Local facilitation, bistability and transitions in arid ecosystems

Kéfi, Sonia; Rietkerk, Max; Baalen, Minus van; Loreau, Michel

doi:10.1016/j.tpb.2006.09.003

Cited by 172 publications

(253 citation statements)

References 58 publications

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“…The aridity level was estimated by b, the probability of recruitment of a new vegetation cell in a system without competition. We used the correlation approximation 26 to get numerically derived bifurcation diagrams, using the CONTENT software 3,27 . Along the transitions, we numerically determined the value of the bifurcation parameter at which the best-fitted model switches from power law to truncated power law.…”

Section: Methods Summarymentioning

confidence: 99%

“…We modelled grazing pressure as a higher mortality of {1}-cells. We used the correlation approximation 26 to analyse our model 3 . This method allowed the numerical derivation of bifurcation diagrams with the software CONTENT 3,27 .…”

Section: Methodsmentioning

confidence: 99%

“…Discontinuous transitions are abrupt, irreversible and among the most catastrophic changes of ecosystems identified 1 . For terrestrial ecosystems, it has been hypothesized that vegetation patchiness could be used as a signature of imminent transitions 3,4 . Here, we analyse how vegetation patchiness changes in arid ecosystems with different grazing pressures, using both field data and a modelling approach.…”

mentioning

confidence: 99%

“…Local facilitation is the biophysical ameliorative effect of sessile organisms, such as plants, on their neighbouring environment. Such local positive interactions induce vegetation patchiness 6,7,10 and determine the response of this patchiness to environmental change 3 .…”

mentioning

confidence: 99%

“…High grazing pressure pushes arid ecosystems towards the edge of extinction 1 . Increased aridity can then lead to desertification in a discontinuous way, where the possibility of recovery will be low [2][3][4]14 . How the consistent deviations from power laws exactly relate to desertification in the field is an important and urgent question for future research, because our model results suggest that such deviations may be early warning signals for desertification of arid ecosystems.…”

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confidence: 99%

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Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Kéfi

Rietkerk

Alados³

et al. 2007

Nature

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868

852

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Humans and climate affect ecosystems and their services 1 , which may involve continuous and discontinuous transitions from one stable state to another 2 . Discontinuous transitions are abrupt, irreversible and among the most catastrophic changes of ecosystems identified 1 . For terrestrial ecosystems, it has been hypothesized that vegetation patchiness could be used as a signature of imminent transitions 3,4 . Here, we analyse how vegetation patchiness changes in arid ecosystems with different grazing pressures, using both field data and a modelling approach. In the modelling approach, we extrapolated our analysis to even higher grazing pressures to investigate the vegetation patchiness when desertification is imminent. In three arid Mediterranean ecosystems in Spain, Greece and Morocco, we found that the patch-size distribution of the vegetation follows a power law. Using a stochastic cellular automaton model, we show that local positive interactions among plants can explain such power-law distributions. Furthermore, with increasing grazing pressure, the field data revealed consistent deviations from power laws. Increased grazing pressure leads to similar deviations in the model. When grazing was further increased in the model, we found that these deviations always and only occurred close to transition to desert, independent of the type of transition, and regardless of the vegetation cover. Therefore, we propose that patch-size distributions may be a warning signal for the onset of desertification.It is of the utmost importance to find early warning signals of transitions that can alter ecosystems' services in fundamental ways, causing losses of ecological and economic resources 2,4 . Determining proximity to transitions is especially important for arid ecosystems, which may convert into deserts 2,4,5 . According to the Millennium Ecosystem Assessment, increasing external pressures by human activities or climate change will lead to desertification, affecting the livelihood of more than 25% of the world's population 1 . A mechanism playing a dominant role in the functioning of arid ecosystems is local facilitation among plants [6][7][8][9] . Local facilitation is the biophysical ameliorative effect of sessile organisms, such as plants, on their neighbouring environment. Such local positive interactions induce vegetation patchiness 6,7,10 and determine the response of this patchiness to environmental change 3 .We investigated how the spatial organization of vegetation is influenced by the degree of external stress by combining modelling and field data from three grazed Mediterranean arid ecosystems in Spain, Greece and Morocco. In each of these ecosystems, we collected data on three sites that differed with respect to the livestock grazing pressure (Table 1; Methods). In each of the nine (3 3 3) sites, we analysed the number and the sizes of the vegetation patches (see Methods), and plotted the number of patches, N(S), as a function of their sizes, S. We fitted these patch-size distributions to two different mod...

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Section: Methods Summarymentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

mentioning

confidence: 99%

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confidence: 99%

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Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Kéfi

Rietkerk

Alados³

et al. 2007

Nature

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868

852

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Habitat loss‐induced tipping points in metapopulations with facilitation

2019

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Habitat loss is known to pervade extinction thresholds in metapopulations. Such thresholds result from a loss of stability that can eventually lead to collapse. Several models have been developed to understand the nature of these transitions and how they are affected by the locality of interactions, fluctuations or external drivers. Most models consider the impact of grazing or aridity as a control parameter that can trigger sudden shifts, once critical values are reached. Others explore instead the role played by habitat loss and fragmentation. Here we consider a minimal model incorporating facilitation between the individuals of the same species along with habitat destruction, with the aim of understanding how local cooperation and habitat loss interact with each other. A mathematical model incorporating facilitation and habitat destruction is derived, along with a spatially explicit simulation model. It is found that a catastrophic shift is expected for increasing levels of habitat loss, but the bifurcation becomes continuous when dispersal is local. Under these conditions, spatial patchiness is found and the qualitative change from discontinuous to continuous results are in agreement with previous studies on ecological systems. Our results suggest that species exhibiting facilitation and displaying short‐range dispersal will be markedly more capable of avoiding catastrophic tipping points.

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Disturbance Impacts on Thermal Hot Spots and Hot Moments at the Peatland‐Atmosphere Interface

Leonard

Kettridge

Devito

et al. 2018

Geophysical Research Letters

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Soil‐surface temperature acts as a master variable driving nonlinear terrestrial ecohydrological, biogeochemical, and micrometeorological processes, inducing short‐lived or spatially isolated extremes across heterogeneous landscape surfaces. However, subcanopy soil‐surface temperatures have been, to date, characterized through isolated, spatially discrete measurements. Using spatially complex forested northern peatlands as an exemplar ecosystem, we explore the high‐resolution spatiotemporal thermal behavior of this critical interface and its response to disturbances by using Fiber‐Optic Distributed Temperature Sensing. Soil‐surface thermal patterning was identified from 1.9 million temperature measurements under undisturbed, trees removed and vascular subcanopy removed conditions. Removing layers of the structurally diverse vegetation canopy not only increased mean temperatures but it shifted the spatial and temporal distribution, range, and longevity of thermal hot spots and hot moments. We argue that linking hot spots and/or hot moments with spatially variable ecosystem processes and feedbacks is key for predicting ecosystem function and resilience.

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Local facilitation, bistability and transitions in arid ecosystems

Cited by 172 publications

References 58 publications

Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Habitat loss‐induced tipping points in metapopulations with facilitation

Disturbance Impacts on Thermal Hot Spots and Hot Moments at the Peatland‐Atmosphere Interface

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