An Experimental Test of Buffer Utility as a Technique for Managing Pool-Breeding Amphibians

Vegetated buffers are used extensively to manage wetland-dependent wildlife. Despite widespread application, buffer utility has not been experimentally validated for most species. To address this gap, we conducted a six-year, landscape-scale experiment, testing how buffers of different widths affect the demographic structure of two amphibian species at 11 ephemeral pools in a working forest of the northeastern U.S. We randomly assigned each pool to one of three treatments (i.e., reference, 100m buffer, 30m buffer) and clearcut to create buffers. We captured all spotted salamanders and wood frogs breeding in each pool and examined the impacts of treatment and hydroperiod on breeding-population abundance, sex ratio, and recapture rate. The negative effects of clearcutting tended to increase as forest-buffer width decreased and be strongest for salamanders and when other stressors were present (e.g., at short-hydroperiod pools). Recapture rates were reduced in the 30m, but not 100m, treatment. Throughout the experiment for frogs, and during the first year post-cut for salamanders, the predicted mean proportion of recaptured adults in the 30m treatment was only 62% and 40%, respectively, of that in the reference treatment. Frog sex ratio and abundance did not differ across treatments, but salamander sex ratios were increasingly male-biased in both cut treatments. By the final year, there were on average, only about 40% and 65% as many females predicted in the 100m and 30m treatments, respectively, compared to the first year. Breeding salamanders at short-hydroperiod pools were about 10% as abundant in the 100m versus reference treatment. Our study demonstrates that buffers partially mitigate the impacts of habitat disturbance on wetland-dependent amphibians, but buffer width and hydroperiod critically mediate that process. We provide the first experimental evidence showing that 30-m-wide buffers may be insufficient for maintaining resilient breeding populations of pool-dependent amphibians, at least during the first six years post-disturbance

Data from: An experimental test of buffer utility as a technique for managing pool-breeding amphibians

Vegetated buffers are used extensively to manage wetland-dependent wildlife. Despite widespread application, buffer utility has not been experimentally validated for most species. To address this gap, we conducted a six-year, landscape-scale experiment, testing how buffers of different widths affect the demographic structure of two amphibian species at 11 ephemeral pools in a working forest of the northeastern U.S. We randomly assigned each pool to one of three treatments (i.e., reference, 100m buffer, 30m buffer) and clearcut to create buffers. We captured all spotted salamanders and wood frogs breeding in each pool and examined the impacts of treatment and hydroperiod on breeding-population abundance, sex ratio, and recapture rate. The negative effects of clearcutting tended to increase as forest-buffer width decreased and be strongest for salamanders and when other stressors were present (e.g., at short-hydroperiod pools). Recapture rates were reduced in the 30m, but not 100m, treatment. Throughout the experiment for frogs, and during the first year post-cut for salamanders, the predicted mean proportion of recaptured adults in the 30m treatment was only 62% and 40%, respectively, of that in the reference treatment. Frog sex ratio and abundance did not differ across treatments, but salamander sex ratios were increasingly male-biased in both cut treatments. By the final year, there were on average, only about 40% and 65% as many females predicted in the 100m and 30m treatments, respectively, compared to the first year. Breeding salamanders at short-hydroperiod pools were about 10% as abundant in the 100m versus reference treatment. Our study demonstrates that buffers partially mitigate the impacts of habitat disturbance on wetland-dependent amphibians, but buffer width and hydroperiod critically mediate that process. We provide the first experimental evidence showing that 30-m-wide buffers may be insufficient for maintaining resilient breeding populations of pool-dependent amphibians, at least during the first six years post-disturbance

Buffer-Mediated Effects of Clearcutting on In-Pool Amphibian Productivity: Can Aquatic Processes Compensate for Terrestrial Habitat Disturbance?

Natural resource extraction and wildlife conservation are often perceived as incompatible. For wetland-dependent amphibians, forested buffers may mitigate timber-harvest impacts, but little empirical research has focused on buffers around lentic habitats. We conducted a landscape experiment to examine how spotted salamander and wood frog reproductive output (i.e., eggmass and metamorph production) respond to clearcutting mediated by buffers of different widths (i.e., uncut, 30 m buffer, 100 m buffer) at ephemeral pools in an industrial forest. We found complex interactions between buffer treatment and reproductive output, which were strongly mediated by hydroperiod. Overall, reproductive output was most sensitive at 30 m-buffer pools and for salamanders, but responses diverged across productivity metrics even within these categories. Notably, for both cut treatments over time, while salamander eggmass abundance decreased, metamorph productivity (i.e., snout-vent length [SVL] and abundance) tended to increase. For example, average metamorph SVLs were predicted to lengthen between 0.2 and 0.4 mm per year post-cut. Additionally, typical relationships between reproductive output and hydroperiod (as indicated by the reference treatment) were disrupted for both species in both cut treatments. For example, long-hydroperiod pools produced more salamander metamorphs than short-hydroperiod pools in both the reference and 30 m-buffer treatments, but the rate of increase was lower in the 30 m-buffer treatment such that a long-hydroperiod pool in the reference treatment was predicted to produce, on average, 24 more metamorphs than a similar pool in the 30 m-buffer treatment. From a conservation perspective, our results highlight the importance of evaluating both terrestrial and aquatic responses to terrestrial habitat disturbance, since responses may be reinforcing (i.e., exert similarly positive or negative effects, with the potential for amplification in the aquatic habitat) or decoupled (i.e., operate independently or be negatively correlated, with responses in the aquatic habitat potentially dampening or counteracting responses in the terrestrial habitat)

Despite Buffers, Experimental Forest Clearcuts Impact Amphibian Body Size and Biomass

<div><p>Forest buffers are a primary tool used to protect wetland-dependent wildlife. Though implemented widely, buffer efficacy is untested for most amphibian species. Consequently, it remains unclear whether buffers are sufficient for maintaining amphibian populations and if so, how wide buffers should be. We present evidence from a six-year, landscape-scale experiment testing the impacts of clearcutting, buffer width, and hydroperiod on body size and condition and biomass of breeding adults for two amphibian species at 11 vernal pools in the northeastern United States. We randomly assigned treatments (i.e., reference, 100m buffer, 30m buffer) across pools, clearcut to create buffers, and captured all spotted salamanders and wood frogs. Clearcuts strongly and negatively impacted size, condition, and biomass, but wider buffers mitigated effect magnitude and duration. Among recaptured individuals, for example, 30m-treatment salamanders were predicted to be about 9.5 mm shorter than, while 100m-treatment salamanders did not differ in length from, reference-treatment salamanders. Similarly, among recaptured frogs, mean length in the 30m treatment was predicted to decrease by about 1 mm/year, while in the 100m and reference treatments, length was time-invariant. Some, but not all, metrics recovered with time. For example, female new-captured and recaptured salamanders were predicted, respectively and on average, to weigh 4.5 and 7 g less in the 30m versus reference treatment right after the cut. While recaptured-female mass was predicted to recover by 9.5 years post-cut, new-captured-female mass did not recover. Hydroperiod was an important mediator: in the 100m treatment, cutting predominately affected pools that were stressed hydrologically. Overall, salamanders and female frogs were impacted more than male frogs. Our results highlight the importance of individualized metrics like body size, which can reveal sublethal effects and illuminate mechanisms by which habitat disturbance impacts wildlife populations. Individualized metrics thus provide critical insights that complement species occurrence and abundance-based population assessments.</p></div

veysey powell and babbitt_data_buffers and amphibians

See ReadMe for explanation of variable names

Experimental design implemented at 11 natural vernal pools in east-central Maine, USA.

<p>Undisturbed buffers of either 100m (left; n = 4) or 30m (right; n = 4) were left adjacent to pools and 100m wide clear cuts were created around the buffers. Forest beyond the clear cut was undisturbed. No cutting occurred at reference vernal pools (not shown; n = 3).</p

Mean and variability of predictor and outcome variables at 11 natural ephemeral pools in east-central Maine, USA.

<p>^a Standard deviation of the pool hydroperiod.</p><p>^b Proportion recaptured = number of recaptured breeding adults / (number of recaptured breeding adults + number of new-captured breeding adults).</p><p>^c Sex ratio = number of breeding males / (number of breeding males + number of breeding females).</p><p>^d Some pools did not dry in some years. To facilitate analyses, we assigned such pools a late-fall hydroperiod end date. Mean hydroperiod was calculated using the capped end dates.</p><p>Population parameters represent actively breeding adults only.</p

Number of breeding spotted salamanders by experimental forestry treatment and mean pool hydroperiod.

<p>Shown for populations at 11 natural ephemeral pools in east-central Maine, USA. Treatments were: reference (uncut), 100m undisturbed buffer, 30m undisturbed buffer.</p

Mean (±1SE) size of breeding male spotted salamanders at 11 vernal pools in east-central Maine, USA.

<p>A) Body condition index (BCI) of recaptured males across three experimental forestry treatments and B) body mass (g) of new-captured males by forestry treatment and study year. Treatments were: reference (uncut), 100m undisturbed buffer, and 30m undisturbed buffer.</p

Breeding spotted salamander and wood frog abundance.

<p>Shown for populations at 11 natural ephemeral pools in east-central Maine, USA, across the six study years. Each pool is labeled with an identifying number and the applied forestry treatment. Experimental forestry treatments were: reference (uncut), 100m undisturbed buffer, 30m undisturbed buffer.</p