Non rainfall moisture interception by dwarf succulents and their relative abundance in an inland arid South African ecosystem

Abstract

Dwarf succulents persist in the arid Succulent Karoo despite the low‐water storage capacities of their contracted leaves and stems that are inadequate for enduring severe and prolonged drought. We examined the contribution of non‐rainfall moisture (fog, dew, water vapour) to the water budgets and relative abundance of two endemic dwarf succulents Agyroderma pearsonii and Cephalophyllum spissum. Non‐rainfall moisture was measured with automated lysimeters containing bare quartz‐gravel soils and introduced A. pearsonii and C. spissum individuals at hourly intervals spanning an 8‐month wet winter to dry summer period. Total non‐rainfall atmospheric moisture intercepted by the bare quartz‐gravel substrate of 137·6 mm, of which water vapour adsorption contributed 56·2 mm, fog 78·2 mm and dew 3·4 mm, was virtually equivalent to the rainfall amount of 142·7 mm. Agyroderma pearsonii intercepted 228·4 mm of non‐rainfall moisture of which water vapour adsorption contributed 117·1 mm, fog 104·4 mm and dew 6·9 mm. This was nearly three times the non‐rainfall amount of 88·7 mm y−1 intercepted by C. spissum, of which water vapour contributed 44·3 mm, fog 41·3 mm and dew 3·1 mm. The greater quantity of non‐rainfall moisture intercepted by A. pearsonii corresponded with its threefold greater leaf abundance and twofold greater canopy cover than that of C. spissum. We conclude that non‐rainfall moisture, especially the absorption of atmospheric water vapour by soils and its uptake by the extensive network of superficial roots of dwarf quartz‐field succulents are vital in sustaining their growth and survival and in determining their distributions and relative abundance. Copyright © 2012 John Wiley & Sons, Ltd.

Partitioning of non rainfall water input regulated by soil cover type

“…Plant canopies are ideal dew and fog interceptors (Vogel and Müller-Doblies, 2011) and the excess of water harvested over the canopystorage capacity is transferred to the soil surface via stem flow or leaf drip where it is absorbed by the plant root system (Hutley et al, 1997). Also the adsorption of atmospheric water vapour by soils and its uptake by the superficial roots of plants are vital in sustaining their growth and survival and in determining their distributions and relative abundance in arid zones (Matimati et al, 2013). Similarly, our results point out a significant water supply by NRWI on plants, providing water on their surface and in the soil underneath.…”

Climate Change Impacts on Dwarf Succulents in Namibia as a Result of Changes in Fog and Relative Humidity

“…11). Overall, both genera of dwarf succulent show a significant loss in habitat and are negatively affected by the future climate changes especially as they rely heavily on non-rainfall moisture events such as fog, dew and water vapour [6]. The ability of these genera to migrate across the landscape and occupy newly suitable areas identified in this study is thought to be extremely limited, especially considering the timescale involved.…”

“…Previous studies have shown that the current distribution of Conophytum and Lithops is less dependent on rainfall and temperature, but instead relies more on non-rainfall moisture such as fog, dew, and water vapour [2,6]. Due to the general lack of other forms of non-rainfall data, in this study we used fog data, with the additional variable of relative humidity as climate variables.…”

Biodiversity and climate change: Risks to dwarf succulents in Southern Africa

“…Fog is recognised to be especially prevalent on the west coast and along some larger river systems, notably the Orange River. The contribution made by dew to annual precipitation appears to be less pronounced (<20-fold less), although it is much more widespread than the effects of fog (Matimati et al, 2013).…”

“…Rainfall declines east to west and south to north but is also characterised by its unpredictable nature. Non-rainfall moisture is thought to make a significant contribution to make a substantial, and reliable, contribution to total moisture availability (Matimati et al, 2013). Fog is recognised to be especially prevalent on the west coast and along some larger river systems, notably the Orange River.…”