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71.
Cristian Echeverría Adrian NewtonLaura Nahuelhual David CoomesJosé María Rey-Benayas 《Applied geography (Sevenoaks, England)》2012,32(2):822-831
A comprehensive understanding of the patterns that occur as human processes transform landscapes is necessary for sustainable development. We provide new evidence on how landscapes change by analysing the spatial patterns of human processes in three forest landscapes in southern Chile at different states of alteration (40%-90% of old-growth forest loss). Three phases of landscape alteration are distinguished. In Phase I (40%-65% of old-growth forest loss), deforestation rates are < 1% yr−1, forests are increasingly degraded, and clearance for pastureland is concentrated on deeper soils. In Phase II (65%-80%), deforestation reaches its maximum rate of 1-1.5% yr−1, with clearance for pastureland being the main human process, creating a landscape dominated by disturbed forest and shrubland. In this phase, clearance for pastureland is the primary driver of change, with pastures expanding onto poorer soils in more spatially aggregated patterns. In Phase III (80%-90%), deforestation rates are again relatively low (<1% yr−1) and forest regrowth is observed on marginal lands. During this phase, clearance is the dominant process and pastureland is the main land cover. As a forest landscape is transformed, the extent and intensity of human processes vary according to the existing state of landscape alteration, resulting in distinctive landscape patterns in each phase. A relationship between spatial patterns of land cover and human-related processes has been identified along the gradient of landscape alteration. This integrative framework can potentially provide insights into the patterns and processes of dynamic landscapes in other areas subjected to intensifying human use. 相似文献
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Adaptive variability to low‐pH river discharges in Acartia tonsa and stress responses to high PCO2 conditions
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Victor M. Aguilera Cristian A. Vargas Marco A. Lardies María J. Poupin 《Marine Ecology》2016,37(1):215-226
Environmental transitions leading to spatial physical–chemical gradients are of ecological and evolutionary interest because they are able to induce variations in phenotypic plasticity. Thus, the adaptive variability to low‐pH river discharges may drive divergent stress responses [ingestion rates (IR) and expression of stress‐related genes such as Heat shock protein 70 (Hsp70) and Ferritin] in the neritic copepod Acartia tonsa facing changes in the marine chemistry associated to ocean acidification (OA). These responses were tested in copepod populations inhabiting two environments with contrasting carbonate system parameters (an estuarine versus coastal area) in the Southern Pacific Ocean, and assessing an in situ and 96‐h experimental incubation under conditions of high pressure of CO2 (PCO2 1200 ppm). Adaptive variability was a determining factor in driving variability of copepods' responses. Thus, the food‐rich but colder and corrosive estuary induced a traits trade‐off expressed as depressed IR under in situ conditions. However, this experience allowed these copepods to tolerate further exposure to high PCO2 levels better, as their IRs were on average 43% higher than those of the coastal individuals. Indeed, expression of both the Hsp70 and Ferritin genes in coastal copepods was significantly higher after acclimation to high PCO2 conditions. Along with other recent evidence, our findings confirm that adaptation to local fluctuations in seawater pH seems to play a significant role in the response of planktonic populations to OA‐associated conditions. Facing the environmental threat represented by the inter‐play between multiple drivers of climate change, this biological feature should be examined in detail as a potential tool for risk mitigation policies in coastal management arrangements. 相似文献
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Juan C. Reyes Francisco A. Galvis Luis E. Yamin Cristian Gonzalez Juan D. Sandoval Pablo Heresi 《地震工程与结构动力学》2019,48(8):888-909
Historic adobe structures pose a high seismic risk mainly because of the poor out-of-plane bending response of their walls that may produce fatalities and significant economic, cultural, and heritage losses. In this paper, we propose a retrofitting technique that increases the wall strength for both in-plane and out-of-plane directions. This technique consists of vertical and horizontal timber elements symmetrically installed on each face of the wall to form a confining wood frame, supplemented with vertical tensors that pre-compress the wall. This study evaluates the performance of this retrofitting technique with a two-set experimental program on full-scale historic adobe walls. On the first set, four specimens were subjected to a static overturning test with boundary conditions representing the confinement effect at both ends by orthogonal walls. On the second set, three full-scale specimens, one unretrofitted and two retrofitted, were subjected to four ground motion records on a shaking table to assess the out-of-plane dynamic behavior of typical corner walls. The unretrofitted specimen collapsed during the second motion (peak ground acceleration [PGA] = 0.39 g), while both retrofitted walls survived all four motions (maximum PGA of 0.75 g) proving the high effectiveness of the proposed retrofitting. The addition of base anchors as a variation of the retrofitting technique significantly reduced the rocking effects and the residual drifts of the system, thus improving its overall seismic performance. Further research is needed to develop guidelines for seismic retrofit of heritage buildings including multistory full-scale tests of specimens with various types of openings and retrofitting strategies that minimize their architectural impact. 相似文献
77.
Northwest Africa 6232: Visible–near infrared reflectance spectra variability of an olivine diogenite
Cristian Carli Giovanni Pratesi Vanni Moggi-Cecchi Francesca Zambon Fabrizio Capaccioni Simone Santoro 《Meteoritics & planetary science》2018,53(10):2228-2242
Visible and near-infrared (VNIR) reflectance is an important spectroscopic technique to identify minerals, and their associations, on planetary body surfaces. Howardites, eucrites, and diogenites (HED) are a class of igneous-like meteorites whose genetic connection with asteroid 4 Vesta has since long been inferred and recently confirmed by Dawn mission results. Pyroxene and olivine are the two major mafic minerals present in HED which can be identified with VNIR reflectance measurements. Thus, studying the compositional variability of those phases and their mixtures by means of laboratory spectroscopic measurements on different diogenitic or eucritic samples is one of the prime methods to better understand the evolution of 4 Vesta's crust. Here, we report the VNIR reflectance spectral analysis of a harzburgitic olivine diogenite, Northwest Africa 6232 (probably paired with Northwest Africa 5480), containing variable amounts of olivine as small grains or aggregates. We found that the olivine diogenite spectral parameters (e.g., band position) of powdered samples and polished slabs are in agreement. Moreover, the olivine diogenite band position shifts from synthetic orthopyroxene in accordance with the presence of olivine and chromite. In particular, the presence of a large olivine clast permits us to determine a linear variation of the band position from synthetic orthopyroxene and olivine, but underestimates the presence of olivine in the olivine diogenite spot. 相似文献
78.
Remus?Pr?v?lieEmail author Georgeta?Bandoc Cristian?Patriche Maria?Tomescu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(8):1923-1939
Climate change analysis is essential, considering the numerous economic and ecological implications of this critical global environmental issue. This paper analyzes the spatial and temporal trends of mean air temperature in Romania’s most important agricultural area, the south and south-eastern region, between 1961 and 2009. In this respect, multiannual (the entire period) and multidecadal (1961–1990, 1971–2000, 1981–2009) trends were analyzed using the Mann–Kendall test and Sen’s slope method at 23 weather stations, annually, seasonally and for the growing season of the region’s main agricultural crops (maize and wheat). Multiannually, the results showed statistically significant temperature increases, on all temporal scales (maximum rate of 0.06 °C/year recorded in summer, equivalent to a net temperature rise of 2.82 °C), except for the autumn season (cooling without statistical significance). Multidecadally, the 1961–1990 period is marked by a general cooling, especially in autumn (maximum values of ?0.07 °C/year or over 2 °C net cooling). In the 1971–2000 and 1981–2009 periods, a general warming was observed (maximum in summer for both multidecades, when positive rates peaked at 0.09 °C/year, or 2.5–3 °C net warming), but the warming of the last three decades is the most prominent in terms of spatial average magnitude and trend significance. Upon analysis of the impact of climate warming on agricultural yields (maize) through linear regression, in the 1991–2000 decade, considered as case study, it was found that in 32 % of the total analyzed area there are evident relationships between the two variables (p value <0.05). In this case, a dependency of 33–50 % (40 %, on average) of maize to climate was found, and a sensitivity (loss) ranging between 0.9 and 1.5 t/ha/year (1.2 t/ha/year, on average) for a 1 °C temperature rise. At the same time, significant losses (of up to 1.7 t/ha/year) of maize for a 1 °C temperature rise were identified in 51 % of the area, but with little p value significance (between 0.05 and 0.1). It is however necessary to analyse the agro-climatic results cautiously, considering that only one decade of climate-agriculture relationship was studied. The results can be useful first and foremost for mitigating the climate change impact on agricultural systems, by prioritizing future adaptation strategies enforced by policy makers. 相似文献
79.
Radu Vacareanu Florin Pavel Ionut Craciun Veronica Coliba Cristian Arion Alexandru Aldea Cristian Neagu 《Journal of Seismology》2018,22(2):407-417
Romania has one of the highest seismic hazard levels in Europe. The seismic hazard is due to a combination of local crustal seismic sources, situated mainly in the western part of the country and the Vrancea intermediate-depth seismic source, which can be found at the bend of the Carpathian Mountains. Recent seismic hazard studies have shown that there are consistent differences between the slopes of the seismic hazard curves for sites situated in the fore-arc and back-arc of the Carpathian Mountains. Consequently, in this study we extend this finding to the evaluation of the probability of collapse of buildings and finally to the development of uniform risk-targeted maps. The main advantage of uniform risk approach is that the target probability of collapse will be uniform throughout the country. Finally, the results obtained are discussed in the light of a recent study with the same focus performed at European level using the hazard data from SHARE project. The analyses performed in this study have pointed out to a dominant influence of the quantile of peak ground acceleration used for anchoring the fragility function. This parameter basically alters the shape of the risk-targeted maps shifting the areas which have higher collapse probabilities from eastern Romania to western Romania, as its exceedance probability increases. Consequently, a uniform procedure for deriving risk-targeted maps appears as more than necessary. 相似文献
80.
Manon Fourrire Hctor Reyes‐Bonilla Cristian Moiss Galvn‐Villa Arturo Ayala Bocos Fabin Alejandro Rodríguez‐Zaragoza 《Marine Ecology》2019,40(3)
Revillagigedo Archipelago and Clipperton atoll are oceanic islands located in the eastern tropical Pacific. The composition and trophic structure of their fish assemblages have never been characterized in detail, and the aim of this study was therefore to analyse the community structure and assess the similarity of fish assemblages between these two areas. Underwater visual fish censuses were conducted using band transects at two depth levels in three islands of the Revillagigedo Archipelago (Socorro, San Benedicto, and Roca Partida) and at Clipperton atoll. We calculated ecological indices (density, richness, Shannon diversity, Pielou evenness, and taxonomic distinctiveness) for each transect. These were compared in order to determine quantitative differences among the islands and bathymetric levels. Qualitative analyses (ANOSIM, nMDS, and SIMPER) were also performed. Finally, we analysed the trophic structure of the assemblages and the functional diversity of the four studied sites. The results showed significant differences for all indices, except diversity (H′). Roca Partida was the site with greatest abundance and richness due to the presence of pelagic species in large numbers. No significant differences were found in functional diversity, suggesting a high degree of ecological redundancy. Lower‐level carnivores with mean trophic level values of between 3.3 and 3.8 dominated both areas. The ordination analysis did not show a clear difference in fish composition among the islands, although Clipperton atoll has a particular fauna characterized by endemic species (Thalassoma robertsoni and Stegastes baldwini). In conclusion, the fish communities of the studied areas seem quite similar, but their assemblage structure differs. In particular, Clipperton is differentiated by the influence of endemic species. 相似文献