Negative trade-off between changes in vegetation water use and infiltration recovery after reforesting degraded pasture land in the Nepalese Lesser Himalaya
This work investigates the trade-off between increases in vegetation water use and rain water infiltration afforded by soil improvement after reforesting severely degraded grassland in the Lesser Himalaya of central Nepal. The hillslope hydrological functioning (surface and subsurface soil hydrauli...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-12-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | http://www.hydrol-earth-syst-sci.net/18/4933/2014/hess-18-4933-2014.pdf |
| Summary: | This work investigates the trade-off between increases in vegetation water
use and rain water infiltration afforded by soil improvement after
reforesting severely degraded grassland in the Lesser Himalaya of central
Nepal. The hillslope hydrological functioning (surface and subsurface
soil hydraulic conductivities and overland flow generation) and the
evapotranspiration (rainfall interception and transpiration) of the
following contrasting vegetation types were quantified and examined in
detail: (i) a nearly undisturbed, natural broadleaved forest; (ii) a
25-year-old, intensively-used pine plantation; and (iii) a highly degraded
pasture. Planting pines increased vegetation water use relative to the
pasture and natural forest situation by 355 and 55 mm year<sup>−1</sup>,
respectively. On balance, the limited amount of extra infiltration afforded
by the pine plantation relative to the pasture (only 90 mm year<sup>−1</sup> due to
continued soil degradation associated with regular harvesting of litter and
understory vegetation in the plantation) proved insufficient to compensate
the higher water use of the pines. As such, observed declines in dry season
flows in the study area are thought to mainly reflect the higher water use
of the pines although the effect could be moderated by better forest and
soil management promoting infiltration. In contrast, a comparison of the
water use of the natural forest and degraded pasture suggests that replacing
the latter by (mature) broadleaved forest would (ultimately) have a
near-neutral effect on dry season flows as the approximate gains in
infiltration and evaporative losses were very similar (ca. 300 mm year<sup>−1</sup>
each). The results of the present study underscore the need for proper
forest management for optimum hydrological functioning as well as the
importance of protecting the remaining natural forests in the region. |
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| ISSN: | 1027-5606 1607-7938 |