Influence of Livestock Grazing Strategies on Riparian Response to Wildfire in Northern Nevada

K. N. Dalldorf, S. R. Swanson, D. F. Kozlowski, K. M. Schmidt, R. S. Shane, G. Fernandez

Abstract


In 1999–2001 wildfires burned 1.13 million ha across northern Nevada, burning through many grazed riparian areas. With
increases in wildfire frequency and extent predicted throughout the Great Basin, an understanding of the interactive effects of
wildfire, livestock grazing, and natural hydrologic characteristics is critical. A comparison of pre- and postfire stream surveys
provided a unique opportunity to statistically assess changes in stream survey attributes at 43 burned and 38 unburned streams.
Livestock grazing variables derived from an extensive federal grazing allotment inventory were used to identify interactive
effects of grazing strategies, fire, and natural stressors across 81 independent riparian areas. Differences between baseline and
‘‘postfire’’ stream survey attributes were evaluated for significance using the nonparametric Mann–Whitney test for paired data.
Binary logistic regression models evaluated the influence of fire, grazing, and hydrologic characteristics on observed stream
survey attribute changes. Grazing attributes contributed most significantly to the bankfull width increase and bank stability
rating decrease models. The odds of bankfull width degradation (increase in bankfull width) decreased where there had been
rest is some recent years compared to continuous grazing. As the number of days grazed during the growing season increased,
the odds of bank stability degradation also increased. The occurrence of fire was not significant in any model. Variation in the
riparian width model was attributed primarily to hydrologic characteristics, not grazing. For the models in which grazing
variables played a role, stream survey attributes were more likely to improve over time when coupled with a history of
rotational grazing and limited duration of use during the growing season. This supports long-term riparian functional recovery
through application of riparian complementary grazing strategies.

Key Words: grazing history, Great Basin, logistic regression, stream survey


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