Effects of plantation forest clearfelling on stream temperatures in the Plynlimon experimental catchments, mid-Wales

摘要

Hourly stream temperatures monitored over 28months, which spanned a 3 month period of environmentally sensitive plot-scaleharvesting of 20 ha. (20%) of the Nant Tanllwyth catchment (0.89 km2)on the south side of the main stream in early 1996, resulted in a 0.58°C (p< 0.001) increase in monthly mean stream temperature. Over the same 28 monthexperimental period, there was no significant increase in the monthly mean airtemperature recorded at a nearby automatic weather station. Monthly meantemperatures are highest in July and August in the year before and the yearafter the clearfelling, and one of the main effects of the clearfelling was todecrease the difference between the monthly mean stream and air temperatures.Despite the air temperatures being cooler in the post-clearfelling year, thestream temperatures still showed an increase in the summer months. Monthly mean maximum stream temperatures, also highest in July and August in theyear before and the year after the clearfelling, showed a marked increase of7.0°C: in July and 5.3°C in August from the pre- to the post-clearfellingyears, while monthly mean minimum air temperatures actually showed a slightdecrease for the same months. The likely effects on stream fauna are discussed,as are suggestions for, and likely effects of, buffer strips alongside thestreams. style="line-height: 20px;">Keywords: stream temperature; air temperature; ground surface temperature; clearfelling; Plynlimon