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

Jessica Veysey Powell,Kimberly Babbitt

doi:10.3390/f8010010

Abstract

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).

Highlights

Pressure to manage forests for multiple uses is increasing globally as climate change progresses, and renewable energy demands, human populations, and per capita land consumption grow [1].Natural resource extraction and wildlife conservation are two uses that are frequently pitted against each other during inter-user discussions over forest management plans [2,3,4]
To assess the relative impacts of forestry treatment and hydroperiod on spotted salamander and wood frog eggmass abundance and metamorph SVL, and on wood frog metamorph abundance, we developed linear mixed-effects regression models (LME) using the “lme” function in S-Plus 8.0 (Insightful Corporation, Seattle, WA, USA, 2007)
Our results indicate that the negative effects of cutting on terrestrial adults were perpetuated in the aquatic environment in salamander, but not frog, eggmass abundance

Summary

Introduction

Natural resource extraction and wildlife conservation are two uses that are frequently pitted against each other during inter-user discussions over forest management plans [2,3,4]. Clearcuts are an effective timber harvest technique for diversifying the age structure of trees within forests and for creating habitat for wildlife species that specialize in young forest habitats, but there is evidence that clearcuts negatively impact most amphibian species (e.g., [5,6,7]). For wetland-dependent amphibians, forested buffers adjacent to wetlands hold promise as a simple technique for mitigating the impacts of clearcuts. In stream systems, where most manipulative buffer work has been conducted, riparian buffers have been successfully used to mitigate the effects of clearcuts on multiple stream-dependent amphibian species (e.g., [11,12,13]). While many stream-dependent amphibian species typically remain close to streams (i.e., within 100 m), some wetland-dependent amphibians regularly range hundreds of meters into the surrounding landscape and may respond very differently to buffers [16,17,18]

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Discussion

Conclusion