Tree water potentials supporting an explanation for the occurrence of Vachellia erioloba in the Namib Desert (Namibia)

Abstract

Background: Site-vegetation relations of Vachellia erioloba, Faidherbia albida, Euclea pseudebenus and Tamarix usneoides in two contrasting locations in the Namib Desert (Namibia) were evaluated with the goal to relate soil water availability to the occurrence of trees under hyper-arid conditions. Methods: Plant water potentials were measured using a pressure chamber in the field. Pre-dawn water potentials were assessed to reflect the soil water potential of the rhizosphere. Midday water potentials were measured to assess the strongest negative water potential applied by the sample trees. Results: Pre-dawn water potentials and midday water potentials indicated access to soil water in the rhizosphere and by this, provide an explanation for an occurrence of V. erioloba within the extreme environmental conditions of sand dunes in the Namib Desert. Diurnal ranges seem to reflect more and less suitable stands, in terms of soil water availability, within the sampling sites. While the impact of the ephemeral Kuiseb river on soil water availability was assessed through the four species' plant-internal water relations, comparable pre-dawn water potentials of V. erioloba at both sites indicate soil water availability also in the dunes of Namibrand. The extreme midday water potentials of the dune plants possibly show the upper limit of tolerance for V. erioloba. Conclusions: The preliminary data provide an explanation of the occurrence and distribution of the investigated species in beds of ephemeral rivers and on dunes under the hyper-arid climatic conditions of the Namib Desert and qualify suitability within the assessed sites. Understanding the plant-physiological processes and assessing the plant-internal water potential provides a valuable tool to evaluate soil water availability within the rhizosphere and to describe an adaptation potential of investigated species. The comparability of pre-dawn water potentials at both sites indicates unexpected soil water availability within lower parts of the dunes of Namibrand. Further research needs are derived concerning the origin and distribution of such soil water. These species in these specific tree-environments are understudied and little published, thus the results support an improved understanding of the ecology in arid environments.

Underground deserts below fertility islands? – Woody species desiccate lower soil layers in sandy drylands

“…For instance, Bhark and Small (2003) showed that water infiltration rarely exceeds half a meter after rainy periods in woody–grassy mosaics of New Mexico, while Yang et al (2012) also found a lack of deep soil recharge in arid forest-steppes of the Chinese Loess Plateau. Nevertheless, large sandy regions with sparse tree cover and good soil infiltration capacity, such as the Namibrand in South Africa (Krug 2017), the Keerqin area in NE China (Zeng et al 2009), the Nebraska Sand Hills in North America (Adane et al 2018) or the Doñana sand dunes in Spain (Munoz-Reinoso and Novo 2005) may show soil moisture patterns similar to our findings.…”

Underground deserts below fertility islands? Woody species desiccate lower soil layers in sandy drylands

“…For instance, Bhark and Small () showed that water infiltration rarely exceeds half a meter after rainy periods in woody–grassy mosaics of New Mexico, while Yang et al () also found a lack of deep soil recharge in arid forest‐steppes of the Chinese Loess Plateau. Nevertheless, large sandy regions with sparse tree cover and good soil infiltration capacity, such as the Namibrand in South Africa (Krug ), the Keerqin area in NE China (Zeng et al ), the Nebraska Sand Hills in North America (Adane et al ) or the Doñana sand dunes in Spain (Munoz‐Reinoso and Novo ) may show soil moisture patterns similar to our findings.…”

Camelthorn and blackthorn trees provide important resources for Southern Pied Babblers (Turdoides bicolor) in the Kalahari

“…Camelthorns are the largest trees in the Kalahari, growing up to 16 m tall (Krug 2017) with canopy diameters up to 22 m (Carr 1976, Moustakas et al . 2006).…”