Is the analysis of plant community structure better than common species-diversity indices for assessing the effects of livestock grazing on a Mediterranean arid ecosystem?

Grazing in arid Mediterranean ecosystems brings about changes in species diversity, but the best way to measure such changes is unclear. In this study we compared various methods in order to identify indicators that might be useful for the management and conservation of grazed arid Mediterranean ecosystems.Changes in community structure and composition were compared along a previously studied grazing gradient in Cabo de Gata-Nijar Natural Park. Plant diversity was measured by calculating diversity (Shannon information index), evenness (Pielou index) and richness (species number). Rarefaction curves were used to measure plant species richness and the results were compared with traditional richness values. Community structure was measured as the percentage of bare ground and the coverage of overall perennial grasses, Stipa tenacissima L., perennial shrubs and annual plants. Our results showed that the proportion of bare ground, the cover of perennial shrubs and the relative abundance of S. tenacissima are good indicators of grazing effects on vegetation. Overall plant community structure was more sensitive to the grazing gradient than were the diversity indices. Finally, the adequacy of standardized methods for comparing species richness (i.e. rarefaction curves) along a grazing gradient are discussed.     

沙冬青植物群落研究

沙冬青植物群落是中国沙漠地区特有的常绿植物群落，分布在荒漠区东部及荒漠草原地区。１９９１年在沙坡头地区北部的腾格里沙漠沙葱湾－通湖山一带发现有大片分布，面积达７１３３ｈａ。沙冬青植物群落的建群种沙冬青是第三纪古老的残遗种，我国已将它列入第一批珍贵稀濒危保护植物。不仅在科学研究上具有特殊意义，而且其耐旱性强，是沙漠及黄土地区适宜的防风固沙及水土保持林种，也可用作花卉，值得大力推广。     

Plant macroscopic remains from recent sediments of Banks Island,Northwest Territories,and Bathurst Island,Nunavut, Canada,and the interpretation of Quaternary cold stage plant macroscopic assemblages

Macroscopic plant remains were extracted from recent sediments of streams on Banks Island and Bathurst Island. Analyses of the samples are given and their general relation to the vegetation is described. Problems of interpretation of the contemporary and Quaternary cold stage macroscopic assemblages include the variation of the representation of taxa, the significance of taphonomy, especially under fluvial conditions, and the origin of the assemblages in a mosaic of vegetation. The contribution of analyses of macroscopic remains to interpretations of vegetation and environment based on pollen analysis is emphasised. Copyright © 2000 John Wiley & Sons, Ltd.     

Sources of organic matter in surface sediments of the Louisiana Continental margin: Effects of major depositional/transport pathways and Hurricane Ivan

Lignin and pigment biomarkers were analyzed in surface sediments of the Louisiana Continental margin (LCM) to distinguish differences in the degradative state of sedimentary organic matter along and between two major depositional pathways (along shore and offshore to the Mississippi Canyon) from Southwest (SW) Pass in July 2003. Barataria Bay, an inter-distributary estuary, was also assessed as a potential source of terrestrial organic matter to the LCM. Sediment signatures taken along the same pathways after Hurricane Ivan (October 2004) were compared with the pre-Ivan signature to elucidate carbon dynamics after major hurricane events. Density fractions were investigated at key stages across the LCM. Mississippi Canyon sediments are a depocenter for labile and refractory organic matter derived from river and previously deposited shelf sediments. Barataria Bay material may be a contributing source of sedimentary organic matter in shallow shelf areas bordering the bay and is thus potentially important in carbon cycling in sediments of these shallow areas; however, our results show that organic matter inputs from the bay were likely rapidly decomposed and/or diluted. Hurricane Ivan mobilized sedimentary organic carbon (SOC) offshore and homogenized terrestrial sediment parameters and gradients. As observed through pigment concentrations sediments tended to equilibrate to a more steady-state condition within months of the disturbance. Insights from density fractions show that selective degradation and aggregation/flocculation processes were also very important processes during cross-shelf transport. Zooplankton grazing, largely on diatoms and other algae, was a shelf wide phenomenon, however, grazing products dominated the marine-derived SOC in margin sediments west of the birdsfoot delta indicated by the abundance of steryl chlorin esters (SCEs).     

Pliocene flora and paleoenvironment of Zanda Basin,Tibet, China

This paper describes a plant megafossil assemblage from the Pliocene strata of Xiangzi, Zanda Basin in the western Qinghai-Tibet Plateau. Twenty-one species belonging to 12 genera and 10 families were identified. Studies show that the Pliocene vegetation in Zanda Basin was mostly deciduous shrub composed of Cotoneaster, Spiraea, Caragana, Hippophae,Rhododendron, Potentilla fruticosa, etc. Leaf sizes of these taxa were generally small. Paleoclimate reconstruction using Coexistence Analysis and CLAMP showed that this area had higher temperature and precipitation in the Pliocene than today, and distinct seasonal precipitation variability was established. The reconstructed paleoelevation of Zanda Basin in the Pliocene was similar to modern times. In the context of central Asian aridification, the gradual drought in the area beginning in the late Cenozoic caused vegetation to transition from shrub to desert, and the flora composition also changed.     

Long-term perspective on the relationship between phytoplankton and nutrient concentrations in a southeastern Australian estuary

Sixteen years (1997–2013) of physicochemical, nutrient and phytoplankton biomass (Chlorophyll-a (Chl-a)) data and a decade (2003-2013) of phytoplankton composition and abundance data were analyzed to assess how the algal community in a temperate southeastern Australian estuary has responded to decreased chronic point source nitrogen loading following effluent treatment upgrade works in 2003. Nitrogen concentrations were significantly lower (P < 0.05) following enhanced effluent treatment and Chl-a levels decreased (P < 0.05) during the warmer months. Temperature and nutrient concentrations significantly influenced temporal changes of Chl-a (explaining 55% of variability), while salinity, temperature, pH and nutrient concentrations influenced phytoplankton abundance and composition (25% explained). Harmful Algal Bloom (HAB) dynamics differed between sites likely influenced by physical attributes of the estuary. This study demonstrates that enhanced effluent treatment can significantly decrease chronic point source nitrogen loading and that Chl-a concentrations can be lowered during the warmer months when the risk of blooms and HABs is greatest.     

Organochlorine contaminants in endangered Hawaiian monk seals from four subpopulations in the Northwestern Hawaiian Islands

We analyzed blubber and blood samples for organochlorines (OCs) from 158 Hawaiian monk seals (Monachus schauinslandi) at four of their six primary breeding colonies in the Northwestern Hawaiian Islands. Levels of OCs in blubber were lower in adult females compared to juveniles or adult males, evidently owing to the transfer of these lipophilic compounds to pups by pregnant and lactating females. Concentrations of SigmaPCBs and p,p'-DDE in blubber generally increased with age until seals were sexually mature and then continued to increase with age in males after puberty. Average levels of PCBs and PCB toxic equivalents (TEQs) in blubber were significantly higher in adult male and juvenile seals at Midway Atoll than the same age class of seals at the other colonies. Unlike concentrations of OCs in blubber, circulating levels of OCs in blood did not vary consistently among age classes of seals or among breeding colonies. Though the concentrations of OCs measured in Hawaiian monk seals were generally equal to or lower than those reported for other pinniped species in the North Pacific Ocean, they were high enough in a few seals to potentially affect their health.     

Hydrocarbon micro-seepage detection from airborne hyper-spectral images by plant stress spectra based on the PROSPECT model

Hydrocarbon micro-seepage can result in vegetation spectral anomalies. Early detection of spectral anomalies in plants stressed by hydrocarbon micro-seepage could help reveal oil and gas resources. In this study, the origin of plant spectral anomalies affected by hydrocarbon micro-seepage was measured using indoor simulation experiments. We analyzed wheat samples grown in a simulated hydrocarbon micro-seepage environment in a laboratory setting. The leaf mesophyll structure (N) values of plants in oil and gas micro-seepage regions were measured according to the content of measured biochemical parameters and spectra simulated by PROSPECT, a model for extracting hydrocarbon micro-seepage information from hyper-spectral images based on plant stress spectra. Spectral reflectance was simulated with N, chlorophyll content (C_ab), water content (C_w) and dry matter content (C_m). Multivariate regression equations were established using varying gasoline volume as the dependent variable and spectral feature parameters exhibiting a high rate of change as the independent variables. We derived a regression equation with the highest correlation coefficient and applied it to airborne hyper-spectral data (CASI/SASI) in Qingyang Oilfield, where extracted information regarding hydrocarbon micro-seepage was matched with known oil-producing wells.     

Effects of age, sex and reproductive status on persistent organic pollutant concentrations in “Southern Resident” killer whales

“Southern Resident” killer whales (Orcinus orca) that comprise three fish-eating “pods” (J, K and L) were listed as “endangered” in the US and Canada following a 20% population decline between 1996 and 2001. Blubber biopsy samples from Southern Resident juveniles had statistically higher concentrations of certain persistent organic pollutants than were found for adults. Most Southern Resident killer whales, including the four juveniles, exceeded the health-effects threshold for total PCBs in marine mammal blubber. Maternal transfer of contaminants to the juveniles during rapid development of their biological systems may put these young whales at greater risk than adults for adverse health effects (e.g., immune and endocrine system dysfunction). Pollutant ratios and field observations established that two of the pods (K- and L-pod) travel to California to forage. Nitrogen stable isotope values, supported by field observations, indicated possible changes in the diet of L-pod over the last decade.     

油蒿群落植物多样性动态

油蒿为鄂尔多斯高原植被的优势种和建群种,油蒿群落的植物多样性有向顶极阶段增加的趋势。植物多样性的季节变化与气候的季节变化密切相关。人类活动特别是过度放牧,引起油蒿群落的退化,导致植物多样性降低。围育可使退化的油蒿群落向正向演替进行,使群落的植物多样性提高。