Climate variability, fire, vegetation recovery, and watershed hydrology
| Authors: | Thomas Meixner, Pete M. Wohlgemuth |
| Year: | 2003 |
| Type: | Paper |
| Station: | Pacific Southwest Research Station |
| Source: | First Interagency Conference on Research in the Watersheds, October 27-30, 2003. Washington, DC: U.S. Department of Agriculture, Agricultural Research Service: 651-656. |
Abstract
The San Dimas Experimental Forest was established in 1934. A large database of fire history, and stream flow exists for several locations within the forest. San Dimas was selected as a perfect example of the hydrology, geology, and ecology of the mountains of southern California. As such the long-term data set provides the best examples available of rainfallrunoff relationships in a mountainous Mediterranean climate. One of the most important ecological processes operating at San Dimas is the frequent stand replacing fires that occur approximately every 40 years. The effect of fire on streamflow is a pertinent topic considering the current national discussion about changes in fire policy in the western United States. The data sets at San Dimas provide an opportunity to investigate what the short and long term impacts of fire are on water resources in chaparral ecosystems. In particular the fires of 1938 and 1960 provide an opportunity to investigate the effect of fire on streamflow response. Immediately after the fires the well-known fire-flood response of chaparral watersheds is noted with extremely large flood peaks possibly due to the combined effects of removal of vegetation and litter by fire as well as the presence of hydrophobic soils. However longer term impacts of fire are noticeable, lasting as long as 20 years and are most likely related to aggrading vegetation coverage and the linked increase in evapotranspiration. Around 1960 several watersheds were type converted to annual and perennial grasslands from their native chaparral, this increased streamflow to the present day and offers insight into the importance of deeply rooted vegetation on summer streamflow in seasonally dry climates.