This study was undertaken to determine the effect of vegetation structure (the ratio of
re-seeding to re-sprouting plants) on post-fire catchment water yield. Plant communities
are the only components of mountain catchments which can be manipulated to augment
water supplies on any practical scale. Burning, which is one of the options available to
catchment managers, reduces plant biomass and increases water yield by reducing
transpiration and interception losses.
Communities dominated by re-seeding species tend to recover more slowly after fires
than when sprouters predominate. The rate of vegetation recovery will determine the
rate at which streamflow returns to pre-fire levels. Sprouters may use more water than
seeders in the early post-fire period by virtue of their greater leaf area, which both
increases interception and transpiration losses. Leaf area development could be used as
a simple determinant of post-fire water yield if transpiration losses per unit leaf area are
similar in seedlings and sprouters.
In this study, a comparison was made of the transpiration rates of seedlings and sprouters
of Protea nitida after a fire in Swartboskloof (Cape Province) in 1987. Plant water
potentials were determined (index of the degree of stress) and leaf stomatal
conductances were measured.
Results indicate that transpiration rates are similar throughout the year except during the
short summer drought period when the seedlings have comparatively low transpiration
rates (< 1 mmo1 m-2 s-1 compared to 2-3 mmo1 m-2 s-1 of the sprouter), and
i
immediately after the first winter rains where the seedlings have comparatively high rates
(approxi.mately 4 mmol m-2 s-1 compared to 2 mmol m-2s-1.) The 1ow summer rates
are thought to be the result of drought stress induced by limited water supply and the
shallow root systems of the seedlings. The higher winter rates suggest that the shallow
surface roots of the seedlings respond quickly to increased surface moisture. Differences
in root structure (Le. shallow seedling roots and well-developed deep sprouter roots)
rather than regeneration mode appear to be responsible for the marginal differences
observed in transpiration rates. These differences are expected to disappear as seedling
roots develop and occupy the profile. Leaf area could therefore, be used as a
determinant of catchment water yield. / Thesis (M.Sc.)-University of Natal, 1990
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/8097 |
| Date | January 1990 |
| Creators | Smith, Rosemary Elizabeth. |
| Contributors | Pammenter, Norman W. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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