The Contrasting Effects of Wildfire and Clearfelling on the Hydrology of a Small Catchment

Abstract

A wild®re in an aorested research catchment presented the rare opportunity to compare the hydrological eects of wild®re with the eects of clearfelling in the same catchment in the Jonkershoek Valley, in the south-western Western Cape Province of South Africa. The timber plantation, which occupies 57% of the 2 km 2 catchment, had been clearfelled and re-planted to Pinus radiata roughly ®ve years before the ®re. The eects of the two treatments on total¯ow, stormow and quick-¯ow volumes, peak discharge and storm response ratio were determined by means of multiple regression analysis, employing the dummy variable method to test for the signi®cance of treatments. Both clearfelling and wild®re caused signi®cant increases in all the stream-¯ow variables analysed. But the clearfelling eect was dominated by large increases in total¯ow (96% over three years), of which storm-¯ow and quick-¯ow volumes formed only minor parts. After the wild®re, by contrast, increases in total¯ow were small (12%) but the storm¯ow increases were three-to fourfold in the ®rst year and roughly double in the second year. The wild®re caused ®re-induced water repellency in the soils which led to overland¯ow on mid-slope sites, where soil in®ltrability normally far exceeds local rainfall intensities. It is argued that these results support the hypothesis that stream-¯ow generation processes were changed by the wild®re in that overland¯ow made a direct contribution to storm¯ows, but that clearfelling had no such eect.

FORMATION OF POST-FIRE WATER-REPELLENT LAYERS IN MONTERREY PINE (pinus radiata D. DON) PLANTATIONS IN SOUTH-CENTRAL CHILE

“…Similar results were reported by Scott (1997) in his study of a 5-year-old Monterrey pine plantation on sandy South African soils following clearcutting. Only a few studies have documented the duration of post-fire water repellent layers (DeBano, 2000b;Stropki et al, 2005;Erickson and White 2008).…”

Effects of land use change on streamflow and stream water quality of a coastal catchment

“…Increased runoff and reduced infiltration and soil water storage were also found by Scott (1997) and Scott et al (1998b) in other areas of the southwestern Cape with similar land use and catchment characteristics to the Touws. Le Maitre et al (2014) showed that simulation of clear-felling of pines and degrees of water repellency of soils after fires in invaded Acacia areas in a neighbouring catchment to the Touws River produced the same hydrological response.…”

Hydrological response of a small catchment burned by experimental fire

“…Increases in streamflow after fire have also been observed by others (Lavabre et al, 1993;Scott, 1993Scott, , 1997Seibert et al, 2010), and are often attributed to decreased canopy interception storage (e.g. Scott and Van Wyk, 1990).…”