Patch- to hillslope-scale geodiversity: Implications for durability of dryland ecosystems under climatic changes

Geodiversity encompasses the natural heterogeneity of geologic, topographic, and pedogenic systems. It determines biodiversity and dictates a range of ecosystem services. Specifically, since geodiversity regulates hydrological connectivity and soil properties, it affects the soil-water dynamics. This feature is particularly relevant for drylands, where primary productivity is predominantly determined by soil-water availability. We present results and insights obtained in a set of recent and ongoing studies in shrublands of the semi-arid Negev region of southern Israel, revealing that hillslope-scale geodiversity dictates the vitality of shrubs. The region has experienced consecutive droughts and a substantial precipitation decrease over the past two decades. In high-geodiversity hillslopes – defined with a thin (~ 0.1 m thickness) and stony calcic xerosol layer that lies on highly-weathered calcareous bedrocks – shrubs are abundant, with high species richness and high vitality. At the same time, in low-geodiversity hillslopes, defined with a thick soil layer (> 1 m thickness) and no stoniness, shrubs are very sparse and dominated by one species (Noaea mucronata (Forssk.) Asch. & Schweinf.), of which the majority have not survived the recent prolonged droughts. These studies show that hillslope-scale geodiversity alleviates the water stress imposed on the shrubs, improving their durability under long-term droughts and climate change.

A complementary study that is currently being implemented along an aridity gradient (semi-arid, arid, and hyper-arid regions) in southern Israel reveals the substantial impact livestock trampling routes (also known as treading paths, livestock terracettes, cattle trails, migration tracks, cowtours, etc.) have on patch-scale geodiversity, consequently affecting geo-ecosystem functioning. Specifically, the extremely compacted routes minimize rainwater infiltration, thus increasing runoff-rainfall ratio. The generated runoff flows downslope, where it accumulates in shrubby patches. Thus, the shrubs experience higher soil-water availability, and are more resilient to drought episodes and climatic changes. The effect of the trampling routes is further amplified by accentuating the hillslopes’ characteristic ‘step-like profile’, which reduces hydrological connectivity at the hillslope scale, thus minimizes runoff leakage from the system. 

Note: the study is funded by the Israel Science Foundation (ISF), grant number 602/21.