlands that dry seasonally and are common in the forests of northern Wisconsin. We examined relationships between several environmental factors and plant species richness (number of species) in 43 EPs and 14 permanent wetlands (PWs) located in the Chippewa Moraine State Recreation Area. We used multiple linear regressions to identify significant relationships between environmental attributes and plant species richness. PWs had higher plant species richness than EPs, possibly due to their larger size and more stable hydrology. In EPs, chlorophyll-a was positively related to plant species richness, while pH and water depth were negatively related. In PWs, pH and SRP were strong negative predictors of plant species richness. Species richness may have been higher in low pH wetlands due to the addition of acid-loving species. High chlorophyll-a (algae) in EPs may have indicated a decrease in light limitation for vascular plants. In PWs, high SRP may have decreased species richness due to the dominance of competitive plant species. Plant species richness was significantly higher in wetlands dominated by dry hummock compared to wet pool/flat-type microtopography in both wetland types. The stable water levels in PWs make microtopographic variation more important for small-scale richness. Our results indicate that EPs may not be as important for vegetation conservation as PWs, and EPs may not be as susceptible to phosphorus pollution as PWs. With climate change causing less frequent but more intense precipitation events, more generalist species may increase in all types of wetlands, but especially EPs.