Toward an extreme world: The hyper‐arid ecosystem as a natural model

Abstract

The forecasted increased frequency and intensity of extreme climatic events may strongly affect ecosystem structure and function in the future. It is unclear how ecosystems will function in the long run over a large spatial scale under a new extreme water cycle. This open question calls for a conceptual framework as a fundamental basis for theoretical and experimental exploration of ecosystem function on a large scale driven by an extreme climate envelope. To assess the problem on a large scale, we investigated hyper‐arid ecosystems (HAEs) as natural tangible models that already function under an extreme climatic envelope. Our new assertion is that if extreme climate change drives arid lands to function under alternate extreme conditions, then arid land ecosystems will function like an HAE as an alternative state, rather than progress to desertification. To support our assertion, we developed a conceptual framework of HAEs that includes a geo‐hydrological “abiotic engine” that drives HAE function by soil moisture diversity and plant functional groups. Based on this conceptual framework, we suggest incorporating two new hypotheses in climate change studies to advance our understanding of responses of large‐scale, water‐limited ecosystems: (1) Hydro‐climatic extremes in water‐limited ecosystems will reduce the degree of resource conservation by slope ecosystems due to reduction in plant cover and soil. The decreased ecosystem function on the slope will be compensated for by increasing the effect of the abiotic engine on the ephemeral stream, thus enhancing meta‐ecosystem functioning in the ephemeral stream. (2) In water‐limited ecosystems, climate change toward hydro‐climatic extremes will rescale the dominant hydro‐ecological processes of pulse–reserve, source–sink, and connectivity along the semiarid, arid, and HA gradients in two ways: (i) shrinking of both spatial and temporal dimensions; and (ii) shrinking in the temporal dimension and expanding in the spatial dimensions. The first rescaling trajectory is related to biodiversity–ecosystem function and the second to the abiotic engine processes.

Assessment of Vegetation Dynamics at a Hyper Arid Region Using Remote Sensing, a Case Study from The Arava Valley

“…According to the aridity index [42], the area is defined as hyper-arid (aridity index values range between 1-2; Figure 1). In the hyper-arid region, as opposed to the arid or more humid environments, the vegetation grows only within the active ephemeral streams, and not under any morphological structure, to increase water availability [5,37] as can be seen in Figure 2.…”

“…Vegetation at the HAE, grows naturally only within active ephemeral cannels [5,37]. The data of the vegetation cover for both proxies was extracted only there.…”

“…While studies focusing on the rainfall trends of central and northern Israel have received much interest in the scientific literature [31,49,[74][75][76][77], very few studies have researched southern Israel and Jordan. This may be due to the natural variability of rainfall in the hyper-arid environment and the scarcity of meteorological stations, which makes it difficult to reach conclusive results [3,5]. Several studies have identified a decline in the amount of yearly rainfall in the Arava region in the last decades [28,30,78].…”

“…Drylands constitute about 40% of the world's land area, of which about a quarter are considered to be hyper-arid environments (HAE) with harsh climatic conditions [1]. Drylands are characterized by high inter-annual variability in rainfall [2,3], however, the variability and the uncertainty of rainfall events are much greater in the hyper-arid climate zone, and prolonged droughts occur more regularly [4][5][6][7]. To survive the high inter-annual climatic fluctuations, vegetation in arid environments has developed various mechanisms to survive, including flowering strategies, seed dormancy, germination when suitable environmental conditions occur, and many others [8].…”

Case studies associated with the 10 major geodiversity-related topics

“…More recently, the influence of geodiversity on biodiversity has become a very active field of research and is increasingly involving ecologists and multidisciplinary teams (e.g. [20][21][22][23][37][38][39][40][41][42][43][44][45][46]). The reason for this is that it is now recognized that biodiversity is strongly influenced by the physical environment [47].…”