Temporal and spatial patterns of tenebrionid beetle diversity in NW Patagonia, Argentina

Spatial and temporal variation in abundance, richness and composition of Tenebrionidae beetle assemblages were described for north-western Patagonia. Beetles were collected using 450 pitfall traps arranged in 50 plots across an area of about 22,500 km² representative of the Subantarctic-Patagonian transition of Argentina. The study area included three different habitats: forest, scrub, and steppe. Beetles were trapped at five, eight day sampling periods in spring-summer between November 2004 and March 2006. A total of 30 species and 938 individuals were collected. Total abundance was higher in November and January than in March, and species richness did not change among samplings. Species richness was greater in the steppe than scrub. Assemblages differed between the northern and southern transects. There was little correlation between the measured environmental variables and species composition. Historical factors might explain the observed patterns, but other environmental variables such as soil characteristics may be more informative in explaining the present distribution of tenebrionid species.     

Structural and nutritional heterogeneity of riparian vegetation in Patagonia (Argentina) in relation to seasonal grazing by sheep

Riparian meadows of southern Patagonia are temporally and spatially heterogeneous habitats. They are thought to play a key role in regulating the dynamics of arid grazed steppes of the region. We conducted a 2-year study with sheep to determine the influence of two grazing conditions (deferment and spring grazing) on structural and nutritional parameters of three vegetation types apparently associated with a soil moisture gradient in a riparian meadow in southern Santa Cruz (Argentina). Spring deferment allowed forage accumulation in very moist and intermediate vegetation types by the beginning of the summer and had no detrimental impact on forage quality. Deferment had no effect on biomass accumulation of the drier vegetation type at our study site. Structural attributes of the vegetation appeared to affect spatial grazing patterns of sheep. Soil-related patchiness, rather than sheep grazing, appeared to control vegetation structure and nutritional value. The proportion of more mesic plant communities in riparian habitats of Patagonia could determine the outcome of plant–animal interactions in these systems. Practical recommendations of grazing capacity in paddocks, or more theoretical considerations of ecosystem dynamics of the Patagonian steppes need to explicitly consider the internal patchiness of riparian habitats.     

天山北坡三工河流域中山带森林发育与气候土壤的关系

开展干旱区山地森林发育状况及其土壤因素影响的分析,对干旱区乃至全球山地森林带的成因研究具有重要的理论意义。以天山北坡三工河流域为研究区,主要利用森林调查与遥感影像数据,确定该流域森林带的分布状况,并结合流域气象与土壤采样数据,重点分析气候土壤因素对森林发育的影响。结果表明:1.该流域森林带位于海拔1 510～2 720 m,胸径与树高随海拔增加呈双峰曲线;其中胸径两个峰值分别位于约海拔2 000 m与2 550m,而树高峰值分别为海拔2 100 m与2 600 m,均稍高于胸径的峰值海拔高度;2.在森林带内,年均温随海拔高度增加呈线性下降趋势,最冷月均温(1月)则表现先增加后减小趋势;与其他地区相比,该流域高山林线年均温较高,最冷月均温相差较大,而最热月均温差异不明显;年降水量呈先增加后减小的趋势,且在海拔2 000 m左右达到最大值。土壤属性随海拔递增呈规律性的变化趋势:森林带内海拔约2 000～2 700 m树木发育较好,其有机质、全磷及全氮含量较高;CaCO3,pH值及电导率最小值与海拔2 000 m的最大降水带恰好吻合;土壤A层(0～10 cm)有机质、全磷及全氮含量与B(10～30 cm)、C(>3...     

Selective erosion of clay,organic carbon and total nitrogen in grazed semiarid rangelands of northeastern Patagonia,Argentina

In arid and semiarid rangelands, soil erosion has been widely considered an important soil degradation process and one of the main factors responsible for declining soil fertility. In this study, we determined the sediment production and the enrichment ratios of clay, organic C, and total N by using rainfall simulations on runoff plots (0.60 × 1.67 m) in three plant communities of northeastern Patagonia: grass (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS). Our results clearly indicate that spatial variability in soil loss rate and enrichment process exists as a result of the local differences in both plant composition and soil surface characteristics. Sediment production was significantly lower in the GS (14.2 g m⁻²) compared with the DGS and DSS (38.2 and 51.5 g m⁻², respectively). In the GS, the enrichment ratio of clay was significantly greater (3.9) and enrichment ratio of organic C was lower (3.1) than in the DGS and the DSS, though differences in enrichment ratios of total N were not significant. The high rate of soil loss and nutrients through overland-flow may limit the opportunities that promote the pathway from DGS back to GS community, favoring the dominance of shrubs.     

Traditional horticultural and gathering practices in two semi-rural populations of Northwestern Patagonia

Horticultural and gathering practices were studied in Comallo and Pilcaniyeu, two semi-rural communities which share a common Mapuche ancestry and occupy similar arid environments in Northwest Patagonia, Argentina. We analyzed cultivation and wild plant gathering using semi-structured interviews. We hypothesized that these activities will be conditioned by access to market economy. Results showed differences in horticultural and gathering patterns in both populations: the community with less access to market economy presented greater richness of cultivated and gathered species and collected more seeds from their own harvests, thus promoting germplasm conservation and higher levels of seed exchange than the community that had more contact with urban centers. In these populations the integration of ancestral and novel knowledge seems to favor flexibility and autonomy, which might help locals deal with change. This could foster greater individual and collective wellbeing, as well as socio-ecological diversity.     

Structural and nutritional heterogeneity of riparian vegetation in Patagonia (Argentina) in relation to seasonal grazing by sheep

Riparian meadows of southern Patagonia are temporally and spatially heterogeneous habitats. They are thought to play a key role in regulating the dynamics of arid grazed steppes of the region. We conducted a 2-year study with sheep to determine the influence of two grazing conditions (deferment and spring grazing) on structural and nutritional parameters of three vegetation types apparently associated with a soil moisture gradient in a riparian meadow in southern Santa Cruz (Argentina). Spring deferment allowed forage accumulation in very moist and intermediate vegetation types by the beginning of the summer and had no detrimental impact on forage quality. Deferment had no effect on biomass accumulation of the drier vegetation type at our study site. Structural attributes of the vegetation appeared to affect spatial grazing patterns of sheep. Soil-related patchiness, rather than sheep grazing, appeared to control vegetation structure and nutritional value. The proportion of more mesic plant communities in riparian habitats of Patagonia could determine the outcome of plant–animal interactions in these systems. Practical recommendations of grazing capacity in paddocks, or more theoretical considerations of ecosystem dynamics of the Patagonian steppes need to explicitly consider the internal patchiness of riparian habitats.     

我国半干旱地区土壤的特性与可持续发展

我国年降水量250~ 450mm的半干旱地区,主要发育有栗钙土、淡黑垆土、黑麻土、黄绵土和灰钙土。前四者具有半干润土壤水分状况,后者存在干旱土壤水分状况。贫乏的土壤水分状况与区内的光热资源匹配不协调,限制了天然乔木林的正常生存,制约了农业的不稳定,但却适宜耐旱灌木和耐旱禾草植物生长。因此,区内可持续发展:一要发展水利,二要建造水平梯田,三要根据土壤适生耐旱草灌植物的特性,在发展农业的同时,扩大发展草业、饲养业、畜产品深加工业。     

黑河下游五种不同植被类型土壤呼吸的差异性解析

土壤呼吸的微小变化会对大气CO₂浓度产生重大影响,尤其在极端干旱区。通过对黑河下游额济纳旗四道桥的混合林、胡杨、柽柳、农田及裸地的土壤呼吸进行研究,结果表明：2014 年夏季5 种不同植被类型的土壤呼吸速率大小排序：胡杨柽柳混合林 > 柽柳 > 农田 > 胡杨 > 裸地,各类型的5 cm处土壤温度和湿度无明显变化规律,土壤温度在22～35 ℃,土壤湿度集中在13%～61%的变化范围。探究了5 种不同植被类型的土壤呼吸速率与土壤温度、土壤湿度、地表温度、空气温度及空气湿度的线性相关关系,发现它们的土壤呼吸速率与土壤温度、土壤湿度、空气温度、空气湿度之间无显著相关（P>0.05）,表明水热因子对土壤呼吸的影响具有很大的不确定性。     

Diatom-based reconstruction of Holocene hydrological changes along the Colorado River floodplain (northern Patagonia,Argentina)

Diatom assemblages recovered from a Colorado River delta core in northern Patagonia, Argentina were analyzed in order to assess past environmental conditions. A total of 35 samples were selected from a 172-cm core extracted 37 km from the mouth (39°36′19.6″S; 62°29′26.1″W). One-hundred and thirty-eight taxa were recognized and grouped according to life forms. Two diatom zones were identified by cluster analysis. At the base of the sequence, the Diatom Zone I (DZI; 4132 ± 35 ??2919?±?27 ¹⁴C yr BP), consisted of clays, and was characterized by assemblages dominated by aerophilous and benthic taxa and chrysophyte stomatocysts, which led to inferences of a sedimentary environment corresponding to a pond experiencing dry periods. The upper section (DZII) was dominated by fine sands and silts encompassing the last ~?150 yr with abundant planktonic and tychoplanktonic diatoms. Benthic diatoms were abruptly replaced by planktonic forms in this zone indicating a shift to deeper waters. These results characterize the meandering dynamics of a deltaic system. During the Mid-Holocene, more arid periods would have favored the deactivation of meanders and the formation of riverine and oxbow wetlands. In Late-Holocene and historical times, more humid conditions and the hydrological system across the floodplain reactivated the paleochannel. Today, the dominant diatom species are brackish/freshwater fragilaroids. A non-multidimensional scaling analysis showed a lack of analogy between fossil and modern samples. The change in diatom floras in recent historical times was attributed to anthropogenic disturbances, a consequence of the regulation of the river flow. This regulation is evidenced by less discharge, morphological modifications in the floodplain and increased salinity in the last decade.     

Traditional horticultural knowledge change in a rural population of the Patagonian steppe

We investigated traditional horticultural knowledge related to plant species cultivated in homegardens in an arid rural population of North-western Patagonia, Argentina. By means of semi-structured interviews and field visits to the cultivated areas we analyzed floristic composition and structure of: vegetable-gardens, greenhouses and gardens. We evaluated species richness, cover and biogeographical origin in each cultivated area and analyzed the influence of socio-cultural factors, such as age and gender, on informants’ cultivation practice. A total of 124 species was found: 75 species in vegetable-gardens, 63 in greenhouses and 68 in gardens. In all cultivated areas, most plant species (91%) were exotic and mainly used for edible purposes. Plant richness in homegardens increased with informants’ age and both men and women play a relevant role in the maintenance of cultivated areas. Traditional knowledge in this community has been suffering an erosion process, which is in part influenced by the intervention of extension agents. However, their presence creates the possibility of integrating new and ancestral practices, favoring development of knowledge of a hybrid, syncretic nature. Alongside these changes, Pilcaniyeu inhabitants still maintain traditional homegardens cultivation, through which we can appreciate the intricate relationship between people and their physical, historical, cultural and spiritual contexts.     

Realistic soil C sink estimate in dry forests of western Argentina based on humic substance content

Due to high temporal variation of soil organic matter in arid regions, estimates of annual sequestered C might be overestimate. We assessed the soil stable organic matter (humic substances) in the transitional area between Dry Chaco and Monte eco-regions in western Argentina, as an approach to estimate realistic soil C sink. Soil samples were taken during wet and dry seasons in four sites along precipitation gradient. In each site three soil cover situations (under tree, under shrubs and on bare soils) were sampled (n = 5) and the quantity and type of residues (tree and shrub leaves, woody material, grasses and forbs) were recorded. Soil organic matter and humic substances (humic and fulvic acids) content were analyzed and non-humic substances were calculated by the differences between organic matter and humic substances. Soil humic substance proportion respect to SOM was low (20%) in all sites and it did not correspond with the precipitation gradient. Non-humic substances were lower in wet season indicating high C lability. The most important factors that affected soil humic substance content were the type and quantity of organic residues and soil cover type. Our results suggest that previous C sink estimations in Argentina dry forest probably are overestimated.     

基于改进型TVDI在干旱区旱情监测中的应用研究

干旱是全球范围内影响最为广泛的自然灾害之一,其所导致的土壤沙漠化、荒漠化和盐碱化给生态环境造成不可逆的危害。通过对MODIS数据进行投影转换、去云等预处理的基础上,利用地形校正对TVDI模型进行改进,构建了改进型的温度植被干旱指数（mTVDI）用于新疆干旱区旱情监测。利用土壤实测数据对mTVDI及传统的TVDI模型进行对比验证。研究结果表明：（1） 利用EVI与校正后的LST构建的mTVDI_E对干旱区旱情的敏感度最高,与实测土壤水分数据的相关性R²为0.74。（2） 从空间上看,新疆2015年旱情分布以塔里木盆地和准噶尔盆地为两个干旱中心,旱情状况由严重逐步向周围山区递减至湿润状态。从时间上看,新疆6月、7月和8月旱情最为严重。（3） 研究利用TRMM降水数据对基于mTVDI_E反演的新疆旱情时空分布特征进行对比分析,结果表明二者所表现出的旱情时空分布较为一致,不同时间段内的降水量与mTVDIE之间具有一定的相关性,且均通过了P<0.01显著性检验。综上,基于TVDI所提出的mTVDI_E 能够有效开展新疆干旱区旱情监测,且精度较高,从而为今后定量化开展大区域尺度旱情监测研究提供参考。     

Spatial Patterns in Surface Energy Balance Components Derived from Remotely Sensed Data

A relatively simple modeling approach for estimating spatially distributed surface energy fluxes was applied to two small watersheds, one in a semi‐arid climate region and one in a sub‐humid region. This approach utilized a combination of ground‐based meteorological data and remotely sensed data to estimate ‘instantaneous’ surface energy fluxes at the time of the satellite or aircraft overpasses. The spatial resolution in the watershed grid cells, which was on the order of 100‐400 km, was selected to be compatible with ground measurements used for validation. The model estimates of surface energy fluxes compared well with ground‐based measurements of surface flux (typically within approximately 40 Wm^?2). The model accuracy may be slightly less for bare soil surfaces due to an overestimation of the soil heat flux. In addition to demonstrating the feasibility of computing spatially distributed values of surface energy fluxes, these maps were used to qualitatively infer the dominant factors controlling the energy fluxes for the time period shortly following precipitation events in the basins. For the semi‐arid watershed, values of sensible heat flux varied considerably over the watershed and displayed a pattern very similar to that of the spatially variable cumulative precipitation for at least one to eight days prior to the image acquisition. Due to the large fraction of exposed bare soil in a semi‐arid ecosystem, even very small precipitation events had a strong influence on the pattern of sensible heat fluxes observed shortly after the event (less than 24 hours). For the sub‐humid watershed, the fluxes tended to be more uniform across the watershed, and were influenced by a combination of precipitation total and land cover type.     

Patterns of alien plant invasions in northwestern Patagonia, Argentina

Invasive plant species are a growing concern in many regions of the world, yet little information is available on the effects of habitat type and distance to urban settlements on the ability of alien plants to become established. We studied plant communities from the arid steppes to the Andean forest within two national parks and surroundings, in northwestern Patagonia, Argentina. Alien and native vascular plant species were sampled using 90 × 100 m² plots and analyzed in relation to both climatic and environmental variables and distance to urban centres. We also compared life-forms of alien and native species. Precipitation and distance to an urban centre were important determinants of alien species community richness and composition, and shrubland sites had significantly more alien species than forest or steppe sites. Alien flora (15% of the species) was composed of a higher proportion of annuals and biennials than native flora. Our results suggest that precipitation, distance to source population, and anthropogenic disturbance influence the invasion process in this region, together with the availability of open niches. This work stresses the importance of monitoring invasive species in natural reserves, and of considering habitat types as well as idiosyncratic characteristics of the non-natives for developing management strategies.     

Soil fertility evolution and landscape dynamics in a Mediterranean area: a case study in the Sant Llorenç Natural Park (Barcelona, NE Spain)

The cartography of land covers was used to study fertility and soil evolution in a mountainous Mediterranean area during the anthropocene period ( Crutzen P J 2002 Geology of mankind Nature 415 23). The aim was to determine changes in fertility as agricultural lands were abandoned in the 14 000 hectare area that constitutes Sant Llorenç del Munt Natural Park in a pre-coastal Catalan mountain range (north-eastern Iberian Peninsula). The analysis of land covers using vegetation maps, orthorectified images and aerial photography has allowed us to differentiate six vegetation groups: holm-oak wood, pine grove, oak wood, scrub, active agricultural fields and abandoned agricultural fields. The anthropic covers over the past 100 years were subdivided into five categories: active fields and those abandoned over four time periods. Study variables include field shape (concave, convex, flat), orientation (north, south) and slope (ranging from 12º to 24º). The parameters used for the physical-chemical soil analysis included organic material, phosphorous and potassium; fertility was classified based on groups, types and classes. The results indicate that even when the visual appearance of certain landscapes is similar, the edaphic characteristics may be very different. Changes induced by human disturbance share this phenomenon. Therefore, land management should be considered globally, taking into account vegetation, soils and water as interdependent factors, since it is their interaction that produces landscape and most affects its evolution over time.     

LAND DEGRADATION AND ITS MANAGEMENT IN THE ARID AND SEMI ARID AREAS OF CHINA

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Relationships between Trophic State, Paleosalinity and Climatic Changes during the First Holocene Marine Transgression in Rocha Lagoon, Southern Uruguay

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using a sediment core that extended from 7000 to about 3700 yr BP, analyses of organic matter, carbonate, diatoms and chrysophyte cysts were used to track the early Holocene paleolimnological conditions of Rocha Lagoon. Opal phytoliths were also counted and identified, both temperature and humidity indices were calculated, and Opal Phytolith Association Zones (OPAZ) were identified by performing Principal Coordinates Analysis (PCO). Diatom Association Zones (DAZ) corresponding to marine/brackish and brackish/freshwater episodes were closely related to changes in trophic state. Those DAZ representing marine/brackish stages exhibited a lower trophic state than those DAZ dominated by brackish and freshwater diatoms. This highlights that during the first Holocene marine transgression, Rocha Lagoon did not continuously exhibit marine/brackish conditions as reported in previous papers. Instead, three brackish/freshwater episodes related to sea level variation and changes in humidity were identified. The first episode, by ~6000 yr BP, was related to sea level change as no significant changes in either temperature or humidity indices were observed. The second episode, between 5000 and 4400 yr BP, was related to both a sea level decrease and an increase in humidity, as a transition from humid to very humid climate was inferred. Concomitant decreases in salinity and increases in trophic state were also observed. The third episode, after ~4000 yr BP, was related to the end of the first Holocene regressive phase when sea level was slightly below present levels. Further decreases in salinity and increases in trophic state were detected. The paleoclimatic trends inferred in this study were in close agreement with other regional studies on climatic change, as cool temperatures were inferred. However, major changes in humidity were also detected. A humid to very humid climate was inferred for ~7000–4500 yr BP, but the occurrence of a semiarid/arid climate was inferred for ~4500–3700 yr BP. Our data suggest that during transgressive and regressive events there might be higher frequency and lower amplitude sea level oscillations that might lead to changes in salinity and trophic state of coastal aquatic systems. Such oscillations could only be tracked by high resolution analyses of sedimentary records and could be best interpreted with complementary data on paleoclimate. In addition, microfossils such as diatoms and opal phytoliths were shown to be very sensitive to such paleoenvironmental changes.     

Variability and management patterns of range resources in the Baro River plain, Ethiopia

The biophysical environment of rangelands in the arid and semi-arid lowland parts of Africa is customarily viewed as a homogenous entity. Such notion has encouraged employing a blanket management approach. However, there are perceptible variations within them which necessitate site-specific range management. This study has attempted to identify the variability of soil and forage attributes and assess the existing management practices of those resources in the Baro River plain, Ethiopia. Sample transects, representing pre- and post-fire conditions, were used to collect composite soil samples and vegetation attributes. Alongside the physical survey, a household survey was undertaken to validate the laboratory-generated information. The result showed significant differences of soil and forage attributes among different management regimes, distances from river course and dominant cover types. In general, the distribution of soil nutrients showed a 'distance decay effect', while the distribution of pH showed the reverse pattern. Application of heavy fire load and congested grazing are the principal range management related factors. About 80 per cent of sample pastoralists employ heavy fire without due consideration for the sustainability of the range resource and without considering the local variability. Recognition of site-specific information is the key to effective management of range resources in the study area.     

Changes in vegetation structure induced by domestic grazing in Patagonia (Southern Argentina)

We analyzed the structural differences associated with grazing exclusion on vegetation by studying 24 grazed-ungrazed paired sites in Patagonia (Argentina). Our objectives were to evaluate the effect of grazing on plant species composition, plant diversity, the relative abundance of plant functional types, and the vertical and horizontal structure of the plant community. This study across the shrub-grass steppes of Patagonia highlights some important characteristics of the vegetation response to a major disturbance factor we show that shrub encroachment is not a generalized response of the steppe to grazing. Grazed areas presented lower richness and diversity than exclosures. Physiognomic changes (as describe by relative abundance of plant functional types) were less important than those observed at the species level. These results shown that the status of the shrub-grass steppes of the Occidental district of Patagonia can not be characterized in terms of contrasting physiognomic states as in the case of the grass steppes of the Subandean district. Forbs and a few mesophytic and xerophytic grasses are the key elements to identify the condition of the steppe. Monitoring programs should focus on the relative abundance of these components.     

塔里木盆地绿洲蒸散量的日变化规律分析

根据蒸发的日变化过程，可以分析气候因子和下垫面状况对蒸发的影响程度和规律，本文通过中国科学院阿克苏水平衡试验结果的观测实验，和我国甘肃省沙坡头、山东省禹城县、日本筑波市的一些干旱、半干旱及湿润地区的蒸发日变化过程进行了对比分析，论述了干旱区蒸发日变化的一些特点。