El presente estudio tiene como objetivo determinar el efecto de diferentes coberturas arbóreas sobre productividad y calidad de la pradera y sobre variables microclimáticas, en un sistema ...silvopastoril con espino (Acacia caven). Para ello se estableció un ensayo con cuatro tratamientos de cobertura arbórea (0%, 30% - 40%, 50% - 60%, > 70%), en un diseño experimental de bloques aleatorizados completos y tres repeticiones. Además de variables relacionadas con la productividad y calidad de la pradera, mediante sensores se realizó la medición permanente de temperatura y humedad de suelo, temperatura ambiente y humedad relativa. El periodo de análisis incluye dos temporadas de crecimiento de la pradera. Para los análisis estadísticos se consideraron tres modelos; i) la cobertura arbórea sobre la productividad de la pradera; ii) la cobertura arbórea sobre las variables microclimáticas y iii) la cobertura arbórea sobre la productividad pratense, considerando las variables microclimáticas como covariables. Los resultados indican que, en la segunda temporada, la mayor productividad se alcanzó con el tratamiento sin presencia de árboles (0%). No se detectó efecto de la cobertura arbórea sobre la calidad de la pradera, ni sobre variables microclimáticas, para los periodos evaluados. Las variables microclimáticas que mejor explicaron el desarrollo de la pradera fueron la humedad relativa mínima y la temperatura ambiente. Transcurridas dos temporadas de crecimiento, no es factible dilucidar aún cuál tratamiento genera las mejores condiciones para la productividad de la pradera, por lo que se hace necesario continuar con las mediciones.
Vachellia caven has a disjunct distribution at the southern cone of South America, occupying two major ranges: west of Andes (Central Chile) and east of them (mainly the South American Gran Chaco). ...For decades, the species has been subject to various ecological and natural history studies across its distribution, but questions concerning its origin in the western range remain unresolved. Thus far, it is unclear whether Vachellia caven was always a natural component of the Chilean forests, and "how" and "when" the species arrived in the country. In this study, we revised the dispersal syndromes of the species and contrast the two main hypotheses of dispersion to the west of Andes that have been proposed in the 90's, namely animal versus human-mediated dispersal. For this, we reviewed all scientific literature on the species and explored the available information on morphology, genetics, fossil records and distribution patterns of closely related species. Here we illustrate how the collected evidence provides support for the human-mediated dispersal hypothesis, by including a conceptual synthesis that summarizes the outcomes of different dispersal scenarios. Lastly, and regarding the positive ecological effects this species has in the introduced area, we suggest reconsidering the (underappreciated) historical impacts of archaeophytes and rethinking the role that indigenous human tribes may have had in the dispersion of different plants in South America.
•Abandonment of agricultural land triggers vegetation succession to secondary forests.•Slight increase in connectivity during the past 36 years.•Patches of espinal were crucial to promote ...connectivity by acting as stepping stones.
Land use and cover changes have been identified as a major factor contributing to shape landscape structure and biodiversity patterns, particulary in areas with a long history of human occupation and habitat fragmentation, such as the Mediterranean landscapes. However, the existing studies on landscape change indicators for Mediterranean areas have mostly focused in Europe, while for other Mediterranean zones, and especially for South America, there is a serious lack of knowledge concerning the impact of landscape dynamics on ecological processes. Further research on this topic is urgently needed, given the high biodiversity levels and the rapidly increasing rates of human modification in the Mediterranean landscapes of South America. For this purpose, we investigated the dynamics of a landscape in the semiarid region of the Mediterranean zone of Chile, and measured the effect of those dynamics on functional connectivity, during a period of about four decades (1975–2011). Landscape connectivity indicators were extracted from a series of Landsat images. The Equivalent Connnected Area index (ECA) was used as indicator of connectivity trends, and was evaluated for three representative distances of seed dispersal in the study area (150m, 500m and 1000m). In addition, the patches that most contribute to maintain the present connectivity, and their roles as connectivity providers, were identified through a set of commensurable indicators: betweenness centrality and the fractions (intra, flux connector) of the Integral Index of Connectivity. We found that these indicators were useful to detect and summarize a number of previously unreported trends in these Mediterranean landscapes. First, population growth and economic development were compatible with an increase in functional connectivity for forest habitats, mainly because the abandonment of marginal agricultural lands and their subsequent conversion to espinals (Acacia caven) triggered vegetation succession towards secondary forests. Second, increased forest connectivity was not associated to a decrease in the characteristic heterogeneity of Mediterranean landscapes. Third, many patches of espinal, despite being commonly regarded as of poor conservation value, were crucial to promote connectivity by acting as stepping stones among other patches with higher habitat quality. The approach here presented provides a combined assessment of landscape structure, function and change that should be valuable and applicable to deliver operational indicators in dynamic landscapes in South America and other Mediterranean regions.
Unlike the theatre and literature, the cinema does not seem to have sufficiently addressed gender discrimination in Medicine. From this perspective, the present work addresses the eventful life of ...Henriette Faver Caven, who had to study, practise and impart her medical acumen dressed as a man, and rescues its current repercussions in cinematography. Henriette Faver Caven is sketched from her birth to her death through an analysis of the different phases of her life (orphaned at an early age, the death of her uncle, husband and daughter, cross-dressing, graduation, her involvement in the war, prison, emigration to Cuba -the first female doctor on the island- her professional activities, homosexual marriage, trial, conviction and exile). At the same time, we allude to two Cuban films about her life by Lídice Pérez López Enriqueta Faver (1998) and Favez (2004), with their different presentations at cinematographic festivals. We estimate that this issue and corresponding cinematographic initiatives are of great value for debating not only the harsh story of the access of this woman to formal studies in general, and university level education in particular, but also the problems of gender, and to relate this singular existence to both its cinematographic recreations and its literary and theatrical repercussions.
Canopy conductance (gc ) is the main controller of plant-atmospheric interaction and a key element in understanding how plants cope with drought. Empirical gc models provide a good inference as to ...how environmental forcing affects surface water vapor and CO2 gas exchange. However, when facing water scarcity, soil moisture or plant water availability becomes the primary controller. We studied gc in an Acacia caven (Mol) savannah in Central Chile under Mediterranean-type climate conditions that present distinguishable wet and dry seasons. We calibrated an empirical gc , in order to account for whole canopy gas exchange with gc measurements from three different data sets: (1) an inversion of the Penman-Monteith equation in combination with a Shuttleworth and Wallace model (PMSW) for evapotranspiration from sparse canopies; (2) an inversion of the Penman-Monteith (PM) based on the big leaf approach and (3) a set of leaf stomatal conductance (gs ) ground based measurements taken throughout the season and scaled up to the canopy level. Then the semi-empirical Farquhar-Ball-Berry (FBB) gc model was added to the comparison to evaluate if the inclusion of a mechanistic component for photosynthesis would improve the prediction of gc . Models performance was assessed with ground based leaf gas exchange measurements during both wet and dry seasons. Acacia's gc showed a high synchronicity with soil moisture, exhibiting the typical isohydric behavior of this kind of vegetation. The addition of the Shuttleworth and Wallace modifier to the Penman-Monteith equation did not yield a better calibration for the multiplicative model when compared to the one calibrated with the PM gc data set, however this does not directly certifies that PM itself is a better estimator of gc in sparse canopies. Furthermore, scaling issues such as ecosystem heterogeneity and patchiness must be considered when applying these estimations to a watershed level for both eco and hydrological reasons. These empirical models demonstrated to be a good tool for predicting stomatal behavior for this kind of vegetation. Nevertheless, the effect of deep soil moisture on plant water status must be integrated in gc estimations in order to improve model's performance.
Changes in soil biota following fire and its successive influence on their interactions with plants may have direct implications on the invasion success of woody alien species in fire-prone ...ecosystems. In this work, we experimentally addressed if soil biota from burned and unburned areas differentially affect growth and nutrition of two dominant woody natives (Lithraea molleoides and Vachellia caven) and three woody invaders (Gleditsia triacanthos, Ligustrum lucidum and Pyracantha angustifolia) that occur on fire-prone ecosystems of central Argentina. Our results indicate that growth and P content in tissues of both woody natives Lithraea and Vachellia were generally benefited by arbuscular mycorrhizal fungi (AMF) and that these effects did not strongly differ between AMF communities from burned and unburned soils. In the case of alien species, differences in growth and nutrition in response to AMF were related more to the identity of the invader than on the provenance of the soil biota. This study provides evidence on the important role that soil biota may have in the success of woody aliens in these ecosystems and on the functional stability of AMF communities facing disturbances.
Seasonal precipitation is critical for springtime plant activity, and a direct connection may exist between the rainfall frequency and intensity with vegetation productivity in dryland ecosystems. ...This connection has been poorly quantified in the semi-arid Mediterranean region of Chile. In this work, we describe the effects of the monthly frequency (λ) and intensity (α) of rainfall events on two satellite-derived Enhanced Vegetation Index (EVI) descriptors: the time-integrated vegetation index (mEVI), a surrogate for total potential productivity, and the maximum vegetation index (iEVI), a surrogate for maximum photosynthetic activity, in a shrubland ecosystem dominated by Acacia caven. Time series analyses over a period of 15 years (2000–2014) were carried out for assessing their relationships and lags. Rainfall descriptors largely explained the temporal variation in vegetation productivity. Values of mEVI and iEVI showed a short-term statistical dependence of up to 4 months with precipitation frequency, meaning that vegetation productivity was delayed compared to the occurrence of rain events. This delay might be related to soils acting as water reservoirs being used by different plant types at different times and soil depths, i.e., herbs using water from the upper soil horizons with small lags in relation to rain pulses, while shrubs drawing water from deeper in the soil would exhibit greater range of lags. The asynchrony between rainfall events and suitable environmental conditions for growth, and the ability of plants to draw water at different soil depths with different lags may be an ecological adaptation to the high inter- and intra-annual rainfall variability.
Hydraulic fracture operation is one of the key technologies for the development of caven reservoirs. Modeling of hydraulic fracture processes to factors such as Situation of tensions, Shear strength ...and Orientation of natural fractures in the reaction(In particular, the potential for opening cracks in areas that are growing along the path of a hydraulic fracture) And also the length and height of the hydraulic fracture. Due to the presence of natural fractures with diffuse penetration and different orientations, the operation is complicated in caven reservoirs. For this purpose, two numerical methods are proposed for simulating the hydraulic fracture in caven reservoirs.In this paper, the hydraulic fracture model is considered in terms of the state of tensions, On the reaction between the hydraulic fracture and the natural fracture (45 °) And also the effect of length and height of hydraulic fracture, Developed and how to distribute induced stress around the well, In order to determine the direction in which the hydraulic fracture is formed in that direction The finite difference method and theindividual element for numerical solution are used and simulated.An inverse suction is an important parameter And in the operation of the hydraulic fracture will reduce production,This simulation is being studied. In every length of the hydraulic fracture, The rate of production is measured and the causes of changes in the input rate to the wells are discussed based on the natural fractures cut by the hydraulic fracture and the induction of the fracture. Finally, it can be seen that the optimum hydraulic fracture time will be The hydraulic fracture is able to connect natural fractures with large and large streams And finally, it is connected to the well, and there is a fundamental difference between the tensile and shear opening. The analyzes indicate that the growing hydraulic fracture, the tensile and shear stresses applied to the natural fracture.
The successional pathways linking the Acacia caven‐dominated savanna habitat “espinal” and the closed sclerophyllous forest of central Chile have long been debated. Previously, espinal was considered ...an invasive degradation of closed forest that tended toward desertification, could not be restored to forest, and had little ecological value. Recent GIS (Geographical Information System) research on land‐use change has, however, detected apparent regeneration of sclerophyllous forest from espinal. This suggests that there is a successional path linking espinal and sclerophyllous forest. Here, we used surveys of transects in espinals and espinal–sclerophyllous forest transitions to ask whether (1) A. caven is an invasive species or a pioneer species, (2) forest regenerates by sclerophyllous trees “filling in” spaces between A. caven individuals, and then shading them out (plant–plant competition), or (3) forest regenerates by plant–plant facilitation between A. caven and other species, and (4) how current and historical management and condition affect these potential successional mechanisms. We find that A. caven establishes primarily in full sunlight and is unlikely to degrade forests via invasion. We also find, for the first time, evidence that A. caven is a nurse tree to several sclerophyllous forest tree‐beneficiary species. Measurements of the under‐canopy microhabitat of A. caven, compared to Lithraea caustica, another possible nurse species, suggest that it provides a balance between shade and soil moisture retention, making it a regeneration site not only for directed bird‐dispersed seeds but also for undirected wind‐dispersed ones. Conservation and restoration of espinals, especially in drier areas, could provide capacity for future dynamic successional pathways in central Chile.
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