Fire season and intensity affect shrub recruitment in temperate sclerophyllous woodlands

The season in which a fire occurs may regulate plant seedling recruitment because of: (1) the interaction of season and intensity of fire and the temperature requirements for seed release, germination and growth; (2) post-fire rainfall and temperature patterns affecting germination; (3) the interaction of post-fire germination conditions and competition from surrounding vegetation; and (4) the interaction of post-fire germination conditions and seed predators and/or seedling herbivores. This study examined the effects of different fire intensities and fire seasons on the emergence and survival of shrubs representing a range of fire response syndromes from a summer rainfall cool climate region. Replicated experimental burns were conducted in two seasons (spring and autumn) in 2 consecutive years and fuel loads were increased to examine the effects of fire intensity (low intensity and moderate intensity). Post-fire watering treatments partitioned the effects of seasonal temperature from soil moisture. Higher intensity fires resulted in enhanced seedling emergence for hard-seeded species but rarely influenced survival. Spring fires enhanced seedling emergence across all functional groups. Reduced autumn recruitment was related to seasonal temperature inhibiting germination rather than a lack of soil moisture or competition. In Mediterranean-type climate regions, seedling emergence has been related to post-fire rainfall and exposure of seeds to seed predators. We think a similar model may operate in temperate summer rainfall regions where cold-induced dormancy over winter exposes seeds to predators for a longer time and subsequently results in recruitment failure. Our results support the theory that the effect of fire season is more predictable where there are strong seasonal patterns in climate. In this study seasonal temperature rather than rainfall appears to be more influential.     

Environmental determinism of year-to-year recruitment variability of European eel Anguilla anguilla in a small coastal catchment, the Frémur River, north-west France

The influence of environmental factors (mainly the river flow) on the year-to-year variability of European eel Anguilla anguilla fluvial recruitment in a small coastal catchment, the Frémur River (north-west France) was examined. A comprehensive survey of catches from fixed traps at two weirs located at 4·5 km (Pont es Omnes Dam) and 6·0 km (Bois Joli Dam) above the river mouth was carried out between 1997 and 2004. Young pigmented elvers (mean ± s.d. total length, 133·7 ± 29·6 mm) were recruited in eel-passes from February to October, but the main runs followed a modal curve from April to September with a peak centred in May to June. Catches varied greatly between years, from 381 to 26 765 elvers. For each trap, a positive linear relationship between monthly mean river flow that preceded the maximal intensity of captures and annual total catches was observed. These relationships explained 73·1% ( P < 0.01) and 89·0% ( P < 0.001) of the year-to-year variability of the recruitment observed in the Pont es Omnes and Bois Joli traps respectively. A significant increase in river flow at the beginning of the migration peak would thus trigger a greater proportion of A. anguilla settled in the estuary and in the downstream zone of the Fremur River to begin their freshwater colonization. The physicochemical roles of changes in river discharge in stimulating upstream migration are discussed. It is concluded that fluvial recruitment in the Fremur River is mainly determined by environmental factors.     

沈阳细河水中多环芳烃的分布、来源及生态风险评价

通过测定不同季节细河水中多环芳烃(PAHs)的含量,研究了细河水中PAHs的分布,探讨了PAHs的来源,评价了其生态风险。细河水中6月(夏季)16种PAHs的含量为0.214～0.857μg·L-1,平均为0.562μg·L-1;9月(秋季)水中PAHs含量为0.195～0.633μg·L-1,平均0.380μg·L-1;11月(冬季)水中PAHs含量为0.122～0.486μg.L-1,平均含量为0.236μg·L-1。苯并(a)芘含量明显高于国家地表水环境质量标准(GB3838-2002);对细河水中PAHs污染来源分析发现,6月和9月PAHs的主要来源为石油污染和石油及其精炼产品的燃烧;通过商值法对细河的初步风险评价表明,细河水中苯并(a)芘存在较大的生态风险,应引起关注。     

Historical distribution patterns of trigonioidids (non-marine Cretaceous bivalves) in Asia and their palaeogeographic significance

The non-marine trigonioidid bivalves show five phases of radiation in the Cretaceous of Pal-Asia: pre-Aptian (?Valanginian/Hauterivian–Barremian), Aptian, Albian, Cenomanian and Turonian–Maastrichtian. Their distribution patterns show two distinct palaeo-river systems feeding trigonioidids. Before the Cenomanian, the river system occupied the southwestern–southern–southeastern Pal-Asian continental margin areas. During the Turonian–Maastrichtian, it extended along the line of southcentral China−eastern China−northeastern China−northern China and Mongolia−northwestern China–eastern Fergana Basin of Kyrgyzstan−western Tajikistan Basin of Tajikistan–Tashkent area of Kazakhstan−central Kyzylkum of northern Uzbekistan–Aral Sea area of Kazakhstan. Furthermore, the general trigonioidid distribution pattern demonstrates that Japan was probably attached to part of eastern China and/or Korea during the ?Valanginian/Hauterivian–Cenomanian stages.     

Ecosystems patterns and dynamics in Haihe river basin

Research on ecosystems patterns and dynamics is critical for understanding the regional problems of resources and environment. In this study, based on the technology of RS and GIS, the composition, patterns and dynamics of the ecosystems in Haihe river basin during 1990–2005 were analyzed using landscape indices including the area of average patches, aggregation index and Shannon–Weaver diversity index. According to the development situation of economy and society in Haihe river basin, some driving factors for dynamics of ecosystems patterns were concluded based on correlation analysis. Results showed that the ecosystems patterns in Haihe river basin changed greatly from 1990 to 2005. The area of urban and grassland increased, but farmland, forest and wetland decreased. As for landscape indices, the area of average patches, value of aggregation index, clump index and diversity index all increased, indicating the trend of evenness for the whole ecosystems. Growth of population, economy growth together with urbanization and policy were the main driving factors for dynamics of ecosystem pattern in this basin.     

Use of invertebrate traits for the biomonitoring of European large rivers: the effects of sampling effort on genus richness and functional diversity

1. Studies on biodiversity and ecosystem function require considering metrics for accurately describing the functional diversity of communities. The number of taxa (richness) is commonly used to characterise biological diversity. The disadvantage of richness as a measure of biological diversity is that all taxa are taken into account on an equal basis regardless of their abundance, their biological characteristics or their function in the ecosystem. 2. To circumvent this problem, we applied a recently described measure of biological diversity that incorporates dissimilarities among taxa. Dissimilarities were defined from biological traits (e.g. life history, morphology, physiology and behaviour) of stream invertebrate taxa and the resulting biological diversity index was considered as a surrogate for functional diversity. 3. As sampling effort is known to affect the number of taxa collected within a reach, we investigated how change in functional diversity is affected by sampling effort. We used stream invertebrate community data from three large European rivers to model accumulation curves and to assess the number of samples required to estimate (i.e. closeness to the maximal value) functional diversity and genera richness. We further evaluated the precision of estimates (i.e. similarity of temporal or spatial replicates) of the total functional diversity. 4. As expected, richness estimates were strongly dependent on sampling effort, and 10 replicate samples were found to underestimate actual richness. Moreover, richness estimates showed much variation with season and location. In contrast, functional diversity had greater accuracy with less sampling effort and the precision of the estimates was higher than richness both across sampling occasions and sampling reaches. These results are further arguments towards conducting research on the design of a biomonitoring tool based on biological traits.     

Landscape scale effects of disturbance on riparian vegetation

1. Differing responses in riparian species richness and composition to disturbance have been reported as a possible explanation for the differences along and between rivers. This paper explores the role of physical disturbance in shaping landscape‐scale patterns of species distribution in riparian vegetation along a free‐flowing river in northern Sweden. 2. To test whether sensitivity to disturbance varies across large landscapes, we experimentally disturbed riparian vegetation along an entire, free‐flowing river by scouring the soil and the vegetation turf, cutting vegetation, applying waterborne plant litter, and after a period of recovery we measured vegetation responses. The experiment was repeated for two consecutive years. 3. We found no significant effect of disturbance on species composition, but all three forms of disturbance significantly reduced species richness. There was no downstream variation in community responses to disturbance but morphological groups of species responded differently to different kinds of disturbance. Graminoids were most resistant, suppressed only by litter burial. All forms of disturbance except cutting reduced the density of herbaceous species, and species density of trees + shrubs and dwarf shrubs was negatively affected by both scouring and cutting. We also evaluated the effects of disturbance in relation to varying levels of species richness. In nearly all cases, responses were significantly negatively correlated with control plot species richness, and relative responses indicated that species‐rich plots were less resistant to scouring and cutting. 4. Our results suggest that although all disturbance treatments had an effect on species richness, variation in sensitivity to disturbance is not the most important factor shaping landscape‐scale patterns of riparian plant species richness along rivers.     

Management options for river conservation planning: condition and conservation re-visited

1. Systematic conservation planning is a process widely used in terrestrial and marine environments. A principal goal is to establish a network of protected areas representing the full variety of species or ecosystems. We suggest considering three key attributes of a catchment when planning for aquatic conservation: irreplaceability, condition and vulnerability. 2. Based on observed and modelled distributions of 367 invertebrates in the Australian state of Victoria, conservation value was measured by calculating an irreplaceability coefficient for 1854 subcatchments. Irreplaceability indicates the likelihood of any subcatchment being needed to achieve conservation targets. We estimated it with a bootstrapped heuristic reserve design algorithm, which included upstream–downstream connectivity rules. The selection metric within the algorithm was total summed rarity, corrected for protected area. 3. Condition was estimated using a stressor gradient approach in which two classes of geographical information system Layers were summarised using principal components analysis. The first class was disturbance measures such as nutrient and sediment budgets, salinisation and weed cover. The second class was land use layers, including classes of forestry, agricultural and urban use. The main gradient, explaining 56% of the variation, could be characterised as agricultural disturbance. Seventy‐five per cent of the study area was classified as disturbed. 4. Our definition of vulnerability was the likelihood of a catchment being exposed to a land use that degrades its condition. This was estimated by comparing land capability and current land use. If land was capable of supporting a land use that would have a more degrading effect on a river than its current tenure, it was classified vulnerable (66% of the study area). 79% of catchments contained more then 50% vulnerable land. 5. When integrating the three measures, two major groups of catchments requiring urgent conservation measures were identified. Seven per cent of catchments were highly irreplaceable, highly vulnerable but in degraded condition. These catchments were flagged for restoration. While most highly irreplaceable catchments in good condition were already protected, 2.5% of catchments in this category are on vulnerable land. These are priority areas for assigning river reserves.     

Food web transfer of plastics to an apex riverine predator

As a rapidly accelerating expression of global change, plastics now occur extensively in freshwater ecosystems, yet there is barely any evidence of their transfer through food webs. Following previous observations that plastics occur widely in their prey, we used a field study of free‐living Eurasian dippers (Cinclus cinclus), to test the hypotheses that (1) plastics are transferred from prey to predators in rivers, (2) plastics contained in prey are transferred by adults to altricial offspring during provisioning and (3) plastic concentrations in faecal and regurgitated pellets from dippers increase with urbanization. Plastic occurred in 50% of regurgitates (n = 74) and 45% of faecal samples (n = 92) collected non‐invasively from adult and nestling dippers at 15 sites across South Wales (UK). Over 95% of particles were fibres, and concentrations in samples increased with urban land cover. Fourier transform infrared spectroscopy identified multiple polymers, including polyester, polypropylene, polyvinyl chloride and vinyl chloride copolymers. Although characterized by uncertainty, steady‐state models using energetic data along with plastic concentration in prey and excreta suggest that around 200 plastic particles are ingested daily by dippers, but also excreted at rates that suggest transitory throughput. As some of the first evidence revealing that plastic is now being transferred through freshwater food webs, and between adult passerines and their offspring, these data emphasize the need to appraise the potential ecotoxicological consequences of increasing plastic pollution.