Role of soil in regulating runoff processes in Pine- and Oak-dominated headwater catchments of the Western Himalayas
Abstract
The traditional perception in the Western Himalayas is that Oak (Quercus spp.) forests provide the most effective water conservation. In contrast, Pine (Pinus roxburghii) forests are colonizers replacing Oak forests in large areas while consuming excessive water. We conducted field experiments in two forested microcatchments (< 100 hectares each), representing Pine- and Oak-dominated forests, to understand the controls on runoff generation and ecosystem services exerted by soils under both forests in the Western Himalayan headwaters.
The soil under the Pine forest was sandy loam of shallow depth, while that under the Oak forest was silty loam with deep soil profiles. The field capacity and residual moisture of soils under Pine (Oak) forests are 8% (34 %) and 4% (14%), respectively, corresponding to 0.33 bar and 15 bar soil water potential on the soil moisture characteristic curves constructed using the pressure plate experiment. Based on the water retention characteristics, we expect the Oak forests with deeper soils to behave like sponges with moisture stored in the soil profile during wet seasons and gradually released throughout the year to the streams. Observational evidence indicates this to be the case with the first-order streams draining the Pine forest drying up during the summer months while the streams in the Oak forest headwaters remain perennial. Measurement of field saturated hydraulic conductivity (Ksat) showed large spatial variability, yet consistently higher values in Pine forests (~24 cm d-1) as compared to Oak forests (~8 cm d-1). The high Ksat values in the Pine forest indicate that surface runoff under Pine stands will primarily be saturation-excess runoff during the wet season. The Oak forest with a large water holding capacity will take longer for soils to reach saturation, and runoff will be primarily by infiltration-excess. These findings have important implications for forest management policy in the Indian Himalayas in changing the narrative that forests primarily govern water flows. The evidence from this study highlights the role of other controls, for example, soils, in regulating runoff processes in forested headwater catchments.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H44H..02D