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Throughout eastern North America, stands of northern red oak (Quercus rubra L.) are undergoing successional replacement by shade-tolerant competitors. In the Great Lakes-St. Lawrence (GLSL) forest region, Q. rubra approaches the northern limit of its distribution, and ecosystem-specific silvicultural directives are needed to promote regeneration. We used an inductive, ordination-based approach to explore patterns in understorey plant community composition and microenvironment under different partial harvest treatments applied in a GLSL hardwood stand, and related these to characteristics of natural seedlings of Q. rubra and its competitors Acer rubrum and Acer saccharum.Two years after harvest, we established 2 m × 2 m plots in a stratified random design under 70% (n = 20) and 50% (n = 19) crown closure uniform shelterwood, group selection (n = 15), and uncut upper slope (n = 10) and lower slope (n = 10) areas. Percent cover of understorey vascular plant species, and a suite of microclimatic and edaphic variables were measured in each plot. Density, mean diameter and mean height of seedlings in the understorey (height <1 m) were determined in each plot for Q. rubra, A. rubrum and A. saccharum.Correspondence analysis (CA) ordination extracted two major axes explaining 21.6% of the total inertia in the species cover by plot matrix. Axis one separated uncut plots from the 50% shelterwood along a gradient of canopy cover associated with partial harvest treatments. Plot scores on axis one (13.2%) reflected a shift in dominance of the understorey from shade-tolerant Acer spp. to shade-intolerant colonizers, Rubus idaeus and Carex spp. Plot scores on axis one were directly (p < 0.05) associated with total understorey plant cover, litter depth, soil temperature and pH, but not with measures of plant diversity. Axis two (8.4%) separated plots from upper slope and lower slope areas, and plot scores were inversely associated (p < 0.05) with soil pH, phosphorus and nitrogen levels. Along axis two there was a shift in dominance from competitive (e.g. A. saccharum) to stress-tolerant (e.g. A. rubrum) species as soil fertility declined. Stepwise linear regression indicated seedling diameter in Q. rubra, A. rubrum and A. saccharum was inversely related to canopy cover. This suggests all three species benefited from partial harvest, although the relationship was strongest in Q. rubra. Patterns in understorey composition, microenvironment and seedling characteristics provide the basis to identify the main competitors of Q. rubra seedlings and adjust regeneration efforts along gradients of canopy closure and soil fertility under partial harvest systems within the GLSL forest region. 相似文献
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John Connell 《Asia Pacific viewpoint》2006,47(3):342-350
Abstract: Effective global competitiveness is rare in the Pacific islands, yet FIJI Water has been a major success story since 1997, exporting bottled water to the USA and elsewhere. A bland commodity has been linked to an ‘exotic’ place, and sold to elite consumers, as a form of cultural capital. The company website and newspaper extol the virtues of a ‘pristine’ product, produced in a natural context, in an environmentally sensitive manner. Marketing these themes and product placement have enabled success in a highly competitive market. Place has been used as a means of marketing perceived taste, distinctiveness and quality. 相似文献
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Abstract – This study assessed the size‐related patterns of dietary resource use in terapontid assemblages from two north Australian wet‐dry tropical river systems exhibiting contrasting long‐term flow regimes. Substantially higher size‐related dietary divergence in the form of additional trophic guilds and lower levels of dietary overlap were evident among terapontids from the comparatively stable Daly River system, particularly during the dry season. Relatively restricted expression of size‐related dietary shifts in conjunction with higher levels of dietary overlap and no significant seasonal effects on dietary overlap were features of assemblage interaction in the highly variable Burdekin River. Results highlight size‐related dietary shifts as a complex aspect of terapontid trophic habits, and one that can exhibit considerable spatial dynamism. 相似文献
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林岩;丁晓宇;吕航;卢兴顺;李佳;赵子闻;武琳慧 《水生态学杂志》2023,44(3):102
In this study, we explored the phytoplankton community structure and ecological niche characteristics of Ulansuhai Lake during the ice-on period and analyzed interspecific associations of phytoplankton based on theoretical conceptions of ecological niche breadth and overlap. Our objective was to provide basic data to support nutrient evaluation and pollution treatment of the lake. Based on the distribution of pollution sources, hydrology and environmental characteristics of Ulansuhai Lake, 16 representative sites were selected, including the inlet (N1-N6), open area (N7-N14) and outlet (N15, N16) of the lake for sampling phytoplankton and water in January (winter) of 2018 and 2019. The Improved Levins formula and Petraitis Index were used to determine niche breadth and niche overlap of dominant phytoplankton species. A total of 99 phytoplankton species from 7 phyla were identified during the two investigations, with 57 species from 7 phyla in 2018 and 63 species from 7 phyla in 2019. Among them, six species from two phyla in 2018 and 8 species from 6 phyla in 2019 were dominant during the ice-on period, with the absolute dominance by Pseudoanabaena sp. in 2018 and the absolute dominance by Chroomonas sp. and Trachelomonas volvocina in 2019. The niche width of the dominant species in the ice-on period was 0.0711-0.5971 in 2018, and Chlamydomonas globosa had the largest niche width, followed by Stylosphaeridium stipitatum and Chlamydomonas sp. In 2019, the niche width of the dominant species was in the range of 0.1265-0.5455, and Stylosphaeridium stipitatum had the largest niche width, followed by Komma caudata and Chroomonas sp.. In 2018 and 2019, the niche overlap values of the dominant species were 0.0078-0.7967 and 0.0448-0.9248, respectively, and the niche overlap values were generally small. The overlap degree of Chlamydomonas sp. and Chlamydomonas globosa was highest in 2018, and the overlap degree of Komma caudata and Chroomonas sp. was highest in 2019. The overlap of ecological niches and the rate of ecological response indicates that phytoplankton community showed an overall developing trend in 2018 and a declining trend in 2019. The analysis of the variance ratio method showed that, overall, the dominant species were positively correlated. The chi-square test indicated that the association between dominant species was not significant, and most algae species were negatively correlated, with a few species displaying positive correlations. 相似文献
6.
Environmental divergence along hierarchically structured longitudinal gradients may constitute barriers to gene flow in river networks for headwater specialised species. While known, this phenomenon has not been well studied, especially with regard to degree of headwater specialisation. We examined six headwater species that differ in habitat specialisation to assess whether patterns of differentiation vary according to geographic or environmental distance. We also identified regional environmental or anthropogenically induced fragmentation effects by comparing within‐drainage patterns of genetic distance across replicate watersheds. We used a comparative modelling framework to determine whether isolation by distance or isolation by resistance of large river habitats was a better predictor of genetic distance across species. The influence of reservoir presence and regional network characteristics that may influence the hydrology and size of large river habitats were also assessed. Resistance effects from large rivers were closely related to headwater specialisation, with increased specialisation leading to increased resistance and loss of drainagewide population connectivity. These results affirm that dendritic networks naturally fragment headwater specialised species. Further isolation from anthropogenic fragmentation was detected in two of the six drainages, indicating interactions with system‐specific conditions. Landscape variables related to the hydrology of large rivers also affected genetic distance in predicted ways, supporting the importance of large rivers in genetically structuring headwater species in drainage networks. 相似文献
7.
《Scandinavian Journal of Forest Research》2012,27(1-4):521-535
The common rhizospheric fungus Cylindrocarpon destructans was investigated in relation to its role in root death of Pinus sylvestris in Nordic nurseries and plantations. Laboratory methods were developed for studying similar root problems as well as the early effects of phytotoxicity and fungal infection. Seedlings grown under standardized optimal conditions were exposed to controlled stress (known to occur in nurseries), with or without C. destructans in the rhizosphere. Low light conditions, anaerobic root environment, and fungicide treatment were each found to predispose pine seedlings to invasion by the pathogen. The pathogen was very sensitive to competition as well as antagonism on the root, and fungicide‐induced inhibition of antagonists such as Trichoderma spp. also increased the severity of attack by the pathogen. To compete successfully, the pathogen would have to invade and dominate weakened roots prior to the arrival of saprophytes. Toxic metabolites produced by the pathogen weakened or killed nearby root tissues, and pathogen metabolites seemed to prevent saprophytes from taking hold in the infected roots. Such heavily infected, dead roots may act as inoculum sources allowing the pathogen to invade adjacent living roots, even healthy ones. Dead roots left in nursery soil after earlier harvests may act as reservoirs of inoculum for long periods and pose a threat to new plants. 相似文献
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松材线虫染病黑松上钻蛀性昆虫生态位的研究 总被引：2，自引：0，他引：2
2006年8月和10月,在浙江省舟山市和安徽省滁州市的松材线虫病典型发生区调查了黑松上的钻蛀性害虫的种类,分析了衰弱木上优势虫种的生态位宽度、生态位相似性和生态位重叠值。结果表明：在感染松材线虫病的黑松上共发现7种昆虫,其中钻蛀类害虫5种,天敌2种。在两地生活于松树主干上的昆虫种类不尽相同,而且具有各自不同的生态位宽度,存在不同程度的生态位重叠,对空间和营养资源的利用有不同比例的相似性。依据其各自生物学特性和生活习性的不同达到竞争的平衡和共存。 相似文献
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