Date of Award
Program or Major
Natural Resources and Environmental Studies
Doctor of Philosophy
Kimberly J Babbitt
Mark J Ducey
Charles A French
Freshwater wetland ecosystems are a valuable resource, but current policies fail to prevent their continuing destruction. Policy-makers increasingly use decentralized wetland-buffer programs to address such policy failings, but scant research has evaluated whether these programs are both ecologically and socially effective. In the following dissertation, I address this gap using two complementary projects.
For the first project, I assessed whether forested buffers are an effective tool for maintaining viable populations of pool-breeding amphibians. Such species spend their early life stages in vernal pools, which are small, highly productive wetlands, but use the surrounding forest during juvenile and adult life-stages. Though buffers are often prescribed for managing these species, buffer utility has never been experimentally tested. For this project, I used data from a landscape-scale experiment to determine whether wider buffers more efficiently mitigate the effects of forest disturbance on breeding-adult populations of spotted salamanders (Ambystoma maculatum) and wood frogs (Lithobates sylvaticus), two amphibian species that breed in vernal pools throughout eastern North America. This experiment was conducted at 11 natural vernal pools in an industrial forest in east-central Maine. Each pool was randomly assigned to one of three treatments (i.e., reference, 100m buffer, 30m buffer). Clearcutting was used to create experimental buffers. All spotted salamanders and wood frogs breeding in these pools over the six study years were captured, counted, sexed, and sized. I used generalized linear mixed effects regression to assess the relative impacts of buffer treatment and pool hydroperiod on breeding-adult population size, composition, and biomass.
I found that clearcutting resulted in negative impacts to breeding-adult populations, but that buffer width was an important mitigating factor in the extent of these impacts. Specifically, narrower (30m) buffers were associated with altered salamander sex ratios, and for both species, diminished body size, condition, and biomass and fewer recaptures. In the wider (100m) buffer treatment, I detected negative effects on salamander sex ratios and abundance, and the biomass of both species. However, the 100m-treatment effects were largely limited to pools that were also stressed hydrologically. The observed negative effects potentially signal reduced local-population resiliency, which could scale up to regional-population and community-level effects, especially if other stressors were introduced to the system. Several, though not all, of the negative effects started to recover as the cuts regenerated, however, suggesting a temporally-finite window of reduced resiliency. Overall, these results provide the first experimental evidence showing that buffers that are only 30m wide may be insufficient for maintaining resilient local populations of pool-breeding amphibians.
Whereas for my first project, I focused on the value of buffers for wildlife in a forestry setting, for my second project I examined decentralized wetland-buffer programs in exurban towns. In New England, many municipalities have local wetland-permit policies and land-use decision-making is largely devolved to municipal boards. While some evidence suggests that local wetland programs minimize development in and near wetlands, it does not explain why towns with similar programs sometimes have very different wetland-protection outcomes, if stakeholders support local wetland programs, or whether social outcomes feedback to influence ecological outcomes. I used case-study analysis to determine the specific factors driving, and the potential for interactions between, the ecological and social effectiveness (EE and SE) of municipal wetland-permitting programs in four southern New England towns. To assess EE, I used regression techniques to quantify spatial impacts to wetland ecosystems on 50 construction site plans per town. To determine SE, I conducted and qualitatively coded 45 key-informant interviews.
I found that EE and SE both varied considerably across the four towns, despite broadly similar wetland-policies and demographic profiles. EE was largely a function of SE and policy details. In turn, SE was driven by multiple interacting factors, with no single prescription fitting all towns. Nevertheless, I did identify eight principal SE drivers that strongly shaped, facilitated, or were used to express SE. These included: having a conservation-based town identity, being able to communicate about wetland permitting, property-rights ethics, town organizational structure, education, wealth, public participation, and local politics. The case-studies show that local buffer programs can effectively protect wetlands if the necessary social factors are aligned. When social factors do not align, however, stakeholder malcontent can weaken EE and destabilize social relations. To help safeguard against such negative fallout, I provide a set of recommendations intended to enhance the SE and EE of local wetland programs.
My research results, when combined and synthesized with previous research, ultimately indicate that buffers are critical for wetland-ecosystem integrity, but that wider buffers are needed than those currently used in developed landscapes. Equally important, however, the synthesized evidence suggests that buffers alone are an insufficient tool for protecting wetland ecosystems. Rather an effective wetland-management strategy must nurture the social dynamics associated with wetland-program implementation and integrate buffer policies with landscape-scale conservation planning.
Veysey Powell, Jessica, "Conserving wetlands for humans and amphibians: a multidisciplinary approach to understanding the social and ecological effectiveness of New England's wetland policies" (2014). Doctoral Dissertations. 2160.