Subtropical Semiarid Research Articles

Glacial to periglacial transition at the end of the last ice age in the subtropical semiarid Andes

Atmospheric warming and circulation reorganization at the end of the last ice age represent the most important climate change of the last 100,000 years and provide an opportunity to uncover how the southern subtropics cryosphere responded to strong changes in the global climate system. Extensive mapping and chronologic records on cryogenic landforms to better understand the association and interactions between glaciers and viscous creep of ice-rich permafrost landforms (rock glaciers) are widely missing in the region. In this paper, we reconstruct the geomorphic imprint of the Last Glacial Maximum (LGM) and the Termination I in the high Andes of the Río Limarí Basin (30–31°S) in the subtropical semiarid Andes of Chile. 74 new 10Be surface exposure dating ages constrain the timing of glaciation, deglaciation, and glacial to periglacial transition. Glacial advances occurred first by 41.2 ± 0.6 – 35.0 ± 0.5 ka during Marine Isotope Stage 3, but probably earlier also; then, a second advance occurred during the global LGM between 24.2 ± 0.4 and 18.6 ± 0.2 ka. Deglaciation by 17.6 ± 0.2 ka left extensive hummocky moraines on the main valleys. Characteristic patterns of furrows and ridges typical of rock glaciers and solifluction superimposed on the LGM hummocky moraine indicate ice-rich permafrost in glacial deposits likely between 15.5 ± 0.3 and 13.6 ± 0.3 ka. We propose that moraines deposited by LGM debris-covered glaciers served as a niche for strong seasonal frost and permafrost creep, which substantially modified the original landforms. Our results contribute to a better understanding of major transformations in an ice-rich high mountain area of the southern hemisphere where the interplay of temperature and precipitation changes drove glacial to periglacial transitions.

Late Quaternary glacier advances in the Andes of Santiago, central Chile, and paleoclimatic implications

Andean mountain glaciers in central Chile are in a transitional zone between the seasonal influence of the mid-latitude westerlies and subtropical semiarid conditions to the north. Long-term glacial dynamics for these glaciers and their relationship with the paleoclimate during the late Quaternary are poorly known despite their relevancy. We estimate here the timing and extent of late Pleistocene–early Holocene glaciers in the Andes of Santiago (33°50′S) from geomorphological and geochronological analyses. Our observations evidence that a glacial stage occurred before the Last Glacial Maximum (ELGM) at the San Gabriel drift (1,300 m a.s.l.), dated as ∼46–36 ka. Glacial stages during the latest Pleistocene–early Holocene transition period, partially concomitant with the Antarctic Cold Reversal (ACR) and with the Younger Dryas (YD) chronozones, were identified and dated at La Engorda drift (2,450–2,570 m a.s.l.) at ∼15–10 ka. We propose that the San Gabriel drift represents a prolonged glacial advance driven by increased precipitation and cold conditions off central Chile during glacial times. In La Engorda drift, late glacial advances occurred associated with increased regional precipitation, in the context of a transition from humid to arid climate in central Chile, concomitantly with a general warming trend of sea surface temperatures offshore in the southeastern Pacific and with reduced austral summer insolation. The results support the sensitivity of the Andean mountain glaciers to precipitation and paleoclimate conditions, most possibly associated with periods of increased northward influence of the mid-latitude westerlies during glacial and late glacial times, in addition to the El Niño/Southern Oscillation (ENSO) impact since the mid-Holocene, driving late Quaternary glacier advances in central Chile. We estimate a maximum variation of ∼1,200 m in the position of the late Quaternary Equilibrium Line Altitude (ELA), inferred at ∼3,400 m and ∼3,600 m a.s.l. at the time of the San Gabriel and La Engorda drifts, respectively, with respect to its modern location close to 4,600 m a.s.l.

Morphogenetic Diagnostics and Nomenclature of Alluvial-Meadow Soils in the Subtropical Semiarid Area, Floodplain of the Kur River, Azerbaijan

The aim of this study was to evaluate morphologic features, diagnostic qualifiers and enhance classification of alluvial-meadow soils in the floodplain of the Kur River within Azerbaijan. For this purpose, several soil pits were placed in the representative test areas and multiple soil samples collected within field campaigns (2014–2015). Based on the field and laboratory test data, the detailed soil maps of the test areas were compiled, and diversity of alluvial-meadow soils was classified as suborders (subtypes): alluvial-meadow primitive; alluvial-meadow layered (flaggy); alluvial-meadow dark and alluvial-meadow irrigated. It was found out that in the floodplains, local soil variability was predominantly attributed to not only alluvial sediments, but also water table, mineralization rate and salt content of underground water as well flood water play an important role. The mineralization of ground water is weak (1.40–3.70 g/l) and the concentration of hydro-carbonates (HCO3−) varies from 0.56 to 0.92 g/l. No salinization indication found in the profile of alluvial-meadow primitive and alluvial-meadow layered soils, while weak concentration (solid content = 0.40–0.54%) was found at a depth of 80–150 cm in the alluvial-meadow dark soil. Unlike other subtypes, alluvial-meadow dark soil is characterized with the higher biomass (green weight of top = 41.5 cwt/ha and green weight of underground = 142.3 cwt/ha), high mobility of humus substances with predominance of the 1st fraction of humin (20.0–28.1%) and fulvic acids (14.6–22.3%). The ratio of Cha : Cfa reaches 1.18–1.32. For the alluvial-meadow irrigated soil, the second fraction of humin acid (9.3–10.2%) and total content of humin acid ranges from 45.6 to 50.3%. The ratio of Cha : Cfa is larger (1.37–1.50). Depending on the lithology of alluvial sediments, the content of SiO2and R2O3 varies in the ranges of 53.0–57.2% and 9,6–26,0%, respectively. For the alluvial-meadow dark soil, decomposition of alum silicates in alkaline hydrolysis is typical (8.7–9.0). The content of SiO2and R2O3 varies between 47.8 and 50.6 %, and 19.7 and 21.6%, respectively. In the topsoil, of the irrigated soils in associated to washing out the content of Ca and CaO content (12.2–13.1%) increases in deeper horizons.

Ephemeral habitat supports high fish α‐diversity and β‐diversity during drought in a subtropical semiarid wetland

ABSTRACTGlobally, the number of rivers with intermittent flow is increasing due to climate change and water abstraction for human consumption. Currently, our understanding of how hydrology in subtropical rivers with intermittent flow affects the structure and dynamics of aquatic communities is poorly understood. Here, we investigated how fish α‐ and β‐diversity patterns in intermittent channels in the lower reaches of the Okavango Delta respond to seasonal flooding and drought. Under low‐flow conditions, ephemeral habitat had higher α‐diversity, and this was influenced by a combination of fish aggregation and apparent transient legacy effects as habitat patches became smaller and more isolated. Investigation of changes in fish assemblage structure across different hydrological periods and habitat types showed significant species turnover when water levels fell, suggesting a strong influence from species sorting. During high‐water periods, species assemblages were homogenized both at local and regional scales, suggesting a greater influence of mass effects. Our findings support hydrology as a major factor regulating diversity patterns in intermittent rivers of a major wetland in a semiarid region of subtropical Africa. We infer from these findings that maintenance of a relatively natural flow regime will be necessary for conserving aquatic ecosystem structure and function in this system.

Compost and Biochar to Promote Soil Biological Activities under Sweet Potatoes Cultivation in a Subtropical Semiarid Region

South Texas is located in a subtropical semiarid climate, and due to high temperature and irregular precipitation, farmers opt to leave their fields fallow during the summer months jeopardizing overall soil health. We evaluated whether sweet potato (Ipomoea batatas) cultivation coupled with drip irrigation could restore soil biological activities compared with bare fallow. Additionally, because sweet potatoes have high demand of soil nutrients, especially potassium (K), we evaluated the nutrient supply of locally sourced soil amendments. Sweet potato was cultivated during summer 2018 in McAllen, Texas, under control (no fertilizer), NPK (synthetic fertilizer), RC (yard-waste compost), and AC (compost produced under an enhanced composting process), and biochar (gasified walnut shell at 900°C), each with three replicates. Soil amendments were applied at different amounts to result in a rate of 80 kg K ha−1. Soil biological indicators were microbial biomass phosphorous, phosphatase activity, and the rate of fluorescein diacetate hydrolysis (FDA). Available nitrogen, phosphorus, potassium, and sodium were also quantified. Aboveground biomass and storage root yield estimated sweet potato’s agronomic performance. Cultivation and irrigation stimulated soil enzyme activities and microbial biomass-phosphorous. Sweet potato yields were the highest in NPK treatment but still 2.8 times lower than variety’s potential yield. Storage root yield was inversely related to aboveground biomass, suggesting that growing conditions benefited the production of shoot versus roots. Both biochar and AC treatments stimulated FDA rates and K availability. Soil pH and sodium concentration increased in all treatments over the growing season, possibly due to river-sourced irrigation water. Together, these findings show that crop cultivation promoted soil biological activities and the maintenance of nutrient cycling, compared to bare-fallow conditions. For a better agronomic performance of sweet potato, it would be necessary to identify management practices that minimize increase in soil pH and salinity.

Morphogenetic Diagnostics and Nomenclature of Alluvial-Meadow Soils in the Subtropical Semiarid Area, Floodplain of the Kur River, Azerbaijan

Abstract—The aim of this study was to evaluate morphologic features, diagnostic qualifiers and enhance classification of alluvial-meadow soils in the floodplain of the Kur River within Azerbaijan. For this purpose, several soil pits were placed in the representative test areas and multiple soil samples collected within field campaigns (2014–2015). Based on the field and laboratory test data, the detailed soil maps of the test areas were compiled, and diversity of alluvial-meadow soils was classified as suborders (subtypes): alluvial-meadow primitive; alluvial-meadow layered (flaggy); alluvial-meadow dark and alluvial-meadow irrigated. It was found out that in the floodplains, local soil variability was predominantly attributed to not only alluvial sediments, but also water table, mineralization rate and salt content of underground water as well flood water play an important role. The mineralization of ground water is weak (1.40–3.70 g/L) and the concentration of hydro-carbonates (HCO3) varies from 0.56 to 0.92 g/L. No salinization indication found in the profile of alluvial-meadow primitive and alluvial-meadow layered soils, while weak concentration (solid content = 0.40–0.54%) was found at a depth of 80–150 cm in the alluvial-meadow dark soil. Unlike other subtypes, alluvial-meadow dark soil is characterized with the higher biomass (green weight of top = 41.5 c/h and green weight of underground = 142.3 c/h), high mobility of humus substances with predominance of the 1st fraction of humin (20.0–28.1%) and fulvic acids (14.6–22.3%). The ratio of Ch.a : Cf.a reaches 1.18–1.32. For the alluvial-meadow irrigated soil, the second fraction of humin acid (9.3–10.2%) and total content of humin acid ranges from 45.6 to 50.3%. The ratio of Ch.a : Cf.a is larger (1.37–1.50). Depending on the litho logy of alluvial sediments, the content of SiO2 and R2O3 varies in the ranges of 53.0–57.2 and 9.6–26.0%, respectively. For the alluvial-meadow dark soil, decomposition of alum silicates in alkaline hydrolysis is typical (8.7–9.0). The content of SiO2 and R2O3 varies between 47.8 and 50.6%, and 19.7 and 21.6%, respectively. In the topsoil, of the irrigated soils in associated to washing out the content of Ca and CaO content (12.2–13.1%) increases in deeper horizons.

High-resolution paleomagnetic constraint on the oldest hominoid- fossil-bearing sequence in the Xiaolongtan Basin, southeast margin of the Tibetan Plateau and its geologic implications

Abstract Sediments in the Xiaolongtan Basin at the southeastern margin of the Tibetan Plateau (SEMTP) not only contain an abundance of the oldest Chinese hominoid fossils, but also a record of the evolution of the Indian monsoon and the uplift of the southeastern Tibetan Plateau. However, these Middle–Upper Miocene sedimentary sequences have lacked a precise chronology, hampering our ability to reconstruct the regional tectonic uplift and the paleoecological environment. We carried out high-resolution paleomagnetic dating throughout the fluviolacustrine sequence in the Xiaolongtan Basin. The 487.5 m-thick sequence here revealed 11 reversed and 11 normal zones that span from chron 5n.2n to chron 5ACr, yielding magnetostratigraphic ages of ~14.1–10.0 Ma for the section, and 12.5 Ma and 11.7 Ma for the two hominoid-fossil bearing beds. Combined with lithological analyses and the evidence for ecological characteristics, we suggest that four notable ecological environmental phases had emerged in the Xiaolongtan Basin after it was formed at around 14.1 Ma. These were as follows: Phase I (14.1–12.6 Ma) with humid-hot forest steppe, Phase II (12.6–11.6 Ma) with subtropical evergreen broad-leaved forest, Phase III (11.6–10.0 Ma) with a hot-dry and evaporative shallow lake and Phase IV (after 10.0 Ma) with a subtropical semiarid steppe environment. After ~10.0 Ma deposition gradually ceased, albeit recurring sporadically until the Early Pleistocene.

Detecting Eutrophication Symptoms in a Subtropical Semi-Arid Coastal Lagoon by Means of Three Different Methods

Excess supply of nutrients of anthropogenic origin is one of the main drivers of global change that is affecting the ecological function and provision of ecosystem services by coastal wetlands. This study examines the response of a subtropical semi-arid coastal lagoon to anthropogenic nutrient input, through the use and comparison of eutrophication indices and models, and compares the usefulness of such methods to identify eutrophication symptoms. The Lobos Lagoon is located on the eastern coast of the Gulf of California and receives agricultural and urban wastewater discharges. To identify potential eutrophication symptoms, the Trophic IndeX (TRIX), the Arid Zone Coastal Water Quality Index (AZCI) along with the Assessment of Estuarine Trophic Status (ASSETS) model were used. Lobos Lagoon was found to have good environmental condition; however eutrophication symptoms were identified in the zone where untreated urban and agricultural wastewaters are discharged. Results obtained using the three methods were consistent and, thus, their performance can be considered as good and complementary, and can be used to evaluate the extent of eutrophication in subtropical semi-arid coastal lagoons.

Melt and surface sublimation across a glacier in a dry environment: distributed energy-balance modelling of Juncal Norte Glacier, Chile

ABSTRACTPrevious estimates of melt and surface sublimation on glaciers of the subtropical semiarid Andes (29–34°S) have been obtained at few specific locations, but it is not clear how ablation components vary across the entire extent of a glacier in this dry environment. Here, we simulate the distributed energy and mass balance of Juncal Norte Glacier (33°S) during a 2-month summer period. Forcing fields of near-surface air temperature and wind speed are generated using two methods accounting for the main physical processes that shape their spatial variations. Simulated meteorological variables and ablation agree well with observations on the glacier tongue and reveal complex patterns of energy and mass fluxes. Ablation decreases from 70 mm w.e. d−1 at the low-albedo glacier terminus (~3000 m), where almost 100% of total ablation corresponds to melt, to <5 mm w.e. d−1 at wind-exposed, strong-radiated sites above 5500 m, where surface sublimation represents >75% of total ablation. Our simulations provide the first glacier-scale estimates of ablation components on a glacier in the study region and better reproduce the observed and expected spatial variations of melt and surface sublimation, in comparison with more simple assumptions, such as linear gradients and uniform wind speeds.

The effects of seasonality and precipitation in the avifauna of the Argentine Southern Chaco Serrano

In subtropical regions like the Chaco Serrano (33° S), rainfall has a marked seasonality, and water flood, caused by heavy rains, may have important consequences for dependent ecosystems. Conversely, the high pressure on available resources during dry periods can also affect the fauna diversity and distribution. Even though birds have shown to be excellent ecological indicators of these shifts in the environment, currently little is known about the avifauna of the Argentine Chaco Serrano phytogeographic district. Our aim was to study the resident bird population status in the Southern Chaco Serrano, its fluctuations in richness and abundance, and its relationship to seasonal variations, in monthly and annual hydroperiods. In order to assess the resident bird status over a two year period (2011 Mar.-2013 Feb.) we carried out 18 sampling surveys during pre-breeding (spring), breeding (summer) and non breeding periods (autumn-winter), in the Northeastern part of the Valle Fertil Natural Park, San Juan province, Argentina. During each site survey, we recorded bird assemblages found in six transects, and obtained bird abundance and species diversity. A mixed general linear model was employed to evaluate relationships between the studied variables. We found a total of 98 species of birds belonging to 33 families (44 resident species, 23 spring visitors, six summer visitors, two winter visitors and 23 with scarce registers). We also registered 68 of these species in both hydroperiods, 28 only during rainy periods and only two during the dry period. Both richness and abundance showed the highest values during the pre-breeding and rainy seasons, while different tendencies were detected during the isolated monthly rainfalls. These changes in bird densities were associated with the arrival of migratory species, mainly spring visitors, and probably in relationship with their reproductive activity, and to seasonal fluctuations in food resources. The Southern Chaco Serrano is a subtropical semiarid place that seems to be an important breeding habitat for many migrant bird species, which in turn promoted seasonal changes in species density and diversity, mainly during rainy years. This work contributed to our understanding on the causes of richness and abundance variations on birds, and will contribute to this important group management and conservation in this area.

Efecto de la estacionalidad y lluvias en la avifauna del Chaco Serrano Austral, Argentina

In subtropical regions like the Chaco Serrano (33° S), rainfall has a marked seasonality, and water flood, caused by heavy rains, may have important consequences for dependent ecosystems. Conversely, the high pressure on available resources during dry periods can also affect the fauna diversity and distribution. Even though birds have shown to be excellent ecological indicators of these shifts in the environment, currently little is known about the avifauna of the Argentine Chaco Serrano phytogeographic district. Our aim was to study the resident bird population status in the Southern Chaco Serrano, its fluctuations in richness and abundance, and its relationship to seasonal variations, in monthly and annual hydroperiods. In order to assess the resident bird status over a two year period (2011 Mar.-2013 Feb.) we carried out 18 sampling surveys during pre-breeding (spring), breeding (summer) and non breeding periods (autumn-winter), in the Northeastern part of the Valle Fértil Natural Park, San Juan province, Argentina. During each site survey, we recorded bird assemblages found in six transects, and obtained bird abundance and species diversity. A mixed general linear model was employed to evaluate relationships between the studied variables. We found a total of 98 species of birds belonging to 33 families (44 resident species, 23 spring visitors, six summer visitors, two winter visitors and 23 with scarce registers). We also registered 68 of these species in both hydroperiods, 28 only during rainy periods and only two during the dry period. Both richness and abundance showed the highest values during the pre-breeding and rainy seasons, while different tendencies were detected during the isolated monthly rainfalls. These changes in bird densities were associated with the arrival of migratory species, mainly spring visitors, and probably in relationship with their reproductive activity, and to seasonal fluctuations in food resources. The Southern Chaco Serrano is a subtropical semiarid place that seems to be an important breeding habitat for many migrant bird species, which in turn promoted seasonal changes in species density and diversity, mainly during rainy years. This work contributed to our understanding on the causes of richness and abundance variations on birds, and will contribute to this important group management and conservation in this area.

Shrub biomass estimation in the semiarid Chaco forest: a contribution to the quantification of an underrated carbon stock

The quantification of biomass of woody plants is at the basis of calculations of forest biomass and carbon stocks. Although there are well-developed allometric models for trees, they do not apply well to shrubs, and shrub-specific allometric models are scarce. There is therefore a need for a standardized methodology to quantify biomass and carbon stocks in open forests and woodlands. To develop species-specific biomass estimation models for common shrubs, as well as a multispecies shrub model, for the subtropical semiarid Chaco forest of central Argentina. Eight shrub species (Acacia aroma, Acacia gilliesii, Aloysia gratissima, Capparis atamisquea, Celtis ehrenbergiana, Larrea divaricata, Mimozyganthus carinatus, and Moya spinosa) were selected, and, on average, 30 individuals per species were harvested. Their total individual dry biomass was related with morphometric variables using regression analysis. Crown area as well as crown-shaped variables proved to be the variables with the best performance for both species-specific and multispecies shrub models. These allometric variables are thus recommended for standardized shrub biomass assessments. By accounting for the shrub component of the vegetation, our models provide a way to improve the quantification of biomass and carbon in semiarid open forest and woodlands.

Asymmetric Contribution of Isotopically Contrasting Food Sources to Vertebrate Consumers in a Subtropical Semi-arid Ecosystem

Habitat heterogeneity is a primary ecological factor that is particularly pronounced in arid ecosystems. The Tehuacan valley is a subtropical semi-arid ecosystem in which several species of columnar cacti and agave (i.e., CAM plants) constitute the dominant elements accompanied by patches of trees and shrubs (i.e., C3 plants). Vegetation in Tehuacan is isotopically heterogenous because CAM plants have less depleted δ13C values than C3 plants. Fruits and flowers of cactus and agaves offer abundant food to vertebrates, but their leaves might be less attractive to insects than the leaves of C3 plants. Therefore, we use carbon and nitrogen stable isotope analysis to test the hypothesis that C3 and CAM food would contribute asymmetrically to different guilds of birds and bats. We predict that granivorous and frugivorous birds and nectarivorous and frugivorous bats will consume a CAM diet, whereas insectivorous birds and bats will consume a C3 diet. Due to omnivory of bird and bat consumers, we predict that the importance of CAM food will decrease as the trophic level of the animal increases. Our results showed that CAM food predominated in plant-eating birds and in some flower-visiting bats, whereas C3 food predominated in insect-eating bats and birds and frugivorous bats. Habitat heterogeneity in Tehuacan is important for conservation due to the asymmetric role of CAM and C3 food in the nutrition of different feeding guilds of vertebrates. Our study provides basic information to evaluate the potential impact of habitat loss on functional groups of consumers in a semi-arid ecosystem. Resumen La heterogeneidad del habitat es un factor ecologico primario que es particularmente pronunciado en los ecosistemas aridos. El valle de Tehuacan es un ecosistema subtropical semiarido en el que varias especies de cactaceas columnares y agaves (e.g., plantas MAC) constituyen los elementos dominantes acompanados por grupos de arboles y arbustos (e.g., plantas C3). La vegetacion en Tehuacan es isotopicamente heterogenea ya que las plantas MAC tienen valores de δ13C menos negativos que las plantas C3. Las frutas y las flores de cactus y agaves ofrecen comida abundante a los vertebrados, pero sus hojas podrian ser menos atractivas para los insectos que las hojas de las plantas C3. Por lo tanto, utilizamos analisis de isotopos estables de carbono y nitrogeno para probar la hipotesis de que los alimentos C3 y MAC contribuyen asimetricamente a los gremios de aves y murcielagos. Predecimos que las aves granivoras y frugivoras, y los murcielagos frugivoros y nectarivoros consumiran una dieta MAC, mientras que las aves y murcielagos insectivoros consumiran una dieta C3. Debido a la omnivoria de aves y murcielagos, predecimos que la importancia del alimento MAC disminuira a medida que el nivel trofico de los animales aumente. Nuestros resultados mostraron que el alimento MAC predomino en aves herbivoras y en algunos murcielagos nectarivoros, mientras que el alimento C3 predomino en los murcielagos y aves que se alimentan insectos y en los murcielagos frugivoros. La heterogeneidad del habitat en Tehuacan es importante para la conservacion debido al papel asimetrico de los alimentos MAC y C3 en la nutricion de los diferentes gremios alimentarios de vertebrados. Nuestro estudio proporciona informacion basica para evaluar el posible impacto de la perdida de habitat en los grupos funcionales de los consumidores en un ecosistema semiarido.

Variación Estacional de un Ensamble de Aves en un Bosque Subtropical Semiárido del Chaco Argentine

ABSTRACTWe studied seasonal variation in bird assemblages in a Chaco subtropical semiarid forest, Santiago del Estero Province, Argentina. We carried out seven samplings during both breeding and non breeding periods, in order to assess the resident status and the trophic guild of each species. During the last four samplings we recorded bird populations using 30 fixed‐radius points, in order to estimate bird density, species density, evenness, and species diversity. We found that: (1) the bird assemblage had 96 species (67 residents, 19 summer migrants, 1 winter migrant, 5 of doubtful residency and 4 species whose resident status was unknown); (2) higher values of species density, evenness and species diversity were found during breeding periods; and (3) higher community attributes were followed by higher densities of 4 trophic guilds: nectarivores, frugivores and short and long‐flight insectivores during the breeding periods. Changes in guild densities were probably associated with the arrival of summer migrants and to seasonal fluctuations in food resources, which in turn promoted seasonal changes in species density and diversity. Different from observations in other avian assemblages of the Chaco, no temporal variations were observed in the terrestrial seedeaters guild. This could be due to the fact that our study site forests are located in a landscape matrix with agricultural fields and grasslands that may offer year‐round seed supply. The Chaco subtropical semiarid forest seems to be an important breeding habitat for many migrant species from both Neotropical and Nearctic regions.RESUMENEntre 1997 y 1999, se analizaron las variaciones estacionales de los atributos comunitarios (diversidad, densidad de especies y equitatividad) y de la densidad de gremios tróficos en un ensamble de aves del bosque subtropical semiárido del Chaco argentine. Se realizaron siete muestreos que abarcaron tanto los perfodos reproductivos como los no reproductivos, lo que permitió clasificar a las especies segün su estatus de residencia. En los cuatro ültimos de esos siete muestreos se dispusieron 30 puntos de conteo de radio fijo dentro del bosque para hacer las estimaciones de densidad, densidad de especies, equitatividad y diversidad de aves. Los resultados indicaron: (1) que el ensamble estuvo compuesto por 96 especies (67 residentes, 19 migrantes estivales, 1 migrante invernal, 5 de residencia dudosas y 4 accidentales); (2) que los mayores valores de diversidad, densidad de especies y equitatividad se observaron durante perfodos reproductivos; y (3) que los cambios en estos atributos comunitarios estuvieron acompañados por aumentos significativos en las densidades de los gremios de nectarfvoras, insectivoras de vuelo corto, insectivoras de vuelo largo y frugivoras durante los periodos reproductivos. Es probable que los cambios estacionales observados en estos gremios estén asociados al aporte del componente migratorio estival y respondan a los incrementos en los niveles de recursos (néctar, frutos e insectos voladores) que tienen lugar en estos ambientes durante la estación hümeda. Estos cambios gremiales son los que en definitiva promueven los aumentos de los atributos comunitarios. A diferencia de lo observado para otros ensambles de aves en el Chaco, no detectamos variaciones temporales en el gremio de las semilleras terrestres. Esto podria deberse a que en el área de estudio los bosques están insertos en una matriz de paisaje que cuenta con áreas agricolas y de pastizales que probablemente provean ofertas sostenidas de semillas a lo largo de todo el año. Es importante destacar la importancia de los bosques subtropicales semiáridos Chaquenos como hábitat de reproducción para las especies migrantes neotropicales y neárticas.

Vegetative, reproductive, and physiological Adaptations to aridity of pitayo (Stenocereus queretaroensis, Cactaceae)

Pitayos fStenocereus spp.) are columnar cacti that produce attractive edible fruits under both wild and cultivated conditions. Until recently the study of pitayos has been relatively neglected even though they have been a crucial staple for the inhabitants of subtropical semiarid lands of Mexico since ancient times and this century have become an important fruit crop there. The main objective of this review is to relate seasonal aspects of vegetative and reproductive growth, CO2 uptake, and carbohydrate resources to abiotic components of the environment. Flower and fruit production occur during the dry season in the late winter and spring, roots grow during the summer wet season, and stem elongation commences in the autumn at the beginning of the dry season. Vegetative growth thus does not coincide with reproductive growth, as it does for other fruit crops in temperate and tropical regions. The time offset of vegetative and reproductive activities reduces competitive sink effects, regulating assimilate partitioning to different organs, which may allow Stenocereus queretaroensis to adapt to water-limited environments. Reserve carbohydrates (starch, mucilage) accumulate in the early summer just after reproductive growth and in the early winter just after stem extension. Reducing sugars increase during the middle of the summer before stem elongation begins. The low rates of growth and of photosynthesis for S. queretaroensis are associated with low tissue levels of nitrogen, chlorophyll, and some micronutrients (Fe, Mn). Low levels of gibberellic acid may also contribute to its low growth rate. It does not respond morphologically to irrigation during the dry period, indicating a low plasticity for growth. Although S. queretaroensis is cultivated, its physiological and phenological activities closely resemble those of wild CAM species and other wild perennial plants, reflecting its rather recent domestication and the fact that selections were based mainly on fruit quality and adaptation to aridity rather than biomass productivity.

Surface measurements of formaldehyde and formic and acetic acids at a subtropical semiarid site in India

Vapor phase formaldehyde, formic acid, and acetic acid (HCHO, HCOOH, and CH3COOH) were measured at Dayalbagh, a suburban site in Agra. The average mixing ratios of formaldehyde, formic acid and acetic acid for the entire data set (N=60) were 0.8±0.5 parts per billion by volume (ppbv), 1.4±0.8 ppbv, and 0.9±0.3 ppbv, respectively. Maximum levels of HCHO were observed between 1500 and 1900 hours (LT) possibly because of an increase in in situ formation up to 1600 hours. The extension of maximum concentration up to 1900 hours was probably due to low rates of HCHO removal as a result of diminished insolation and a decrease in OH concentration. Formic and acetic acids showed elevated levels between 1000 and 1600 hours, probably due to active photochemistry and direct emissions. HCOOH and CH3COOH correlated significantly with each other but not with HCHO. This finding suggested the origin of both the acids from the same sources, while HCHO had different pathways. Rates of direct emission, in situ formation, and removal by dry deposition were estimated for both acids. In situ reaction produced more formic acid than acetic acid. Production of acetic acid was seen to be dominated by direct emissions. The production estimates exceed removal by a factor of ≈2.5; these fall within the uncertainty limits.

Global solar radiation, soil temperature and permafrost in the Central Andes, Argentina: A progress report

AbstractDuring various expeditions to the High Andes of Argentina at latitudes 30º and 33º south, extensive geomorphological investigations have been carried out. The subtropical semiarid climate is characterized by intense global radiation with peaks of more than 1400 W/m2 and daily sums of >39 MJ/m2. The daily amplitudes of the soil temperatures (≤25 cm depth) correlate with incoming radiation. Diurnal ranges of soil surface temperature (1 cm) usually exceed 45ºC, with maximum values of 55ºC at 4150 m a.s.l. Active rock glaciers exist above 4000 m a.s.l. and the thickness of the active layer varies from 1.4 to 2.5 m between 4000 and 4700 m a.s.l. Periglacial features (rock glaciers, thermokarst, gelifluction, etc.) are widespread. They are used as edaphic indicators for the lower limit of discontinuous permafrost, which is thought to be at an elevation of 4000 ± 200 m a.s.l.

THERMAL RELATIONS OF FIVE SPECIES OF TROPICAL LIZARDS

The relation of a reptile's body temperature to that of the surrounding environment has been of considerable interest since the work of Cowles and Bogert (1944), and Bogert (1949a). These authors demonstrated that by behavioral methods reptiles were able to maintain their body temperature within a relatively narrow range. Reptiles, in other words, were shown to exhibit a degree of homeostasis in regard to their body temperature. The preferred or eccritic body temperature, was not the same for all the species studied. However, Bogert (op. cit.) demonstrated that lizards belonging to the same genus have similar body temperatures, while there may be marked differences between genera. Virtually all work reported for lizards has been with basking (heliothermic, Cowles, 1940) forms that gain heat from radiant energy. These heliothermic species raise their temperature above that of the surrounding air, and may achieve differences as great as 31 ? C between their body temperature and that of the surrounding air (Strelnikov, 1944; Pearson, 1954). With few exceptions (Inger, 1959; Bogert, 1949b) the species that have been studied are all temperate region forms, and actually the most intensively studied species have been from semiarid regions. In this investigation five Cuban species of the neotropical iguanid genus Anolis were studied in the field to determine their body temperatures and habitat temperatures. Two of the species were also studied in the laboratory to augment the findings in the field. The five species presented an opportunity to study thermal relations in tropical reptiles. As St. Girons and St. Girons (1956) emphasize, little is known about the thermal relations of tropical reptiles. The tropics represent the zone of the greatest abundance of species and individuals of reptiles. This abundance is in part attributable to the narrow temperature fluctuations of the lowand tropics where the temperature extremes of temperate and subtropical semiarid areas are never encountered. These five Cuban species represent an extraordinary example of habitat differentiation between closely related species in contiguous habitats. At the localities studied in central Cuba all five species are present, yet each is segregated in a specific ecological niche. As will be described below, the habitats range from the deep shaded portions of the forests, to the margins of the forests where filtered sunlight is present, to the open exposed habitats of the pastures and savannas.