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Impacts of partial-retention harvesting with no buffer on the thermal regime of a headwater stream and its riparian zone Guenther, Steven Martin

Abstract

The temperatures of stream water and the stream bed influence biogeochemical processes and the growth and distribution of fish and macro-invertebrate species in streams. While numerous studies have examined the effects of various harvesting practices on stream temperature, none has estimated the effects on bed temperature, or conducted heat budget analysis before and after harvest to assess the mechanisms that control the magnitude of post-harvest stream heating. In this study, we analyzed data from a paired-catchment experiment involving both control and treatment streams and pre- and post-harvest monitoring. The partial retention harvesting resulted in removal of 50% of the basal area along 300 m of the channel in the treatment catchment. Stream temperature, bed temperature, riparian microclimate and stream hydrology were monitored in the treatment stream both before and after harvest. Daily maximum stream temperatures increased by up to over 7 °C during summer. Effects on winter temperatures were relatively small. Summer bed temperatures increased by as much as 6 °C, with greatest warming in areas of down-welling flow into the stream bed. Heat budgets were estimated for two reaches of a headwater stream before and after partial retention harvesting. Heat budget components responded in variable ways to the logging treatment depending on the reach, date, and weather. Incoming solar radiation was the largest input of energy into the stream following harvesting, while latent heat, hyporheic heat, groundwater heat, and bed heat exchanges tended to reduce the amount of daytime stream heating after harvest. These results will assist in understanding and predicting the spatial and temporal variability in stream temperature response to forest harvesting.

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