Scale dependence and patch size distribution: clarifying patch patterns in Mediterranean drylands

Meloni, Fernando; Granzotti, Cristiano Roberto Fabri; Bautista, Susana; Martinêz, Alexandre Souto

doi:10.1002/ecs2.1690

Cited by 29 publications

(31 citation statements)

References 68 publications

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“…Real world analyses can sometimes misleadingly yield power-laws due to sampling artefacts [60] or misfitting [61][62][63]. Various ways in which patterns are misconstrued as power-laws have been discussed in detail in multiple other forums [61,64,65].…”

Section: Discussionmentioning

confidence: 99%

Patchiness and scale-free correlations: characterising criticality in ecosystems

Sankaran¹,

Majumder

Viswanathan

et al. 2017

Preprint

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A variety of ecosystems exhibit spatial clustering devoid of characteristic sizes, also known as scale-free clustering. In physics, scale-free behaviour is known to arise when a system is at a critical point, which occurs at the edge of two phases of matter. Scale-free clustering in physics therefore indicates that a system is not resilient. Spatial ecological studies, however, posit that scale-free clustering arises away from critical points and is therefore an indicator of robustness. This inconsistency is troubling. Here, we synthesize the literature on cluster-size distributions together with analyses of a spatial ecological model that incorporates local birth, death and positive feedbacks. We argue that scalefree clustering in real ecological systems is driven by strong positive feedbacks. Using the model, we demonstrate that power-law relations may occur far away from, near or at the critical point of ecosystem collapse depending on the strength of local positive feedbacks. We therefore infer that clustering patterns are unrelated to critical points of ecosystem collapse. Power-law clustering, instead, indicates a different critical point, called a percolation point, that signifies the onset of spanning clusters in a landscape.Finally, we show that a collapse or a regime shift in an ecosystem is characterized by the emergence of scale-free spatial correlations in the system, reflected in a scale-free powerspectrum. * sumithras@iisc.ac.in 1 All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

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Section: Discussionmentioning

confidence: 99%

Patchiness and scale-free correlations: characterising criticality in ecosystems

Sankaran¹,

Majumder

Viswanathan

et al. 2017

Preprint

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“…Empirical results mainly from Mediterranean drylands (MDL) support patch size distribution deviating from power laws, suggesting that terrain features are relevant. 11,23,24 As suggested in Meloni et al, 24 plant-plant and plant-environment interactions seem to work together to produce vegetation patterns in drylands. In fact, theoretical models 2 and recent data 25 show that ecological conditions affect the spatial structure of vegetation, with consequences for the ecosystem functionality.…”

Section: Introductionmentioning

confidence: 89%

Empirical evidence reveals the phase diagram of patch patterns in Mediterranean drylands

Meloni¹,

Nakamura²,

Granzotti³

et al. 2017

Preprint

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Drylands are important ecosystems with limited water resources, often subject to desertification. Their ecological activities depend on spatial patterns formed by local vegetation, but the relation with vegetation growth remains unclear. Using satellite images of a typical semiarid shrubland in Southern Spain, we gather vegetation data and argue that vegetation cover can be interpreted by means of a percolation process. We use a static analysis that compares patch statistics in different spatial scales to study the various patch patterns that occurs in drylands. Our results indicate three distinct phases in the overall vegetation cover range.The spatial patterns of vegetation are separated by a first-and a second-order phase transition, in three different spatial scales.We measure the corresponding critical exponents and determine novel relations between scaling exponents. The results reconcile conflicting views about vegetation patterns in drylands and demonstrate that different phase transitions coexist in the phase diagram of dry shrublands in Southern Spain. In addition, our preliminary test with a distinct dryland supports the hypothesis of universality classes to sort different drylands.

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“…), which has recently been subject to criticism (Meloni et al. ). The scaling exponent of the frequency distribution is a measure of the fractal dimension (Hausdorff et al.…”

Section: Methodsmentioning

confidence: 99%

“…Alpha-DFA is related to another index commonly used to evaluate vegetation spatial patterns: the cumulative distribution function of patch size (White et al 2008), which has recently been subject to criticism (Meloni et al 2017). The scaling exponent of the frequency distribution is a measure of the fractal dimension (Hausdorff et al 1997) and is inversely related to alpha-DFA (Appendix S2).…”

Section: Vegetation Sampling and Spatial Patternsmentioning

confidence: 99%

Plant–plant interactions scale up to produce vegetation spatial patterns: the influence of long‐ and short‐term process

et al. 2017

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Vegetation spatial patterns emerge in response to feedback interactions between organisms and their environment, because of the redistribution of water and nutrients around the plant canopy or as a consequence of facilitation/competition interactions at the plant level, even in the absence of pre‐existing substratum heterogeneities. It has been suggested that changes in vegetation spatial patterns are a signal of transition shift in ecosystems. Understanding the factors that lead to aggregated spatial patterns and control the transition to random distributions requires that environmental and species information is taken into account. In this study, we investigated the relative contributions of aridity (a long‐term process), to which vegetation is adapted, and the area covered by bare soil (short‐term process) to plant–plant associations and their contribution to aggregated spatial patterns. The study was conducted in a gradient of aridity ranging from that in subalpine grassland habitats in the Pyrenees and Sierra Nevada mountains to that in the semiarid steppes of Cabo de Gata and the middle Ebro Valley in Spain. We compared sites that differed in aridity and a geophysical feature (north‐ vs. south‐facing slope). We observed that the relative contribution of aridity and bare soil to plant–plant facilitation and vegetation aggregation differed in subalpine and semiarid areas. Facilitation in subalpine habitats had a marked effect on aggregated spatial patterns, while aridity contributed to disruption of these patterns. Conversely, in semiarid habitats, the disruption of aggregated patterns was mainly promoted by an increase in bare soil area rather than in aridity. In semiarid habitats, the higher level of stress on south‐facing slopes increased facilitation interactions relative to north‐facing slopes, although this did not enhance the persistence of aggregated spatial patterns. We conclude that the use of aggregated spatial patterns as an indicator of ecosystem shift must distinguish and separately take account of long‐term processes to which vegetation adapt, and short‐term process.

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Scale dependence and patch size distribution: clarifying patch patterns in Mediterranean drylands

Cited by 29 publications

References 68 publications

Patchiness and scale-free correlations: characterising criticality in ecosystems

Patchiness and scale-free correlations: characterising criticality in ecosystems

Empirical evidence reveals the phase diagram of patch patterns in Mediterranean drylands

Plant–plant interactions scale up to produce vegetation spatial patterns: the influence of long‐ and short‐term process

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