From nonequilibrium initial conditions to steady dryland vegetation patterns: How trajectories matter

Abstract

The multiscale nature of ecohydrological processes and feedbacks implies that vegetation patterns arising in water‐limited systems are directly linked to water redistribution processes occurring at much shorter timescales than vegetation growth. This in turn suggests that the initially available water in the system can play a role in determining the trajectory of the system, together with the well‐known role of the rainfall gradient. This work explores the role of initial hydrological conditions on vegetation dynamics and vegetation patterns. To do so, the HilleRisLambers–Rietkerk model was solved with different rainfall amounts and a large range of initial hydrological conditions spanning from near‐equilibrium to far‐from‐equilibrium conditions. The resulting vegetation patterns and ecohydrological signatures were quantitatively studied. The results show that not only do initial hydrological conditions play a role in the ecohydrological dynamics but also they can play a dominating one even resulting in divergent vegetation patterns that exhibit convergent mean‐field properties, including a new set of hybrid patterns. Our results highlight the relevance of assessing both global ecological and hydrological signatures and quantitatively assessing patterns to describe and understand system dynamics and in particular to determine if the systems are transient or steady. Furthermore, our analysis shows that the trajectories the system follows during its transient stages cannot be neglected to understand complex dependencies of the long‐term steady state to environmental factors and drivers.

Understanding the hydrological response of a headwater-dominated catchment by analysis of distributed surface–subsurface interactions

“…In terms of hydrograph analysis, the KGE is found to detect the discrepancy in the base flow better than the NSE, which is in agreement with the literature 58 . Depending on the aim of the study, it may be seen as beneficial that changes in connectivity do not affect the aggregated hydrograph, however, the correct representation of connectivity may be significant when modelling morphodynamics, ecological processes, or (bio) geochemistry 9,11,[65][66][67] . A promising development in linking distributed and aggregated hydrological responses is the use of stable water isotope-based modeling approaches [68][69][70] , which allow constructing a more precise relationship between spatiotemporal distributions and the hydrograph that can be directly supported by field measurements 71,72 .…”

“…Runoff formation and preferential flow paths are interlinked with other environmental processes 7 . For example, increased infiltration along preferential flow paths creates local pressure gradients, concentration gradients or depletion of soil moisture, biogeochemical hotspots 8 , and vegetation patterns in water-limited ecosystems 9 . Further, spatial dynamics of infiltration and exfiltration, controlled by the interactions between surface and subsurface, regulate the runoff generation and formation in the catchment itself.…”

Bridging ecology and physics: Australian fairy circles regenerate following model assumptions on ecohydrological feedbacks

“…More field studies are needed for a more complete validation of the mathematical models of FCs and to enable a more realistic parameterization. Especially investigating the time scales of pattern formation in this dryland deserves more research because such patterns may be very long lived and form over hundreds of years (Caviedes-Voullième & Hinz, 2020). In this way, mutual collaboration between empiricists and modellers, for example with backgrounds in physics and ecology, will lead to a deep understanding of multi-scale feedbacks in complex ecological systems.…”

Lateral Flow and Contributing Area Control Vegetation Cover in a Semiarid Environment

“…An important aspect of the SMC‐patch size relationship has emerged through the organization of vegetation into patterns of sparse patches of varying size, shape, and diversity, surrounded by bare soils (Tongway et al., 2001). Patch size patterns have been studied using mathematical models (Caviedes‐Voullième & Hinz, 2020; Yizhaq et al., 2014;) to quantify the role of initial hydrological conditions on vegetation dynamics and the resulting spatio‐temporal patterns of surface components. The assumption behind the patch size distribution index is that environments with more water resources (i.e., higher SMC values) support larger vegetation patch areas (Kefi et al., 2007).…”