Effects of alleviation of ecological stresses on an alpine tundra community over an eight-year period

Alpine tundra ecosystems such as those which are dominated by ericaceous dwarf shrubs in northern Scandinavia are characterised by low productivity, and this is due in part to low availability of nutrients and retardation of those microbial processes required for nutrient cycling. We conducted an eight‐year field experiment in an alpine tundra in northern Sweden, in which eleven treatments aimed at alleviating possible stresses were applied to field plots; these included addition of various forms of nitrogen and other nutrients, addition of lime, addition of available carbon, and reduction of possible adverse effects of secondary metabolites produced by the dwarf shrub Empetrum hermaphroditum. Nearly all of the treatments had statistically significant effects on at least some of the plant species present in the experiment. Addition of nitrogen and liming both had important effects in reducing E. hermaphroditum cover and in these treatments Deschampsia flexuosa rapidly became dominant. Manipulations that reduced E. hermaphroditum or its effects frequently also stimulated Vaccinium myrtillus and V. vitis‐idaea. Fertilisation and liming treatments also often caused decreases in the mosses Dicranum sp. and Pleurozium schreberi, and the lichen Cladina spp. Ordination analysis revealed that vascular plant community structure was most significantly altered by treatments involving mineral nitrogen addition and liming, moss community structure by treatments involving addition of available carbon and lichen community structure by treatments involving addition of some forms of nitrogen, lime and reduction of effects of E. hermaphroditum. Nearly all treatments significantly reduced total plant diversity (species richness) and several treatments reduced diversity of each of the vascular plant, lichen and moss groups. This reduction in diversity was frequently associated with monopolisation of plots by D. flexuosa. Decomposition rates of litter added to the plots were generally only weakly influenced by treatments, but several treatments (most notably those involving nitrogen addition) induced litter nitrogen immobilisation and increased litter microbial biomass levels. Humus nitrogen and microbial levels were also sometimes enhanced by the nitrogen addition treatments. This suggests that those plots dominated by D. flexuosa were likely to result in greater conservation of nitrogen in the litter relative to those dominated by E. hermaphroditum. An important exception to this pattern was the effects of the liming treatment which, although responsible for an increase in D. flexuosa, caused net losses of nitrogen and reduced microbial biomass both in the litter and the humus. Our data therefore suggest that treatments which have vastly differing consequences for humus properties and the decomposer subsystem (and ultimately conservation of nitrogen in the soil), but which alleviate an inherent stress, have similar consequences above‐ground, e.g. E. hermaphroditum decline, D. flexuosa enhancement, and associated reductions of plant diversity.     

Selection of alpine grasslands over beech forest by stoats (

Predation by introduced stoats is now considered a major threat to the population viability of several New Zealand endemic bird species. Historically stoat research and management has focused on beech forests and little is known about the ecology of stoats in the alpine grasslands occurring above the natural altitudinal limit of beech forest. Several stoat control operations in beech forest valley floors in southern New Zealand assume that adjacent montane areas act as a barrier to stoat immigration. Stoats were live-trapped and radio-tracked in alpine grasslands above the Borland Burn, Fiordland National Park, during the summer and autumn of 2003 and 2004. Seventeen stoats were radio-collared and home ranges were estimated for 11 of them. These home ranges were used in a compositional analysis which showed that these stoats spent significantly more time in alpine grassland than in adjacent beech forest. Range cores calculated for six of these stoats were located high up in alpine grassland and contained very little beech forest. This means that montane areas that contain alpine grasslands are unlikely to be barriers to stoat immigration; rather they may be a source of dispersing stoats that reinvade control areas. Also, endemic animal species that inhabit alpine grasslands could be at risk from stoat predation.     

草原土壤有机碳含量的控制因素

基于374个高寒草原和温带草原土壤样品的测试结果,运用多元逐步回归分析模型定量评估了土壤环境因子对土壤有机碳(SOC)含量的影响.结果表明:高寒草原土壤有机碳含量(20.18 kg C/m2)高于温带草原(9.23 kg C/m2).土壤理化生物学因子对高寒草原和温带草原SOC含量(10 cm)变化的贡献分别是87.84％和75.00％.其中,土壤总氮含量和根系对高寒草原SOC含量变化的贡献均大于对温带草原SOC含量变化的相应贡献.土壤水分是温带草原SOC含量变化的主要限制性因素,其对SOC含量变化的贡献达33.27％.高寒草原土壤C/N比显著高于温带草原土壤的相应值,揭示了青藏高原高寒草原较高的SOC含量是由于较低的土壤微生物活性所导致.     

Greenhouse gas fluxes over managed grasslands in Central Europe

Central European grasslands are characterized by a wide range of different management practices in close geographical proximity. Site‐specific management strategies strongly affect the biosphere–atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO₂ exchange, while long‐term N₂O and CH₄ flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO₂, N₂O, and CH₄ fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO₂ sink (−1,783 to −91 g CO₂ m⁻² year⁻¹), but a N₂O source (18–638 g CO₂‐eq. m⁻² year⁻¹), and either a CH₄ sink or source (−9 to 488 g CO₂‐eq. m⁻² year⁻¹). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between −2,761 and −58 g CO₂‐eq. m⁻² year⁻¹, with N₂O and CH₄ emissions offsetting concurrent CO₂ uptake by on average 21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with ploughing. The predictive power of soil parameters for N₂O and CH₄ fluxes was generally low and varied considerably within years. However, after site‐specific data normalization, we identified environmental conditions that indicated enhanced GHG source/sink activity (“sweet spots”) and gave a good prediction of normalized overall fluxes across sites. The application of animal slurry to grasslands increased N₂O and CH₄ emissions. The N₂O‐N emission factor across sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1%–8.6%). Although grassland management led to increased N₂O and CH₄ emissions, the CO₂ sink strength was generally the most dominant component of the annual GHG budget.     

Development of vegetation and environmental conditions in an oligotrophic Danish lake over 40 years

1. Oligotrophic ‘Lobelia-lakes’ are rare in Denmark. The few that have survived widespread eutrophication are in uncultivated sandy regions and are threatened by acidification and increased nutrient deposition from the atmosphere. Grane Langsø was considered the clearest lake in Denmark in the 1950s, when isoetids grew to 5.5 m depth and characeans covered the deepest part of the lake bottom at 11.5 m. The goal of the study reported here was to examine whether the lake has maintained this high quality by studying the development of macrophyte distribution and composition in relation to the changes in pH, nutrient conditions and transparency over the past 40 years. 2. Aquatic mosses now dominate the vegetation rather than rooted isoetids, probably as a result of acidification (summer median pH was 5.60 in 1958–1963 compared to 5.07 in 1976–1994). Along with a reduced median pH, annual pH fluctuations have increased from about 0.3 units 40 years ago to 0.9 units today. 3. The depth limit of isoetid species has declined markedly and Nitella flexilis, which previously dominated the dense bottom vegetation in the hypolimnion, has disappeared. These changes can be accounted for by reduced light penetration and an increased cover of filamentous green algae and mosses on the isoetid species. 4. The decline in light penetration was mainly caused by increased humic content following storm falls in 1981–84, but increased nutrient deposition may also have stimulated the growth of phytoplankton and filamentous green algae. The restricted macrophyte growth in the hypolimnion during summer can account for the change from oxygen supersaturation 40 years ago to anoxia today. The reduced light penetration has resulted in cooling of the hypolimnion, thereby increasing the stability and duration of thermal stratification. This increases the likelihood of anoxia in August–September. Profound changes in the plant community and in oxygen conditions have occurred, even though the decline of pH has been small and long-term changes in nutrient concentration have been difficult to detect.     

Plant compositional change over time increases with rainfall in Serengeti grasslands

Previous work from the Plains of Serengeti National Park (SNP) suggested that plant species composition (i.e. the composite measure of species' identities and abundances) is unchanged on the temporal scale of decades ( Belsky 1985 ), raising the possibility that African grazing ecosystems may be resistant to climate change. In this study, grassland plant composition was measured three times between 2000 and 2007 at eight permanent sites spanning the SNP environmental gradient. Confirming previous work, plots in the Serengeti Plains were relatively stable with respect to plant composition through time. In contrast, sites in all other regions of the ecosystem showed greater change in plant species composition during the study. Three factors, annual rainfall, dry season rainfall, and fire frequency, were linearly correlated (all r>0.73) with the amount of composition change at the sites. A path model, which accounted for the strong correlation between annual and dry season rainfall and for the known effect of annual rainfall on fire frequency, was used to elucidate which factors were associated with composition change and which were spuriously correlated. The path model demonstrated that change in plant composition was positively related to annual rainfall, but not dry season rainfall or fire frequency. However, dry season rainfall was positively associated with changes in plant species identity, one component of compositional change, across sites over time. Because climate models predict both increased wet season and decreased dry season rainfall in East Africa, these findings raise uncertainty about how these grasslands will respond to future changes. This study and others ( Belsky 1985 ) suggests that plant assemblages adapted to low rainfall in Serengeti may exhibit compositionally stability, while the same may not be true in regions of higher average rainfall and larger species pools.     

Influence of shifts over an 80-year period in forest composition on soil properties

Background and aims

Forest composition in North America has undergone important changes since the European settlement. The effects of such alterations on soil properties remain largely unknown. This study aims to understand the long-term effects of shifts in forest composition on soil properties.

Methods

Using data from 130 plots measured over an eighty-year period, the relationships between stand composition (both current and past), parent material and current soil chemical properties were studied with redundancy analyses.

Results

Results indicated that the parent material remained the dominant factor explaining soil properties, followed by current tree species composition. No legacy effect of past forest composition was found, but shifts in forest composition explained part of the current soil properties. Specifically, an increase in balsam fir was related to higher C/N ratio in the O-horizon, while an increase in maple species was related to higher net nitrification in both the O and B-horizons, and higher extractable P in the B-horizon.

Conclusion

Our results suggest that increasing the maple component at the expense of conifers over several decades may enhance nutrient availability in the O-horizon.

     

Evaluation of the eight-year period of compulsory measles vaccination in the Czech Socialist Republic (CSR)

The object of the study is the evaluation of a more than 8-year period of compulsory vaccination against measles in the CSR. So far, a total of 1,850,000 children have been vaccinated. A pronounced decrease has been achieved in morbidity while mortality and lethality reached zero values as early as in 1973. Changes occur in the epidemiological characteristic of measles manifested primarily by the shift of the age distribution of notified cases into older age groups, by continuous prolongation of interepidemic intervals and by gradual disappearances of typical seasonal incidence. Regular immunological surveys have become the most efficient tools in epidemiological surveillance of this infection and in monitoring the vaccination programme. The results of immunological surveys indeed led to the introduction in 1975 of so-called second vaccination compulsory for children starting the first year of school attendance. Up to the present, a total of 24,000 cases of measles have been recorded in children vaccinated earlier, i.e., 1.5% of the total of vaccinated children. It can be expected that measles as a mass disease will be eliminated from the territory of the CSR in the next few years.     

Above-ground biomass changes over an 11-year period in an Amazon monodominant forest and two other lowland forests

Tropical rain forest dominated by Peltogyne gracilipes (Fabaceae) occurs on Maracá Island, Roraima, Brazil, on a range of soil types. Three forest types were stratified for sampling, according to the occurrence of Peltogyne trees: (1) Peltogyne-rich forest (PRF), (2) Peltogyne-poor forest (PPF), and (3) forest without Peltogyne (FWP). Biomass increment and change in total stand biomass were calculated from mortality, recruitment, and growth data for trees in the three forest types. Data were derived from permanent plots established in 1991, where all trees (≥10 cm diameter at breast height), including palms and vines (lianas), were tagged and measured in three plots, each of 0.25 ha, in each of the three forest types. Field surveys were carried out in October 1991 and March 2003. Over a period of 11 years, the above-ground biomass in all forest types declined slightly (<5%), associated with the death of large trees, especially in the monodominant forests (PRF and PPF). Within the study period, the forest on Maracá experienced two heavy droughts, related to El Niño events (1997–1998 and 2002–2003) and most mortality and loss of biomass probably occurred during these events. Therefore, as the Maracá forests appear not be increasing in above-ground biomass overall, they may not be acting as a sink for atmospheric CO₂. The trees of the five most abundant species (Ecclinusa, Lecythis, Licania, Peltogyne, and Pradosia) accounted for about 55% of the total biomass in both FWP and PPF and for 74% in PRF. Peltogyne gracilipes had a stable, regenerating population in PRF, and is clearly a persistent dominant in a monodominant forest.     

Alien plant species coexist over time with native ones in Chilean Mediterranean grasslands

Aims Alien species are commonly considered as harmful weeds capable of decreasing native biodiversity and threatening ecosystems. Despite this assumption, little is known about the long-term patterns of the native–alien relationships associated with human disturbed managed landscapes. This study aims to elucidate the community dynamics associated with a successional gradient in Chilean Mediterranean grasslands, considering both native and alien species.Methods Species richness (natives and aliens separately) and life-form (annuals and perennials) were recorded in four Chilean post-agricultural grazed grasslands each covering a broad successional gradient (from 1 to 40 years since crop abandonment). A detrended correspondence analysis (DCA), mixed model effects analyses and correlation tests were conducted to assess how this temporal gradient influenced natives and aliens through community dynamics.Important findings Our results show different life-form patterns between natives and aliens over time. Aliens were mainly represented by annuals (especially ruderals and weeds), which were established at the beginning of succession. Annual aliens also predominated at mid-successional stages, but in old grasslands native species were slightly more representative than alien ones within the community. In the late successional states, positive or no correlations at all between alien and native species richness suggested the absence of competition between both species groups, as a result of different strategies in occupation of the space. Community dynamics over time constitute a net gain in biodiversity, increasing natives and maintaining a general alien pool, allowing the coexistence of both. Biotic interactions including facilitation and/or tolerance processes might be occurring in Chilean post-agricultural grasslands, a fact that contradicts the accepted idea of the alien species as contenders.     

Stereotaxic cytology of brain tumors. Review of an eight-year experience

The cytologic diagnosis of 312 stereotaxic samplings performed on 292 patients suspected of having a brain tumor over an eight-year period was reviewed. At different depths of the stereotaxic track, biopsy specimens were secured for cytologic and histologic observations. Smears for cytology were stained both by the May-Grünwald-Giemsa and the Papanicolaou methods since each of them disclosed information complementary to the other. Cytology and histology were in good agreement in 87.5% of the cases. Analysis of the data revealed a cytologic sensitivity of 88.8% and a specificity of 81.9%. The main difficulty encountered was differentiating between nonspecific glial hyperplasia and low-grade astrocytoma. To a lesser degree, differentiating metastases from glioblastoma sometimes was a problem. Stress is laid on the reliability of this type of cytology, its great help when sectioning of unfit specimens makes histologic evaluation hazardous, and its obvious importance when craniotomy is not desirable but a precise pathologic diagnosis is necessary for therapeutic decision. The stereotaxic procedure is briefly reviewed, and the main cytologic findings for the principal lesions encountered are illustrated and discussed.     

Changes over three decades in the floristic composition of nutrient-poor grasslands in the Swiss Alps

To investigate recent changes in the floristic composition and nature conservation value of nutrient-poor, semi-natural grasslands of the Swiss Alps, we resurveyed 151 phytosociological relevés in four regions, originally recorded between 1975 and 1985. In the original surveys, the mean number of plant species per plot (25–100 m²) ranged from 47.1 to 58.1 according to region. The flora included a total of 18 species that are protected in Switzerland and a high proportion of habitat specialists of nutrient-poor grasslands (NPG-species). In the second survey, conducted between 2002 and 2004, both mean species number per plot (−3.2 to +11.4) and species evenness (−0.05 to +0.07) were higher in most regions. However, the data revealed clear shifts in community composition, with a higher proportion of nutrient-demanding species (mean nutrient indicator value increased by +0.07 to +0.24 units) and a lower proportion per plot of NPG-species (−3.6 to −11.6%). These changes were greatest in pastures, and in meadows converted to sheep pastures, while the NPG-species were maintained in unfertilized meadows that were managed as ecological compensation areas. To prevent continuing decline in the conservation value of these grasslands, it is important to support low-intensity management, especially mowing, and to prevent further eutrophication.     

Selection against demographic stochasticity in age-structured populations

It has been shown that differences in fecundity variance can influence the probability of invasion of a genotype in a population; i.e., a genotype with lower variance in offspring number can be favored in finite populations even if it has a somewhat lower mean fitness than a competitor. In this article, Gillespie's results are extended to population genetic systems with explicit age structure, where the demographic variance (variance in growth rate) calculated in the work of Engen and colleagues is used as a generalization of "variance in offspring number" to predict the interaction between deterministic and random forces driving change in allele frequency. By calculating the variance from the life-history parameters, it is shown that selection against variance in the growth rate will favor a genotypes with lower stochasticity in age-specific survival and fertility rates. A diffusion approximation for selection and drift in a population with two genotypes with different life-history matrices (and therefore different mean growth rates and demographic variances) is derived and shown to be consistent with individual-based simulations. It is also argued that for finite populations, perturbation analyses of both the mean and the variance in growth rate may be necessary to determine the sensitivity of fitness to changes in the life-history parameters.     

杨树林全生长期LAI遥感估算模型适用性

基于时间序列的植被叶面积指数(LAI)估算方法一直是遥感领域研究的热点,对植被全生长期LAI进行估算以跟踪其生长情况具有重要的实用意义。以此为出发点,以滁州地区杨树林为研究对象,获取多时相环境卫星CCD(简称HJ-CDD)遥感影像,并利用LAI-2000同步测量杨树林叶面积指数(LAI)。使用归一化植被指数(NDVI)分别建立展叶期、花果期、叶面积稳定期和落叶始期的LAI估算模型,通过对比分析得到了全生长期LAI估算模型,并利用实测LAI对估算LAI进行了验证。最后进一步对该模型的适用性进行了验证,结果表明,此模型对于各个时期LAI的估算具有一定的适用性和有效性,可用于全生育期的遥感LAI生成,从而为LAI的动态变化监测提供了一种有效的研究思路和方法途径。     

Exotic shrub invasion in an undisturbed wetland has little community-level effect over a 15-year period

In this long-term study, we examined the invasion by the exotic shrub glossy buckthorn (Rhamnus frangula L.) and the response of co-occurring plants in a large, undisturbed wetland. We first sampled the vegetation in 1991 and repeated the sample 15 years later using the same, permanently located sample units (n = 165). Despite dramatic increases in the abundance of buckthorn, the invasion elicited little apparent response by the resident plant community. Species richness and cover in the herbaceous plant stratum had no apparent relationship with change in buckthorn cover. The number of shrub species other than buckthorn showed no relationship with change in buckthorn cover, but the cover of other shrubs decreased as buckthorn cover increased. Species composition changed independently of changes in buckthorn cover. These results show that dramatic increases in the abundance of an invasive species do not necessarily cause large changes in the native plant community and suggest disturbance history influences community response to invasion.     

Selection against immigrants in wild seabird populations

Immigration is a major demographic parameter shaping population dynamics and is an important driver of eco‐evolutionary patterns, but the fitness consequences for individuals following their settlement to a new population (immigrants) remain poorly tested in wild animal populations, particularly among long‐lived species. Here we show that immigrants have a lower fitness than residents in three wild seabird populations (wandering albatross Diomedea exulans, southern fulmar Fulmarus glacialoides, snow petrel Pagodroma nivea). Across all species and during a 32‐year period, immigrants made on average ?9 to 29% fewer breeding attempts, had 5–31% fewer fledglings, had 2–16% lower breeding success and produced 6–46% fewer recruits. Female immigration and male residency were also favored through differences in breeding performance. We provide evidence for selection against immigrants in wild populations of long‐lived species and our results are consistent with female‐biased dispersal in birds being driven by asymmetric limiting resources and the competitive ability of dispersers vs. non‐dispersers.     

Factors affecting changes in grey partridge population dynamics in a French arable farmland over an eleven-year period

The grey partridge Perdix perdix is of conservation concern owing to habitat heterogeneity losses and the negative impact of other environmental factors, e.g., pesticide use, predators, weather or shooting pressure, which are known to be associated with population decline. By an 11-year-period study in an intensively cultivated farmland located in the Paris basin, we aimed to relate the changes in grey partridge population dynamics with the changes in agriculture, monthly rainfall and shooting pressure. Summer drought occurred at the middle time of the study period. At the start of our study, a new cultivation, winter-wheat broadcast in maize-stubble fields, was introduced that probably improved the habitat. But in the next years, there was a loss in habitat diversity due to the disappearance of pastures dedicated to sheep rearing, removal of non-cropped areas and field boundaries and increase in the mean field size. Shooting was annually adjusted to what the owner believed to be a wise harvest. In post-breeding coveys, both percentages of hens with young among total hens and young-to-successful hens ratios first increased and then decreased. The mean brood size was rather weak during the dryness incident. The number of pairs in a more heterogeneous sector was always greater than in a less one. In both sectors, spring abundance first increased and then decreased. In the second half of the study period, the shooting quotas were reduced, especially when the mean brood size fell down. Low hatching rates of clutches and low chick survival rates explain the population decline, as the results are convincing. To stop the population decline in intensive arable farmland, good breeding success is needed. This can be provided by favourable habitats for hens to nest and for chicks to feed.     

On Predator Selection against Abnormalities of Movement A Test of an Hypothesis1

If debilitated prey items can be caught more efficiently than healthy ones, there is a selective advantage for predators to detect any weakness in their prey. This study investigates whether three-spined sticklebacks (Gastcrosteus aculeatus L.) accustomed to feeding on one or the other of two types of waterfleas differing in their swimming pattern capture the unfamiliar type when given a choice. Such sequential oddity selection might serve as a mechanism for the detection of sick prey.     

The Distribution of Enzyme and Inversion Polymorphism over the Genome of Drosophila: Evidence against Balancing Selection

In species of repleta group of Drosophila about 70% of the electrophoretic variability is absorbed by the same chromosome which absorbs about 70% of the cytological variability of the group. However, this does not imply that inversions are actively involved in the maintenance of protein variation. A comparison of cytological and electrophoretic variation of homologous chromosomes points out that the amount of cytological polymorphism varies greatly over species of Drosophila while electrophoretic variation does not. This suggests that allelozymes do not constitute part of the coadapted complexes of genes characterizing the inversions. Rather, the amount of electropheptide molecule and is largely independent of factors such as background genotype and differences in the environment.