Semi-arid Landscapes Research Articles

A coupled vegetation/sediment transport model for dryland environments

AbstractDryland regions are characterized by patchy vegetation, erodible surfaces, and erosive aeolian processes. Understanding how these constituent factors interact and shape landscape evolution is critical for managing potential environmental and anthropogenic impacts in drylands. However, modeling wind erosion on partially vegetated surfaces is a complex problem that has remained challenging for researchers. We present the new, coupled cellular automaton Vegetation and Sediment TrAnsport (ViSTA) model, which is designed to address fundamental questions about the development of arid and semiarid landscapes in a spatially explicit way. The technical aspects of the ViSTA model are described, including a new method for directly imposing oblique wind and transport directions onto a cell‐based domain. Verification tests for the model are reported, including stable state solutions, the impact of drought and fire stress, wake flow dynamics, temporal scaling issues, and the impact of feedbacks between sediment movement and vegetation growth on landscape morphology. The model is then used to simulate an equilibrium nebkha dune field, and the resultant bed forms are shown to have very similar size and spacing characteristics to nebkhas observed in the Skeleton Coast, Namibia. The ViSTA model is a versatile geomorphological tool that could be used to predict threshold‐related transitions in a range of dryland ecogeomorphic systems.

Stream power framework for predicting geomorphic change: The 2013 Colorado Front Range flood

The Colorado Front Range flood of September 2013 induced a diverse range of geomorphic changes along numerous stream corridors, providing an opportunity to assess responses to a large flood in a semiarid landscape. We defined six classes of geomorphic change related to peak unit stream power and valley confinement for 531 stream reaches over 226km, spanning a gradient of channel scales and slope. Geomorphic change was generally driven by erosion of channel margins in confined reaches and by a combination of deposition and erosion in unconfined reaches. The magnitude of geomorphic change typically increased with unit stream power (ω), with greater responses observed in unconfined channels. Cumulative logit modeling indicated that total stream power or unit stream power, unit stream power gradient, and valley confinement are significant predictors of geomorphic response for this flood event. Based on this dataset, thresholds for geomorphic adjustment were defined. For channel slopes<3%, we noted a credible potential for substantial channel widening with ω>230W/m2 (16lb/ft-s; at least 10% of the investigated sites experienced substantial channel widening) and a credible potential for avulsions, braiding, and loss of adjacent road embankments associated with ω>480W/m2 (33lb/ft-s; at least 10% of the investigated sites experienced such geomorphic change). Infrequent to numerous eroded banks were very likely with ω>700W/m2 (48lb/ft-s), with substantial channel widening or major geomorphic change shifting from credible to likely. Importantly, in reaches where there were large reductions in ω as the valley form shifted from confined to relatively unconfined, large amounts of deposition-induced, reach-scale geomorphic change occurred in some locations at relatively low ω. Additionally, alluvial channels with slopes>3% had greater resistance to geomorphic change, likely caused by armoring by larger bed material and increased flow resistance from enhanced bedforms. Finally, we describe how these results can potentially be used by practitioners for assessing the risk of geomorphic change when evaluating current or planned conditions.

Soilscape evolution of aeolian-dominated hillslopes during the Holocene: investigation of sediment transport mechanisms and climatic–anthropogenic drivers

Abstract. Here we study the soilscape (soil-landscape) evolution of a field site in the semiarid zone of Israel. This region, like similar regions around the world, was subject to intensive loess accumulation during the Pleistocene and early Holocene. Today, hillslopes in this region are dominated by exposed bedrock with deep loess depositions in the valleys and floodplains. The drivers and mechanism that led to this soilscape are unclear. Within this context, we use a soilscape evolution model (mARM5D) to study the potential mechanisms that led to this soilscape. We focus on advancing our conceptual understanding of the processes at the core of this soilscape evolution by studying the effects of fluvial and diffusive sediment transport mechanisms, and the potential effects of climatic and anthropogenic drivers. Our results show that, in our field site, dominated by aeolian soil development, hillslope fluvial sediment transport (e.g., surface wash and gullies) led to downslope thinning in soil, while diffusive transport (e.g., soil creep) led to deeper and more localized soil features at the lower sections of the hillslopes. The results suggest that, in this semiarid, aeolian-dominated and soil-depleted landscape, the top section of the hillslopes is dominated by diffusive transport and the bottom by fluvial transport. Temporal variability in environmental drivers had a considerable effect on soilscape evolution. Short but intensive changes during the late Holocene, imitating anthropogenic land use alterations, rapidly changed the site's soil distribution. This leads us to assume that this region's soil-depleted hillslopes are, at least in part, the result of anthropogenic drivers.

Water fluxes between inter-patches and vegetated mounds in flat semiarid landscapes

It has been assumed that bare soil (BS) inter-patches in semi arid spotted vegetation behave as sources of water to near vegetated soil (VS) patches. However, little evidence has been gained from direct measurements of overland and infiltration water fluxes between bare soil inter-patches and shrub mounds at a scale compatible with available high resolution imagery and hydrological modeling techniques. The objective of this study is to address the thin scale internal redistribution of water between BS inter-patches and vegetated mounds at relatively flat spotted semiarid landscapes. The relation between plant cover, topography and runoff was inspected with non-parametric association coefficients based on high resolution remotely sensed imagery, ground truth topographic elevation and spatial-explicit field data on potential runoff. Measurements of advective flows at the same spatial scale were carried out at micro-plots of BS and shrub mounds. Water fluxes between BS inter-patch and a shrub mound were simulated under varying typical Patagonian rainfall scenarios with an hydrological model. Results obtained revealed that the soil properties, infiltration and overland flow metrics at the mounds and inter-patches exhibit spatially and dynamic variable hydraulic properties. High micro-topographic roughness and depression storage thickened overland flow depth at VS patches. At BS inter-patches prevailing low slopes and depression storage were found to be important variables attenuating the surface runoff. At both rainfall scenarios simulated, the soil under the shrub mound accumulated more moisture (from direct rain) and reached saturation long before this occurred in BS nearby inter-patch area. Overland flow at the inter-patch was attenuated as it reached the border of the patch, diverging from the latter as it followed the (small) topographic gradient. The overland flow generated inside the vegetated mound was effectively retained at the typical Summer rainfall scenario; while several threads of runoff were routed outside the mound at the typical Winter rainfall scenario. The results here shown fail to detect: (a) enough runoff momentum that could route runon onto the vegetated mounds and (b) a contrast in infiltration rates between BS and the vegetated mound enough to lead to a free-surface gradient in ponded water that could inundate the mound.

Managing temporary streams and rivers as unique rather than second-class ecosystems

Temporary streams and rivers support biodiversity and provide valuable goods and services, especially in arid and semi-arid landscapes. However, temporary streams and rivers are being degraded at alarming rates owing to development, hydromorphological alteration, and disposal of waste water, among other stressors, and pressure will likely increase under global change. Here we propose that it is key to manage temporary streams and rivers as a unique ecohydrological type and not as a permanent waterway or a terrestrial ecosystem. Nevertheless, two challenges hinder this goal. First, data availability on intermittent low regimes and associated biotas is currently scarce. As a consequence, flow-ecology relationships in temporary waterways are largely unknown, and appropriate metrics to define and monitor their ecological status are missing. Second, the ecological and social values of temporary streams and rivers are often underestimated, being regarded as secondary ecosystems relative to permanent waterways. To conserve temporary streams and rivers, ecologists need to define them as unique ecosystems and conservation targets, and practitioners need to systematically collect biological and hydrological data in these ecosystems. Innovative approaches at the intersection of ecology, citizen science, and management, can also contribute to their management and conservation by: i) mapping them, ii) informing people about their ecological values, iii) safeguarding them from further human threats, iv) preserving their flow regime when managing reservoirs, wastewater treatment plants, and water abstraction activities, and v) restoring physically-degraded temporary reaches (e.g. due to gravel mining and off-road use) or reaches that have lost historical flows due to increasing drought severity, diversions, and groundwater overuse.

Afforestation of arid and semiarid ecosystems in Turkey

Sustainable management of arid and semiarid forests requires careful planning and implementation. Afforestation by planting and seeding is a fundamental tool for the establishment of new forests on barren landscapes and restoration of degraded forests in arid and semiarid ecosystems. In afforestation efforts, the consideration of site preparation, selection of species, seed source, and planting methods pose a number of ecological and economic challenges. Possessing one of the world's richest floras, Turkey suffered from heavy degradation during the last millennia. Some studies suggested that forests and steppes once covered 60%-70% and 10%-15% of the Anatolian landscape, respectively. Growing population, overgrazing, clearance for agriculture, fires, excessive timber harvesting, and misuse of lands led to a 26% reduction in the forest area. The Turkish Forest Service completed 2.3 million ha of afforestation and 1.2 ha of erosion control works, mostly in semiarid landscapes. This article presents an assessment of afforestation activities in the semiarid and arid regions of Turkey and is a review of the efforts exerted during the period 1945 to 2014.

The relationship between weather and reproduction of the Barn Owl Tyto alba in a semi-arid agricultural landscape in Israel_esi

The relationship between weather and reproduction of the Barn Owl Tyto alba in a semi-arid agricultural landscape in Israel_esi

Comparative Study among Different Semi-Empirical Models for Soil Salinity Prediction in an Arid Environment Using OLI Landsat-8 Data

Salt-affected soils, caused by natural or human activities, are a common environmental hazard in semi-arid and arid landscapes. Excess salts in soils affect plant growth and production, soil and water quality and, therefore, increase soil erosion and land degradation. This research investigates the performance of five different semi-empirical predictive models for soil salinity spatial distribution mapping in arid environment using OLI sensor image data. This is the first attempt to test remote sensing based semi-empirical salinity predictive models in this area: the Kingdom of Bahrain. To achieve our objectives, OLI data were standardized from the atmosphere interferences, the sensor radiometric drift, and the topographic and geometric distortions. Then, the five semi-empirical predictive models based on the Normalized Difference Salinity Index (NDSI), the Salinity Index-ASTER (SI-ASTER), the Salinity Index-1 (SI-1), the Soil Salinity and Sodicity Index-1 and Index-2 (SSSI-1 and SSSI-2), developed for slight and moderate salinity in agricultural land, were implemented and applied to OLI image data. For validation purposes, a fieldwork was organized and different important spots-locations representing different salinity levels were visited, photographed, and localized using an accurate GPS (σ ≤ ±30 cm). Based on this a priori knowledge of the soil salinity, six validation sites were selected to reflect non-saline, low, moderate, high and extreme salinity classes, descriptive statistics extracted from polygons and/or transects over these sites were used. The obtained results showed that the models based on NDSI, SI-1 and SI-ASTER all failed to detect salinity bounds for both extreme salinity (Sabkhah) and non-saline conditions. In Fact, NDSI and SI-ASTER gave respectively only 35% dS/m and 25% dS/m in extreme salinity validation site, while SI-1 and SI-ASTER indicated 38% dS/m and 39% dS/m in non-saline validation site. Therefore, these three models were deemed inadequate for the study site. However, both SSSI-1 and SSSI-2 allowed a detection of the previous salinity bounds and furthermore described similarly and correctly the urban-vegetation areas and the open-land areas. Their predicted EC is around 10% dS/m for non-saline urban soil, about 25% dS/m for low salinity urban-vegetation soil, approximately 30% to 75% dS/m, respectively, for moderate to high salinity soils. SSSI-2 based semi-empirical salinity models was able to differentiate the high salinity versus extreme salinity in areas where both exist and was very accurate to highlight the pure salt where SSSI-1 has reach saturation for both salinity classes. In conclusion, reliable salinity map was produced using the model based on SSSI-2 and OLI sensor data that allows a better characterization of the soil salinity problem in an Arid Environment.

Sustainability of Hillslopes in Semiarid Rangelands: Effects of Rock Fragments

Rock fragments (RFs) affect micro-environmental conditions in underlying and surrounding soil, and thereby stimulate abiotic and biotic processes that interact with the surrounding environment. Microenvironmental conditions are of great importance in arid and semiarid landscapes, where surfaces feature high percentages of RFs. On south-facing hillslopes in the northern Negev region of Israel, soil was sampled from beneath small, medium, and large RFs – i.e., 4-6, 8-10, and 13-16 cm, respectively – that lay on the surface or were partially embedded in the soil. Control samples were taken from nearby bare soil. Rock fragment characteristics affected various soil properties with differing intensities. Under large and medium RFs soil moisture contents were higher than under the small ones; and embedded RFs promoted higher moisture contents than those lying on top of the soil (designated as

Taphonomy of mammalian fossil bones from the debris-flow deposits of Somosaguas-North (Middle Miocene, Madrid Basin, Spain)

Debris-flow hosted assemblages dominated by mammalian remains are very scarce in the fossil record and few examples are reported. Herein we present a detailed taphonomic study of Somosaguas-North (Madrid Basin, Spain), a Middle Miocene mammalian-dominated site embedded in debris-flow deposits, in order to increase our knowledge of the mode of formation of fossiliferous assemblages in this depositional context. The assemblage includes 6592 large-mammal remains belonging to at least 10 different species. Fossils are found in matrix-supported, poorly-sorted coarse arkosic sandstones and fine conglomerates, which are interpreted as the result of successive debris-flow deposits. Breakage constitutes a pervasive taphonomic alteration in the bone assemblage; however, together with unidentifiable bone fragments, we also found complete to almost complete skeletal elements. Bone remains are isolated, a fact that is indicative of a time of exposure of the carcasses long enough to enable decay and complete disarticulation. There are no associations of elements belonging to the same individual, which suggests that, prior to or during debris-flow transport, bones were profusely dispersed. Based on the taphonomic evidence, we suggest that Somosaguas-North assemblage was formed by successive debris-flow transport and burial of pre-existing thanatocoenoses. Bones from those thanatocoenoses were modified by biostratinomic agents (trampling, weathering) in varying degrees depending on their time of exposure. Debris-flow transport produced further abrasion and breakage in collagen-depleted bones. Our results are congruent with an environmental context of semiarid landscapes presenting long arid periods and highly irregular hydrological seasonality. Finally, we compared the Somosaguas-North assemblage with other debris-flow hosted vertebrate assemblages. Although Somosaguas-North shares taphonomic features with some of these sites, it is not possible to define consistent and single taphonomic patterns for debris-flow assemblages, given the varied taphonomic histories of the remains prior to and during debris-flow transport.

Mobile acoustic transects detect more bat activity than stationary acoustic point counts in a semi-arid and agricultural landscape

Arid environments are characterized by resource pulses that cause spatio-temporal variability in species abundance, which can make population assessments difficult. Mobile acoustic methods may improve survey success by maximizing geographic extent, characterizing landscape distribution patterns, and improving encounter rates. Bats exemplify survey challenges in arid environments as they are highly mobile and aggregate around spatio-temporal resource hotspots. We compared bat detection success of stationary acoustic methods to that of mobile acoustic transects. In a semi-arid landscape, we recorded bat echolocation calls and compared three different sampling methods along the same 24 km route: a driven transect; a set of five, permanent ten-minute point counts; and a set of point counts at nightly randomized locations. The effect of method on the number of bat passes was analyzed using a bootstrapped generalized linear mixed effect model. The mean number of passes for the mobile method was 2.14 (CI: 1.45–2.99) and 0.98 (CI: 0.77–1.21) for the pooled stationary methods. We suggest that driven transects more effectively measure bat activity in arid and open landscapes. Testing of novel survey methods in arid environments is vital to conservation success as climate change increases the extent of these biomes and the variability of resource pulses.

Controls on soil carbon storage from topography and vegetation in a rocky, semi-arid landscapes

Soil properties can exhibit strong spatial variation, even at the small catchment scale. Especially soil carbon pools in semi-arid, mountainous areas are highly uncertain because bulk density and stoniness are very heterogeneous and rarely measured explicitly. The effect of topographic and vegetation variables, on stoniness, bulk density and soil carbon has been explored in a 2.7km2 watershed of Sierra Morena in south Spain. Soil core samples were collected from 67 locations at 6 depths up to 0,3m. Stoniness and bulk density were measured with standard methods, total organic carbon through elemental analysis. These soil properties were then used to calculate carbon stock and related to solar insolation, elevation, slope, curvature, TWI, TPI, SPI and NDVI. Stone content depends on slope, indicating the importance of water erosion on long-term soil development. Spatial distribution of bulk density was found to be highly random. By means of conventional statistical methods, with the help of a random forest method, solar radiation and NDVI proved to be the key variable controlling soil carbon distribution. Total soil organic carbon stocks were 4.38kgm−2 on average, with stocks about double as high on north versus south-facing slopes. These results confirm the importance of the coupled soil moisture and vegetation dynamics on the carbon balance in semi-arid ecosystems. However, validation of the random forest model showed that the different covariates only explained 18% of the variation in the dataset. Apparently, present-day landscape and vegetation properties are not sufficient to fully explain the full variability in the soil carbon stocks in this complex terrain under natural vegetation. This is attributed to a high spatial variability in bulk density and stoniness, key variables controlling carbon stocks. Future improvement of mechanistic soil formation models could help estimating these soil properties better.

The Photovoltaic Heat Island Effect: Larger solar power plants increase local temperatures

While photovoltaic (PV) renewable energy production has surged, concerns remain about whether or not PV power plants induce a “heat island” (PVHI) effect, much like the increase in ambient temperatures relative to wildlands generates an Urban Heat Island effect in cities. Transitions to PV plants alter the way that incoming energy is reflected back to the atmosphere or absorbed, stored, and reradiated because PV plants change the albedo, vegetation, and structure of the terrain. Prior work on the PVHI has been mostly theoretical or based upon simulated models. Furthermore, past empirical work has been limited in scope to a single biome. Because there are still large uncertainties surrounding the potential for a PHVI effect, we examined the PVHI empirically with experiments that spanned three biomes. We found temperatures over a PV plant were regularly 3–4 °C warmer than wildlands at night, which is in direct contrast to other studies based on models that suggested that PV systems should decrease ambient temperatures. Deducing the underlying cause and scale of the PVHI effect and identifying mitigation strategies are key in supporting decision-making regarding PV development, particularly in semiarid landscapes, which are among the most likely for large-scale PV installations.

Hyper-temporal remote sensing for digital soil mapping: Characterizing soil-vegetation response to climatic variability

Indices derived from remotely-sensed imagery are commonly used to predict soil properties with digital soil mapping (DSM) techniques. The use of images from single dates or a small number of dates is most common for DSM; however, selection of the appropriate images is complicated by temporal variability in land surface spectral properties. We argue that hyper-temporal remote sensing (RS) (i.e., hundreds of images) can provide novel insights into soil spatial variability by quantifying the temporal response of land surface spectral properties. This temporal response provides a spectral ‘fingerprint’ of the soil-vegetation relationship which is directly related to a range of soil properties. To evaluate the hyper-temporal RS approach, this study first reviewed and synthesized, within the context of temporal variability, previous research that has used RS imagery for DSM. Results from this analysis support the notion that temporal variability in RS spectra, as driven by soil and climate feedbacks, is an important predictor of soil variability. To explicitly evaluate this idea and to demonstrate the utility of the hyper-temporal approach, we present a case study in a semiarid landscape of southeastern Arizona, USA. In this case study surface soil texture and coarse fragment classes were predicted using a 28year time series of Landsat TM derived normalized difference vegetation index (NDVI) and modeled using support vector machine (SVM) classification, and results evaluated relative to more traditional RS approaches (e.g., mono-, bi-, and multi-temporal). Results from the case study show that SVM classification using hyper-temporal RS imagery was more effective in modeling both soil texture and coarse fragment classes relative to mono-, bi-, or multi-temporal RS, with classification accuracies of 67% and 62%, respectively. Short-term transitions between wet and dry periods (i.e., <6months) were the dominant drivers of vegetation spectral variability and corresponded to the general timing of significant RS scenes within in our SVM models, confirming the importance of spectral variability in predicting soil texture and coarse fragment classes. Results from the case study demonstrate the efficacy of the hyper-temporal RS approach in predicting soil properties and highlights how hyper-temporal RS can improve current methods of soil mapping efforts through its ability to characterize subtle changes in RS spectra relating to variation in soil properties.

Vagaries of Monsoon, Resilience of Society: Revisiting Nature of Socio-political Structures in Early-modern Rajasthan

Recent writings have questioned the conventional portrayal of nature as benevolent and suggested that vagaries of monsoon necessitated regular negotiations to ensure agrarian production at multiple levels especially during early modern times in the semi-arid and arid landscape of Rajasthan. It is generally assumed that most of the negotiations were carried out by the peasantry, and political apparatus was usually a mere spectator or at best provided relief during severe scarcity. This article argues that political authorities were accommodative in their attitude towards the implications of inherent dynamism of the physical environment. Therefore, if not by choice then definitely under compulsions of natural exigencies, the ruling elites were forced to make preventive interventions by extending support to the peasantry in their negotiations with the environment.

Revisiting the paper “Using radiometric surface temperature for surface energy flux estimation in Mediterranean drylands from a two-source perspective”

The recent paper by Morillas et al. [Morillas, L. et al. Using radiometric surface temperature for surface energy flux estimation in Mediterranean drylands from a two-source perspective, Remote Sens. Environ. 136, 234–246, 2013] evaluates the two-source model (TSM) of Norman et al. (1995) with revisions by Kustas and Norman (1999) over a semiarid tussock grassland site in southeastern Spain. The TSM - in its current incarnation, the two-source energy balance model (TSEB) - was applied to this landscape using ground-based infrared radiometer sensors to estimate both the composite surface radiometric temperature and component soil and canopy temperatures. Morillas et al. (2013) found the TSEB model substantially underestimated the sensible H (and overestimated the latent heat LE) fluxes. Using the same data set from Morillas et al. (2013), we were able to confirm their results. We also found energy transport and exchange behavior derived from primarily the observations themselves to differ significantly from a number of prior studies using land surface temperature for estimating heat fluxes with one-source modeling approaches in semi-arid landscapes. However, revisions to key vegetation inputs to TSEB and the soil resistance formulation resulted in a significant reduction in the bias and root mean square error (RMSE) between model output of H and LE and the measurements compared to the prior results from Morillas et al. (2013). These included more representative ground-based vegetation greenness and local leaf area index values as well as modifications to the coefficients of the soil resistance formulation to account for the very rough (rocky) soil surface conditions with a clumped canopy. This indicates that both limitations in remote estimates of biophysical indicators of the canopy at the site and the lack of adjustment in soil resistance formulation to account for site specific characteristics, contributed to the earlier findings of Morillas et al. (2013). This suggests further studies need to be conducted to reduce the uncertainties in the vegetation and land surface temperature input data in order to more accurately assess the effects of the transport exchange processes of this Mediterranean landscape on TSEB formulations.

Game mammals of the Caatinga biome

Mammals stand out among the main game animals of the world, being exploited by human beings for different ends, and being important for the subsistence of several communities. In semiarid environments, as in the Brazilian Caatinga biome, wild mammals have been exploited by the local human population, including endangered species. In this scenario, beyond biological research of the exploited animals, ethnozoological studies are important for supporting plans for the sustainable management and conservation strategies for the mammalian fauna of the semiarid landscape. This study aims to contribute to new research into the ethnomammalogy of this specific region. It provides a catalogue of the mammals and their ethnozoological importance, including a brief characterization of game mammals of the morphoclimatic domain of the Caatinga. The results show that at least 41 species of wild mammals interact with the population that lives in the semiarid region, as sources of products that can be used for the following purposes: food (31 species), medicinal (38 species), ornamental or decorative purposes (23 species), in magical/religious practices (31 species), and as pets (24 species). Twenty-five species are hunted because of concerns over personal safety or predation on livestock and pests. Among the recorded mammals, 13 (31.7%) are listed in some threatened category (Critically endangered, Endangered or Vulnerable). Hunting is one of the main factors contributing to this situation, which provides evidence that conservation strategies should consider the associated human needs, integrating cultural aspects of the local populations, and ecological aspects associated with the biodiversity of the region.

Caracterização histórico-ambiental da APA dunas e veredas do baixo-médio São Francisco (BA)

O presente artigo busca traçar a caracterização histórico-ambiental da APA Dunas e Veredas do Baixo-Médio São Francisco, objetivando discutir aspectos gerais dos campos de dunas quaternárias existentes no Brasil e especialmente na APA supracitada, além de trazer ao debate as tipologias de dunas encontradas na região, o processo histórico-social da área e os principais impactos antropogênicos existentes na área de estudo. As dunas situam-se na ecorregião Dunas do São Francisco, é de responsabilidade do Poder Público Estadual, por meio do Decreto n. 6.547 de 18 de julho de 1997 e possui uma área de 1.085.000,00 hectares. O processo de ocupação no Brasil é caracterizado por total ausência de planejamento e pela destruição massiva dos recursos naturais, representada pelos diversos biomas, causando assim, uma gama de problemas ambientais, como por exemplo, a extinção de fauna e flora, alterações climáticas locais, assoreamento de cursos d’água, erosão dos solos e fragilização de paleo-ecossistemas, a exemplo das dunas fluviais em estudo, que margeiam o rio São Francisco no Nordeste brasileiro, e está ameaça pela ação desenfreada da prática de agricultura, pastoreio, retirada indiscriminada de areais, turismo (des)planejado, construções imobiliárias e desconhecimento da sua relevância pelos ribeirinhos. Trata-se de uma pesquisa qualitativa, onde inicialmente postergou-se por uma análise bibliográfica sistemática e posteriormente, fez-se o trabalho de campo, fundamentando-se substancialmente na Teoria Ecodinâmica de Tricart (1977). Neste sentido, é urgente a intervenção ambiental e a execução de propostas de conservação destes paleoambientes, representativos das mudanças climáticas pretéritas e verdadeiro laboratório natural a céu aberto no cenário semiárido do Brasil.

Geomorphology as a first order control on the connectivity of riparian ecohydrology

Geomorphic controls on ecohydrological connections, while implicit in processes such as the derivation of transpired water from alluvial aquifers, have not been systematically investigated. In this article we test the hypothesis that geomorphic setting is an important control on groundwater-sourced riparian evapotranspiration (ET) through a statistical investigation of 30years of daily flow data, monthly precipitation data, and semimonthly satellite images at fourteen 1-km-long river reaches representing a range of geomorphic settings in the semiarid landscape of New Mexico, USA. We focus on correlations between vegetation greenness (as a surrogate for vigor and transpiration rates), interannual variability in flow and rainfall characteristics, and valley metrics such as width, slope, and concavity. Sites were considered individually and in groups based on classification as perennial or intermittent. Principal component analysis (PCA) was used to distill related metrics into significant, uncorrelated, interpretable, underlying variables. Components were interpreted in the same manner as a factor analysis and were found to include overall magnitude of greenness, within-summer variability of greenness, overall wetness, rain vs. flow dominance, snowmelt vs. monsoon dominance, and mountain vs. basin geomorphic setting, among others. To broadly test the hypothesis that geomorphology affects the relationship between wetness and greenness, best subset regressions were constructed for the full range of sites and groups using all wetness and geomorphic components as potential predictor variables and greenness metrics as response variables. From our analysis we draw two main conclusions: (1) including geomorphic parameters provides new information that is nonredundant with precipitation and flow parameters in predicting vegetation extent and vigor. The parameters, especially curvature, may indicate causal processes, such as increased soil moisture availability on concave surfaces with convergent flow paths, or they may provide correlative information on the groundwater setting (gaining vs. losing). (2) When considering groups of sites, the dominance of precipitation over stream flow in delivering moisture was a predictor of high greenness; but this was not the case for any individual sites. This indicates that while greener communities developed in sites with greater average precipitation, at any single site the vegetation was able to adapt to either local precipitation or streamflow delivery of moisture in a given year and only the magnitude of the moisture delivered affected vegetation vigor. These findings emphasize the versatility of riparian vegetation to utilize soil moisture in convergent geomorphic settings or wet time periods, moisture that may otherwise tend to evaporate.

Lagostomus maximus (Desmarest) (Rodentia, Chinchillidae), the extant plains vizcacha in the Late Pleistocene of Uruguay

Ubilla, M. & Rinderknecht, A., April 2016. Lagostomus maximus (Desmarest) (Rodentia, Chinchillidae), the extant plains vizcacha in the Late Pleistocene of Uruguay. Alcheringa 40, xxx–xxx. ISSN 0311-5518The extant plains vizcacha, Lagostomus maximus, is described from the Late Pleistocene (Dolores Formation) of Uruguay based on an almost complete articulated skeleton. It is compared with the nominally extinct Pleistocene species of the genus. An AMS 14C taxon-age is determined for L. maximus at 11 879 ± 95 years BP (cal. BP 13 898–13 941). Lagostomus maximus is absent from modern mammal communities in Uruguay, and no Holocene evidence is available. Because L. maximus exhibits remarkable sexual and ontogenetic dimorphism, we examined a range of juvenile, sub-adult and adult male and female specimens. It is not possible to differentiate the articulated Pleistocene fossil from sub-adult specimens of L. maximus based on this sample. Moreover, the skull characteristics, including a broad vertical ramus of the zygomatic arch, semi-circular temporal crest and short robust sagittal crest, most closely resemble extant female individuals. Molar size is non-predictive for ontogenetic stage or body mass because it reaches stability during early adulthood. Other fragmentary skull remains are herein assigned to L. sp. cf. L. maximus. Lagostomus cavifrons from the Pleistocene of Argentina is considered synonymous with L. maximus. Its character states concur with the range of intraspecific variability and it has been established on a young adult or adult male individual. Likewise, the other Argentinean Pleistocene species based on incomplete mandibles, L. angustidens, L. striatus, L. heterogenidens, L. egenus, L. minimus and L. debilis, concur with ontogenetic morphs and are here assigned to Lagostomus sp. The ecological preferences of extant L. maximus infer open arid or semi-arid landscapes for the latest Pleistocene of southern Uruguay. This hypothesis is reinforced by the coeval presence of Microcavia, Galea and small camelids in the same strata. The Last Glacial Maximum likely promoted this environmental setting. Latest Pleistocene or early Holocene climatic change might have facilitated local extinctions and/or range shifts among this mammal fauna.Martín Ubilla [martinubilla@gmail.com], Facultad de Ciencias, Universidad de la Republica, Iguá 4225, 11400, Montevideo, Uruguay; Andrés Rinderknecht [apaleorinder@yahoo.com], Museo Nacional de Historia Natural, Paleontología, 11000, Montevideo, Uruguay.