Journal of Arid Environments最新文献

Ungulates have physiological and behavioral mechanisms to respond to seasonal variation and resource availability to meet their nutritional needs. To understand the effects of primary productivity in long-term studies, vegetation indices (e.g., enhanced vegetation index, EVI) can be used as indirect indicators of the nitrogen available to herbivores in arid and mountain environments. In this research, we explore the relationship between the variation in guanaco's local density (Lama guanicoe) and the EVI between 2008 and 2017 in a wild partially migratory population of La Payunia Reserve (Mendoza, Argentina) using a weighted linear regression. Our results indicated a significant relation between guanaco local density and EVI (R² = 0.68; p-value = 0.003), suggesting that the interannual variation in guanaco local density can be explained, at least in part, by higher aerial net primary productivity. Possibly, when nutrient availability is high, the local environment can support a higher local animal density than in years in which primary productivity is lower. When nutrients are limited, some individuals may use other areas not considered in this study. Even preliminary, these results bring new insights into the ecophysiology of this extremely plastic ungulate and contribute to understanding its energetic strategy.

Grasslands restoration is crucial to prevent degradation, with direct seeding being the most effective method. Understanding the species environmental requirements is essential for successful establishment. Our objective was to investigate the effect of water stress and temperature on seed germination of five native forage grass species used in semi-arid Pampas restoration projects. Perennial cool-season grasses (Poa ligularis, Nassella tenuis, Piptochaetium napostaense and Nassella longiglumis) and a warm-season grass (Pappophorum vaginatum) were subjected to different water potentials and temperatures. The hydrotime model was used to describe germination patterns. Results showed a decreasing germination percentage with decreasing water potential, being P. ligularis the most drought sensitive, and P. vaginatum and N. tenuis the least. Warm-season species had the shortest germination time under water stress. Temperature affected germination, with higher values observed at 20, 25 and 15/20 °C. Pappophorum vaginatum was more affected by low temperatures than the cool-season grasses. Poa ligularis, with low water stress tolerance and temperature specificity, may not be recommended for restoration strategies.

Various techniques were used to illuminate domestic structures at EBII Arad (3000-2880 BCE) and its enclaves and outposts in southern Sinai. The dwellings were constructed in a manner that required some form of illumination on overcast days and at night. The residents had three options for lighting the interior of their dwellings: first, sunlight streaming through an open door was the most efficient means of illumination as it did not require the expenditure of fuel; second, the flint “stoves” that were used for cooking provided a certain amount of light; third, lamp-bowls fueled with olive oil were used to illuminate many broadroom dwellings at Arad, but not those in southern Sinai. Lamp-bowls were not used in the latter region because the fuel had to be imported and the amount of light cast by these devices was equivalent to a candle. In this context, hearths were a more appropriate form of illumination as there was a ready supply of firewood in southern Sinai. Lastly, burning olive oil in intact vessels to provide artificial illumination was an act of conspicuous consumption practiced by elites.

Phenological studies with species of cactus have grown in recent decades but the number of species studied remains very low, considering the high species richness of this group. In addition, temporal patterns of flowering and fruiting are important to understanding the processes that govern these crucial events of plant demography and ecology. Based on a five-year study of the reproductive phenology of C. minensis we asked if there is seasonality of flowering and fruiting. Secondly, we tested which climatic variables trigger C. minensis reproductive events in the Espinhaço region. We found that not all individuals produced flowers and fruits each year and a few individuals contributed with most flowers. Flower and immature fruit production is higher during the dry months, with fruits maturing during the rainy season or just before. In general, phenological events were seasonal, except for mature fruit production in 2010 and flower production in 2011. Some phenological traits such as flower timing, frequency, duration, and timing of immature fruit production had not been reported for the genus Cipocereus and were detected only because of the long-term phenological observations. Phenological heterogeneity in cactus might be a response to annual climatic fluctuations, mainly rainfall.

Efficient nitrogen (N) acquisition by plants and microbes and internal reallocation of plant N are crucial for improving ecosystem N retention. However, little is known about shifts in N use strategy between plants and microbes under N addition. We used a¹⁵N tracer to investigate effect of N addition (0–25 g N m⁻² yr⁻¹) on the N use and retention of plant–microbe–soil system in a temperate Chinese steppe. Adding 2–5 g N m⁻² yr⁻¹ increased the ecosystem's ability to retain ¹⁵N (65–76%) after 1 year. Plant N demand during the peak growth period depended strongly on rapid N immobilization by microbes during 7 days (immobilized 45% of ¹⁵N within 24 h). When root biomass exceeded 0.36 kg m⁻², plants competed more strongly for N than the microbes. N addition increased N reallocation from roots to support new shoot growth (79–88% of N), because increased shoot N demand triggered root N transfer when external N was supplied. Thus, the temporal coupling between plant and microbial N use and in N reallocation within plants significantly altered the semi-arid grassland N cycle, and better predicting impacts of future N deposition scenarios.

In the Central Semiarid Region of Argentina, the native woody species Geoffroea decorticans has increased in range and density, probably due to overgrazing. The aim of this work was to evaluate the floristic and functional composition of the herbaceous vegetation along time in grazed sites, within thickets of G. decorticans, and compared to grasslands. We registered the cover of each herbaceous species in different locations within thickets and in the natural grassland, at each season for two years, from autumn 2021 to summer 2023. Indicator species of grasslands were found to be mostly palatable native perennials, resulting more homogeneous than those of thickets. Moreover, the mean cover of palatable species was higher in grasslands than in thickets. Consequently, grasslands confer stability and food resource for livestock. Woody thickets would exhibit a decreased stratification from the center to the edge, that would give rise to niche opportunities and biodiversity reservoirs. Temporal variability in floristic composition indicated differences between grasslands and thickets over time, which decreased in spring, probably by homogenization by grazing in winter. The temporal variability of functional composition showed a cyclical variability in all locations that decreased in spring in all cases.

Seasonally dry tropical forests and woodlands (SDTFW) represent one of the world's most endangered biomes. Approximately 56.3% of its species are non-woody, but little is known about their functional adaptations. The reproductive phenologies of 75 SDTFW species (supplementary material A 1) were studied according to their life forms and seed dispersal syndromes in northeastern Brazil. We used circular statistics and the GLM to assess their seasonalities and relationships of their phenologies with environmental variables. The community exhibited continuous pattern of flowering and fruiting. Flowering and fruiting by most species occurred during only a short period of time and were found to be related to rainfall and photoperiod. Moderate peaks in the seasonal activities of therophytes, hemicryptophytes, and camephytes were observed during the rainy season; succulents and epiphytes flowered all year around but fruited only seasonally. Dispersal modes exhibited seasonality of fruiting in the rainy season, with autochory being predominant over zoochory and anemochory. The observed overlapping of fruiting and flowering periods ensures a consistent resource supply throughout the year and contributes to the preservation of vital ecosystem services. These data highlight the importance of conserving these unique semiarid environments and also provide insights for conservation efforts aimed at preserving SDTFW and safeguarding their biodiversity.

Drought has the most significant impact on arid grassland ecosystems. Managed grazing, including the timing and intensity of defoliation, may interact with drought to differentially affect processes related to soil organic matter decomposition. Extracellular enzyme activity (EEA) provides integrated measure of soil microbial activity which affects nutrient cycling. This study examined EEAs in response to five defoliation regimes and drought at seven grasslands across temperate grasslands of Canada. All sites were dominated by perennial grasses and forbs, but differed in plant species, climate, and soils. Soil samples were analyzed for five EEAs involved in carbon (C), nitrogen (N) and phosphorus (P) cycling. Drought reduced activity of enzymes involved in C cycling, β-glucosidase and β-cellobiosidase by 16 and 17%, respectively, P cycling (acid phosphatase) by 11%, and N cycling (N-acetyl-β-glucosaminidase) by 12%. β-xylosidase showed close association with, and was not affected by drought, suggesting a reduction in C turnover under future drought. β-glucosidase activity was reduced by intermediate defoliation relative to both control and heavy. Acid phosphatase and N-acetyl-β-glucosaminidase were affected by three-way interaction of drought, defoliation and mean growing season precipitation, highlighting the complex mechanism underlying EEA responses. Findings suggest that EEA was affected by drought, but defoliation effects were largely dependent upon drought and local climate.

Aedes aegypti is the primary vector of dengue worldwide and is able to transmit several other arboviruses of public health importance. Despite extensive research on its ecology throughout the world, limited attention has been given to arid regions. The province of San Juan is an arid region of Argentina with unique climatic characteristics commonly known as the “monte ecoregion”. It has scarce precipitation and, therefore, has a network of irrigation canals that supply water to the region. The canal system is outdated, poorly maintained and, accumulating small bodies of water of anthropic origin. Urban ditches were checked from January to December 2019, and during January to June, 771 immature specimens of A. aegypti were found. In this work, we report the presence of A. aegypti in ditches, describing for the first-time new breeding sites that, despite their extreme physical and chemical properties, were used as successful larval habitats. The remarkable adaptability of A. aegypti in this breeding sites raises concerns about the possible detection and spread of dengue cases in the province. The alarming expansion of dengue cases in the region further highlights the urgent need to take control measures against this insect.

Green water is primarily associated with the appearance of annual plants and plays a significant role in biomass production in both arid and semi-arid ecosystems. Herein, we aim to estimate the optimal threshold for determining the presence or absence of annual plants and use them as an ecological indicator to assess potential green water areas in Kuwait as a case study. We integrate remote sensing techniques and MaxEnt modeling. The AUC for the annual plant distribution with all examined factors is 0.847, and the standard deviation is 0.050. The results demonstrated that potential locations with high levels of green water cover <20% of the country. The annual plant distribution was significantly correlated with several types of perennial plants, maximum temperature, precipitation, and sandy soils. It was also found that annual plants are controlled by the spring and winter temperature decline and the timing of precipitation occurrence, especially the pattern and amount of rainfall received in November. Sandy loam and loam soils were found to be ideal for annual plants, although land depressions and soil types are crucial factors in determining annual plant distribution. Additionally, annual plants enhanced the growth of several perennial communities. To reiterate, our study's model helped to comprehend the significance of annual plants as an ecological indicator in sustaining soil moisture over a prolonged period, as well as factors controlling the distribution of annual plants. The developed model and indicators could support decision-makers in determining appropriate locations with adequate levels of green water for revegetation planning in arid landscapes.