Global ecosystem thresholds driven by aridity

Abstract

Aridity, which is increasing worldwide because of climate change, affects the structure and functioning of dryland ecosystems. Whether aridification leads to gradual (versus abrupt) and systemic (versus specific) ecosystem changes is largely unknown. We investigated how 20 structural and functional ecosystem attributes respond to aridity in global drylands. Aridification led to systemic and abrupt changes in multiple ecosystem attributes. These changes occurred sequentially in three phases characterized by abrupt decays in plant productivity, soil fertility, and plant cover and richness at aridity values of 0.54, 0.7, and 0.8, respectively. More than 20% of the terrestrial surface will cross one or several of these thresholds by 2100, which calls for immediate actions to minimize the negative impacts of aridification on essential ecosystem services for the more than 2 billion people living in drylands.

Synthetic Biology for Terraformation: Lessons from Mars, Earth and the Microbiome

“…3). Those findings have been reported in several ecosystems, globally [10] and regionally [132], and attain nitrogen cycling rates [22,132], micronutrients [79], soil fauna [24,135], changes in the relative importance of erosive agents [95], soil aggregates stability and the relationship between soils and plants [11]. Presumably, those changes would involve also a drastic change in soil microorganisms, which are the main biotic agents driving and connecting soil nutrients and stocks [23] and contribute importantly to enhance soil stability and water capacity.…”

“…Because tipping points deeply modify the concept of risk (there is no linear decay response as some external variables change) a different approach is needed to deal with their nature. Finally, also at the ecosystem level, different studies conducted in the field suggest the incidence of abrupt transitions in the soil system along spatial gradients of increasing aridity [11]. In particular, at certain aridity levels, corresponding to the inter-fase between semiarid and arid ecosystems, some studies have reported an abrupt transition of soil functioning (soil Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 29 December 2019 doi:10.20944/preprints201912.0383.v1…”

Synthetic Biology for Terraformation Lessons from Mars, Earth, and the Microbiome

“…Because tipping points deeply modify the concept of risk (there is no linear decay response as some external variables change) a different approach is needed to deal with their nature. Finally, also at the ecosystem level, different studies conducted in the field suggest the incidence of abrupt transitions in the soil system along spatial gradients of increasing aridity [117]. In particular, at certain aridity levels, corresponding to the inter-fase between semiarid and arid ecosystems, some studies have reported an abrupt transition of soil functioning (soil fertility and nutrient turnover rates) which correspond to patterns that fit in a catastrophic shift behavior [118] (see Figure 3).…”

Habitat loss causes long transients in small trophic chains

“…Bistability: dynamical system with two stable equilibria. Classic ecological examples are shallow and eutrophic lakes [62,63], vegetated or desert states in semiarid ecosystems [28,30] (see also [64]). Globally asymptotically stable equilibrium point: equilibrium point that is stable and such that all orbits of the system converge to it.…”

“…Moreover, external pressures like grazing or deforestation have shown that for the same aridity levels two possibilities are possible, vegetated or desert [28,29]. In lower levels of aridity multiple ecosystems can be observed (savanna, forest, grasslands, and shrublands) but for some levels of aridity abrupt changes occur [30]. Furthermore, in the framework of systems biology, a tipping point driving populations to extinction has been recently described experimentally in yeast [31].…”