Measurement and modelling of evapotranspiration in three fynbos vegetation types

Abstract

Many studies have investigated the water relations of indigenous plants in the fynbos shrublands of the Cape, South Africa. These have mainly focused on understanding the mechanisms by which individual plant species respond to droughts, the frequency and severity of which is expected to increase due to climate change. However, comparatively little information exists on the dynamics of water use by indigenous plants in the region, and, in particular, how water use varies seasonally and between sites. In this study we determined water use by 3 fynbos vegetation types growing at 4 different sites, namely: (i) lowland Atlantis Sand Plain fynbos growing on deep sandy soils, (ii) Kogelberg Sandstone fynbos growing in a riparian zone on deep alluvial soils, (iii) dryland Kogelberg Sandstone fynbos growing on shallow sandy soils at a montane site, and (iv) alluvial Swartland fynbos growing in clayey soils. Evapotranspiration (ET) was quantified at each site during specific periods using a boundary layer scintillometer and energy balance system. A simple dual source model in which the stand ET was calculated as the algebraic sum of outputs from soil evaporation and transpiration sub-models was used to scale up the ET measurements to annual values. The data showed large differences in ET depending on site characteristics and on plant attributes. Dense stands of riparian Sandstone Fynbos had an annual ET of 1 460 mm which exceeded the reference ET of 1 346 mm. Dryland Sandstone Fynbos used only 551 mm of water per year while the Sand Plain Fynbos' annual ET was 1 031 mm, which was similar to the reference ET of 1 059 mm. We conclude that some indigenous plant species use large volumes of water which should be accounted for in, e.g., groundwater recharge estimates, and calculations of incremental water gains after clearing alien invasive plants, among other applications.

Energy partitioning and its controls over a heterogeneous semi‐arid shrubland ecosystem in the Lake Naivasha Basin, Kenya

“…For years 2013 and 2014 the annual evapotranspiration was approximately 20% and 9% less than the annual precipitation received respectively implying that at least 80% of annual precipitation returned back to the atmosphere through evapotranspiration. These evapotranspiration values were generally larger than those reported for a dryland sandstone ecosystem (551 mm yr À1 ) in Southern Africa (Dzikiti et al, 2014), a grassland ecosystem (271-517 mm yr À1 ) in Eastern cape, South…”

Biophysical controls of water vapour and energy fluxes: Towards the development of biome scale predictive models of evapotranspiration in the Albany Thicket, South Africa

“…This system was different from the present study site with rainfall >800 mm. However, the result was similar to the 3.3 mm observed by Jia et al (2016) in northern China but different from the 4.5-5 mm reported by Dzikiti, Jovanovic, Bugan, Israel, and Le Maitre (2014) in the Fynbos Biome in South…”

“…China but different from the 4.5-5 mm reported by Dzikiti, Jovanovic, Bugan, Israel, and Le Maitre (2014) …”

Comparison of two remote sensing models for estimating evapotranspiration: algorithm evaluation and application in seasonally arid ecosystems in South Africa

“…1). A detailed description of the site is given by Dzikiti et al (2014). The dominant vegetation type was the Swartland alluvial fynbos (Mucina and Rutherford, 2006) on deeper sandy soils interspersed with patches of Swartland shale renosterveld on more stony, shale-derived soils.…”