Quantifying Expected Ecological Response to Natural Resource
Legislation: a Case Study of Riparian Buffers, Aquatic Habitat, and
Trout Populations. K.L. Jones, G.C. Poole, J.L. Meyer, W. Bumback and E.A. Kramer. Ecology and Society. 11 (2): 15. 2006.
Regulations governing the management of streamside vegetation
(riparian buffers) lie at a nexus between environmental, social, and
land development interests, and can yield especially contentious
debates among stakeholders. In 2001, the State Legislature of Georgia,
USA, took up this debate; the Legislature reduced the minimum width of
mandatory-forested riparian buffers along designated trout streams from
~30 m (100 ft) to ~15 m (50 ft), and commissioned this study to assess
the expected response of existing trout populations. Because our
research was designed to provide rigorous and accessible data for
informing this management debate, this research may serve as a general
template for other studies designed to inform regulatory and management
decisions. We established and quantified relationships among riparian
forests, aquatic habitat (stream temperature and riffle embeddedness),
and trout reproductive success (biomass of young trout). We used these
relationships to determine the expected impacts of the buffer width
reduction on aquatic habitat and trout reproductive success at the
stream segment and stream network scales, and assessed associated
uncertainty. When compared with stream segments having 30-m wide
buffers, our analysis indicated that individual stream segments with
15-m wide buffers have: 1) higher peak temperatures (average peak
stream temperatures during the warmest week of the year increase by
~2.0 ± 0.3°C, depending on summertime climate conditions); and 2) more
fine sediments (fines in riffle habitats increase by approximately 25%
of the observed inter-study-site range). The data show that trout
populations will respond markedly to these habitat changes. Linear
regression models and an associated Monte Carlo uncertainty assessment
document an expected 87% reduction in young trout biomass, with a 95%
confidence interval ranging from a 66% reduction to a 97% reduction. A
landscape assessment showed that 63% of Georgia’s 2nd- to 5th-order
trout stream segments could maintain stream temperatures likely
(>50% probability) to support young trout in streams bordered by
30-m wide forested riparian buffers. Less than 9% of those streams
(only those at the highest elevations) would maintain such temperatures
with 15-m wide riparian buffers. As young trout are indicative of trout
reproductive success, our results portend substantial reductions or
elimination of trout populations in northern Georgia streams where
vegetated riparian buffer widths are reduced to 15 m.
Full text of Jones et al. 2006 at ecologyandsociety.org
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