Assessing landscape structure and pattern fragmentation in semiarid ecosystems using patch-size distributions

Spatial vegetation patterns are recognized as sources of valuable information that can be used to infer the state and functionality of semiarid ecosystems, particularly in the context of both climate and land use change. Recent studies have suggested that the patch‐size distribution of vegetation in drylands can be described using power‐law metrics, and that these scale‐free distributions deviate from power‐law linearity with characteristic scale lengths under the effects of increasing aridity or human disturbance, providing an early sign of desertification. These findings have been questioned by several modeling approaches, which have identified the presence of characteristic scale lengths on the patch‐size distribution of semiarid periodic landscapes. We analyze the relationship between fragmentation of vegetation patterns and their patch‐size distributions in semiarid landscapes showing different degree of periodicity (i.e., banding). Our assessment is based on the study of vegetation patterns derived from remote sensing in a series of semiarid Australian Mulga shrublands subjected to different disturbance levels. We use the patch‐size probability density and cumulative probability distribution functions from both nondirectional and downslope analyses of the vegetation patterns. Our results indicate that the shape of the patch‐size distribution of vegetation changes with the methodology of analysis applied and specific landscape traits, breaking the universal applicability of the power‐law metrics. Characteristic scale lengths are detected in (quasi) periodic banded ecosystems when the methodology of analysis accounts for critical landscape anisotropies, using downslope transects in the direction of flow paths. In addition, a common signal of fragmentation is observed: the largest vegetation patches become increasingly less abundant under the effects of disturbance. This effect also explains deviations from power‐law behavior in disturbed vegetation which originally showed scale‐free patterns. Overall, our results emphasize the complexity of structure assessment in dryland ecosystems, while recognizing the usefulness of the patch‐size distribution of vegetation for monitoring semiarid ecosystems, especially through the cumulative probability distributions, which showed high sensitivity to fragmentation of the vegetation patterns. We suggest that preserving large vegetation patches is a critical task for the maintenance of the ecosystem structure and functionality

Ecogeomorphic coevolution of semiarid hillslopes: Emergence of banded and striped vegetation patterns through interaction of biotic and abiotic processes

[1] Nonlinear interactions between physical and biological factors give rise to the emergence of remarkable landform‐vegetation patterns. Patterns of vegetation and resource redistribution are linked to productivity and carrying capacity of the land. As a consequence, growing concern over ecosystem resilience to perturbations that could lead to irreversible land degradation imposes a pressing need for understanding the processes, nonlinear interactions, and feedbacks, leading to the coevolution of these patterns. For arid and semiarid regions, causes for concern have increased at a rapid pace during the last few decades due to growing anthropic and climatic pressures that have resulted in the degradation of numerous areas worldwide. This paper aims at improving our understanding of the ecogeomorphic evolution of landscape patterns in semiarid areas with a sparse biomass cover through a modeling approach. A coupled vegetation‐pattern formation and landform evolution model is used to study the coevolution of vegetation and topography over centennial timescales. Results show that self‐organized vegetation patterns strongly depend on feedbacks with coevolving landforms. The resulting patterns depend on the erosion rate and mechanism (dominance of either fluvial or diffusive processes), which are affected by biotic factors. Moreover, results show that ecohydrologic processes leading to banded pattern formation, when coupled with landform processes, can also lead to completely different patterns (stripes of vegetation along drainage lines) that are equally common in semiarid areas. These findings reinforce the importance of analyzing the coevolution of landforms and vegetation to improve our understanding of the patterns and structures found in nature

Grandes branquiópodos (Crustacea: Branchiopoda: Anostraca, Notostraca) en la provincia de Málaga (España) (año hidrológico 2012/2013)

Grans branquiòpodes (Crustacea, Branchiopoda: Anostraca, Notostraca) a la província de Màlaga, Espanya (any hidrològic 2012/2013) S'enumeren les cites d'una campanya de mostratge de grans branquiòpodes portada a terme a la província de Màlaga (Andalusia, sud d'Espanya) que ha permès la detecció de cinc espècies (Branchipus cortesi, Chirocephalus diaphanus, Streptocephalus torvicornis, Triops mauritanicus aggr. i Phallocryptus spinosa) en 90 masses d'aigua mostrejades.Large branchiopods (Crustacea, Branchiopoda, Anostraca, Notostraca) from Málaga province, Spain (2012/2013 hydrological year) This paper presents the occurrence of the large branchiopods detected during a survey carried out in the province of Málaga (Andalusia, southern Spain). Five species (Branchipus cortesi, Chirocephalus diaphanus, Streptocephalus torvicornis, Triops mauritanicus aggr. and Phallocryptus spinosa) were recorded at 90 sampled wetlands.Se enumeran las citas de una campaña de muestreo de grandes branquiópodos realizada en la provincia de Málaga (Andalucía, sur de España) que ha permitido la detección de cinco especies (Branchipus cortesi, Chirocephalus diaphanus, Streptocephalus torvicornis, Triops mauritanicus aggr. y Phallocryptus spinosa) en 90 masas de agua muestreadas

Hydrological heterogeneity in Mediterranean reclaimed slopes: runoff and sediment yield at the patch and slope scales along a gradient of overland flow

Hydrological heterogeneity is recognized as a fundamental ecosystem attribute in drylands controlling the flux of water and energy through landscapes. Therefore, mosaics of runoff and sediment source patches and sinks are frequently identified in these dry environments. There is a remarkable scarcity of studies about hydrological spatial heterogeneity in restored slopes, where ecological succession and overland flow are interacting. We conducted field research to study the hydrological role of patches and slopes along an "overland flow gradient" (gradient of overland flow routing through the slopes caused by different amounts of run-on coming from upslope) in three reclaimed mining slopes of Mediterranean-continental climate. We found that runoff generation and routing in non-rilled slopes showed a pattern of source and sink areas of runoff. Such hydrological microenvironments were associated with seven vegetation patches (characterized by plant community types and cover). Two types of sink patches were identified: shrub Genista scorpius patches could be considered as "deep sinks", while patches where the graminoids Brachypodium retusum and Lolium perenne dominate were classified as "surface sinks" or "runoff splays". A variety of source patches were also identified spanning from "extreme sources" (Medicago sativa patches; equivalent to bare soil) to "poor sources" (areas scattered by dwarf-shrubs of Thymus vulgaris or herbaceous tussocks of Dactylis glomerata). Finally, we identified the volume of overland flow routing along the slope as a major controlling factor of "hydrological diversity" (heterogeneity of hydrological behaviours quantified as Shannon diversity index): when overland flow increases at the slope scale hydrological diversity diminishes

Structural and functional control of surface-patch to hillslope runoff and sediment connectivity in Mediterranean dry reclaimed slope systems

Connectivity has emerged as a useful concept for exploring the movement of water and sediments between landscape locations and across spatial scales. In this study, we examine the structural and functional controls of surfacepatch to hillslope runoff and sediment connectivity in three Mediterranean dry reclaimed mining slope systems that have different long-term development levels of vegetation and rill networks. Structural connectivity was assessed using flow path analysis of coupled vegetation distribution and surface topography, providing field indicators of the extent to which surface patches that facilitate runoff and sediment production are physically linked to one another in the studied hillslopes. Functional connectivity was calculated using the ratio of patch-scale to hillslope-scale observations of runoff and sediment yield for 21 monitored hydrologically active rainfall events. The impact of the dynamic interactions between rainfall conditions and structural connectivity on functional connectivity were further analysed using general linear models with a backward model structure selection approach. Functional runoff connectivity during precipitation events was found to be dynamically controlled by antecedent precipitation conditions and rainfall intensity and strongly modulated by the structural connectivity of the slopes. On slopes without rills, both runoff and sediments for all events were largely redistributed within the analysed hillslopes, resulting in low functional connectivity. Sediment connectivity increased with rainfall intensity, particularly in the presence of rill networks where active incision under high-intensity storm conditions led to large non-linear increases in sediment yield from the surface-patch to the hillslope scales. Overall, our results demonstrate the usefulness of applying structuraland functional-connectivity metrics for practical applications and for assessing the complex links and controlling factors that regulate the transference of both surface water and sediments across different landscape scales

The Response of Badland Materials from Spain with Different Mineralogical Content on Seasonal Changes

Badlands are areas with limited vegetation, reduced or no human activity, and a great variety of geomorphic processes [1]. Badland materials have a different responsetothe same environmental conditions, because of differences in their mineralogical and physico-chemical characteristics. Many studies show that smectite-poorsediments are more resistant to different weathering treatments of freezing, thawing, wetting, and drying,than smectite-rich materials [2,3].In this paper, three unweathered samples of badlands from Spain were analyzed with the aim of monitoring, but also comparing physico-chemical changes caused by simulations of changes in climatic conditions. Selectedsediment samples havedifferent compositions. Besides quartz and calcite, the first sampleis composed of smectite and gypsum (3 UW), the second of smectite (4 UW), while the third sample is composed of neither smectite nor gypsum (5 UW). The experiment setup was designed in the way that each sample had three sub-samples, a sample for simulation of rain, snow, and a control sample (Figure 1). Sample_rain was treated with a rain intensity of ~850 ml/h for 10 minutes (~140 ml), while sample_snow was treated with crushed ice (~150 g). After precipitation simulations snow were put samples were placed in a climate chamber at - 3 °C together with a control sample. This was repeated for 15 cycles. Every cycle was documented with photographs. The leached solution was collected and its volume, pH, electrical conductivity (EC), and ion concentrations were measured. The second part of the experiment was based on exposing the samples after wetting to higher temperatures, 50 ° C. It was done in 8 cycles. FESEM and BET analyzes were performed for each sample before and after the experiments.The 3 UW samples had significantly different leachate pH and EC, while the leachate volume was similar for all samples during the experiment. Sulphate ions were leached in the highest concentrations during the whole experiment from the sample with both smectite and gypsum present. The sample with smectite has shown the highest disintegration of the structure, especially after the simulation of snow. The sample with smectite and gypsum has shown a lower degree of degradation than sample 3 UW due to the content of gypsum which increases the weathering resistance of the material. Sample 5 UW has shown the lowest degradation of the structure along with the weathering cycles. This study has proven that both mineralogical and physico-chemical properties of sediments are important for predicting their response to variable climate factors

Variations in hydrological connectivity of Australian semiarid landscapes indicate abrupt changes in rainfall-use efficiency of vegetation

[1] Dryland vegetation frequently shows self‐organized spatial patterns as mosaic‐like structures of sources (bare areas) and sinks (vegetation patches) of water runoff and sediments with variable interconnection. Good examples are banded landscapes displayed by Mulga in semiarid Australia, where the spatial organization of vegetation optimizes the redistribution and use of water (and other scarce resources) at the landscape scale. Disturbances can disrupt the spatial distribution of vegetation causing a substantial loss of water by increasing landscape hydrological connectivity and consequently, affecting ecosystem function (e.g., decreasing the rainfall‐use efficiency of the landscape). We analyze (i) connectivity trends obtained from coupled analysis of remotely sensed vegetation patterns and terrain elevations in several Mulga landscapes subjected to different levels of disturbance, and (ii) the rainfall‐use efficiency of these landscapes, exploring the relationship between rainfall and remotely sensed Normalized Difference Vegetation Index. Our analyses indicate that small reductions in the fractional cover of vegetation near a particular threshold can cause abrupt changes in ecosystem function, driven by large nonlinear increases in the length of the connected flowpaths. In addition, simulations with simple vegetation‐thinning algorithms show that these nonlinear changes are especially sensitive to the type of disturbance, suggesting that the amount of alterations that an ecosystem can absorb and still remain functional largely depends on disturbance type. In fact, selective thinning of the vegetation patches from their edges can cause a higher impact on the landscape hydrological connectivity than spatially random disturbances. These results highlight surface connectivity patterns as practical indicators for monitoring landscape health

Plot-scale effects on runoff and erosion along a slope degradation gradient

[1] In Earth and ecological sciences, an important, crosscutting issue is the relationship between scale and the processes of runoff and erosion. In drylands, understanding this relationship is critical for understanding ecosystem functionality and degradation processes. Recent work has suggested that the effects of scale may differ depending on the extent of degradation. To test this hypothesis, runoff and sediment yield were monitored during a hydrological year on 20 plots of various lengths (1–15 m). These plots were located on a series of five reclaimed mining slopes in a Mediterranean‐dry environment. The five slopes exhibited various degrees of vegetative cover and surface erosion. A general decrease of unit area runoff was observed with increasing plot scale for all slopes. Nevertheless, the amount of reinfiltrated runoff along each slope varied with the extent of degradation, being highest at the least degraded slope and vice versa. In other words, unit area runoff decreased the least on the most disturbed site as plot length increased. Unit area sediment yield declined with increasing plot length for the undisturbed and moderately disturbed sites, but it actually increased for the highly disturbed sites. The different scaling behavior of the most degraded slopes was especially clear under high‐intensity rainfall conditions, when flow concentration favored rill erosion. Our results confirm that in drylands, the effects of scale on runoff and erosion change with the extent of degradation, resulting in a substantial loss of soil and water from disturbed systems, which could reinforce the degradation process through feedback mechanisms with vegetation