Diversity without complementarity threatens vegetation patterns in arid lands

Abstract

Patterns found in mixed communities including grass, shrubs and trees function as natural water-harvesting systems in arid and\ud semi-arid regions throughout the world. Furthermore, self-organizing vegetation patterns may be indicators of environmental shifts in climate and land use change scenarios. Therefore, net facilitation, leading to resource concentration within vegetation patches, should be imitated and preserved.\ud This study analyses the ecological feedback between niche adaptation of similar band-forming species, and the environment in which species thrive. A minimal model for two coexisting species and the soil moisture balance was formulated to improve our understanding of the effects of species differentiation on the dynamics of plants and resources on single pattern and landscape scales. The model outcomes suggest that pattern-forming-species communities arise as a result of niche differentiation (driven e.g. by evolutionary changes), whereas similar adaptation strategies to cope with harsh conditions may lead to impoverishment of\ud environmental resources and loss of vegetation cover and diversity

Connectivity of Niches of Adaptation Affects Vegetation Structure and Density in Self‐Organized (Dis‐Connected) Vegetation Patterns

“…The tiger bush evolution under species differentiation is simulated by 2 SM , a model which describes the dynamics of soil moisture and two plant species, with biomass density n 1 and n 2 , over a 1D domain. The non‐dimensional form of 2 SM (Ursino & Callegaro, ) is:…”

“…The second right‐hand term accounts for soil moisture losses due to evaporation and leakage, and is modeled as a linear function of w itself. The transpiration rate has a linear dependence on soil moisture availability w and a quadratic dependence on local biomass density (Klausmeier, ) to simulate inter‐ and intra‐specific facilitation (Ursino & Callegaro, ). Water advection with constant and uniform velocity v is taken into account by the last term (Klausmeier, ; Ursino, ).…”

“…In the simulations, each species positively affects the other species growth, leading to intraspecific facilitation. The growth rate functions f 1 and f 2 are (Ursino & Callegaro, ): …”

“…Recent studies suggest that when species are grown in mixed environments, they tend to develop a greater trait differentiation than when they are grown in a monoculture (Tilman & Snell-Rood, 2014;Zuppinger-Dingley et al, 2014). Differentiation of plant species growing in a tiger bush is determinant for the ecosystem structure (Ursino & Callegaro, 2016a) and productivity (Ursino & Callegaro, 2016b) and indicates that hydrology needs to be considered as a biodiversity driver (Kornar et al, 2013).…”

Metastability as a Coexistence Mechanism in a Model for Dryland Vegetation Patterns

“…However, vegetation patches often consist of a mix of herbaceous and woody species, where the latter can usually be found in the centre of a patch, surrounded by the former [18,62]. Previous simulation-based studies of dryland ecosystem models have indeed been able to reproduce patterns in which two species coexist by considering a variety of different mechanisms and feedbacks that enable diversity in ecosystems [25,47,87,11,7]. One such facilitative mechanism occurs in a system of two species in which only one plant type induces a pattern forming feedback.…”