Date of Award

January 2018

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Stephen C. Richter

Second Advisor

Kelly Watson

Third Advisor

Jonathan M. Malzone

Abstract

Wetlands fulfill many vital ecological functions, including providing habitat for amphibians and plants. Some wetlands, known as upland-embedded wetlands (UEWs), are depressional wetlands surrounded completely by upland habitat. This wetland type has been constructed in many areas for conservation and mitigation purposes, but constructed UEWs often do not function equivalently to natural wetlands, and often have different physical and chemical characteristics. In the Daniel Boone National Forest (DBNF), numerous UEWs have been constructed on ridge-tops to benefit game and bat species. Previous studies have shown that many of these constructed wetlands have permanent hydroperiods and different amphibian communities than co-occurring natural ephemeral wetlands. Wood frog and marbled salamander larvae are found almost exclusively in natural wetlands and green frog larvae and eastern newts are found in constructed wetlands. It is currently unknown whether plant communities at these constructed wetlands are similar to those of co-occurring natural wetlands. My objectives were to a) gain a more complete understanding of the amphibian communities in the ridge-top wetland system of the DBNF, b) to determine if previous amphibian findings are generalizable across the large number of UEWs that have been constructed, c) to determine if plant communities differ between natural and constructed UEW sites, d) to understand the environmental and habitat variables that influence plant communities, and e) to synthesize previous findings with my own research to make management and research recommendations for the constructed UEW system in the DBNF.

I measured amphibian catch-per-unit effort and wetland habitat variables at 48 wetlands (10 natural, 6 previously-studied constructed, and 32 randomly-selected constructed). I used Kruskal-Wallis tests, generalized linear models, and nonmetric multidimensional scaling to compare conditions among wetland types and to visualize amphibian communities. Natural wetlands were associated with wood frogs (Lithobates sylvaticus) and marbled salamanders (Ambystoma opacum) and constructed wetlands were associated with green frogs (L. clamitans), eastern newts (Notophthalmus viridescens), and spotted/Jefferson salamanders (A. maculatum, A. jeffersonianum). Four-toed salamanders (Hemidactylium scutatum), cricket frogs (Acris crepitans), toads (Anaxyrus spp.), and chorus frogs (Pseudacris spp.) showed no clear patterns related to wetland construction history. Constructed wetlands had higher amphibian richness and diversity than natural wetlands. Hydroperiod was a major driver of community composition. The introduction of permanent water sources has allowed permanent-wetland obligate species, including newts and green frogs, to colonize the UEW system. These species prey on wood frog eggs and larvae and increase the threat of disease introduction and transmission. My findings supported previous research in the system, indicating that this pattern is representative of the more than 500 constructed wetlands throughout the Cumberland Ranger District. With amphibian declines due to habitat loss, constructed and restored wetlands provide important breeding habitat. Under some climate models, hydroperiods of existing ephemeral wetlands are projected to shorten, disrupting breeding cycles and causing larval death. It is important that constructed wetlands provide habitat that is both structurally and functionally similar to natural reference habitat.

I evaluated differences in plant communities at 10 natural and 10 constructed upland-embedded wetlands in the DBNF. I estimated cover class of each understory species in several plots at each wetland and performed visual surveys to capture total species richness at each site. I also measured habitat variables at these sites. Using Mann-Whitney U tests, I found that natural and constructed wetlands differed significantly (α = 0.05) regarding total and nonnative species richness, which were higher at constructed wetlands; and mean coefficient of conservatism, floristic quality, and percent canopy closure, which were higher at natural wetlands. Using cluster analysis and nonmetric multidimensional scaling (NMDS) with post-hoc PERMANOVA comparisons, I determined that understory vegetative communities were significantly different between wetland types. Permanent hydroperiod and a history of disturbance at constructed wetlands have resulted in these sites having lower floristic quality, lower ecological conservatism, and more invasive species than natural wetlands. Closed canopy at natural sites increases presence of shade-tolerant understory species. More research is needed to separate the effects of construction history, canopy closure, and hydroperiod on understory communities, richness, and floristic quality.

Management and additional research are recommended in the UEW system in the DBNF. Research should address amphibian and plant communities at natural and constructed UEWs throughout all districts of the DBNF, including population dynamics of marbled salamanders, effects of landscape and geologic features on wetland hydrology, and detection and mapping of undocumented UEW sites. Management should focus on conserving existing natural UEWs, reducing the number and density of constructed UEWs, altering a subset of constructed wetlands to encourage natural-type conditions, and removing invasive species from wetland sites. Amphibian community and habitat characteristics should be assessed to select candidate wetlands for alteration or removal. Methods could include draining wetlands by altering dams and shortening hydroperiods by decompacting soil, lowering dams, and planting trees. Post-alteration, plant and amphibian communities should be monitored for at least six years. Prudence and planning are urged in all wetland construction and alteration projects to ensure that the constructed wetlands will meet desired ecological goals and not disrupt existing ecosystem structures.

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