首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
This study examined differences in stand structure, tree species richness, and tree species diversity in relation to population density in Kampong Thom Province, Cambodia. Tree data were obtained from a 1997 forest inventory involving 60 clusters (540 plots) systematically distributed over 30% of the provincial forest area. Spatially referenced population data were obtained from the 1998 national population census. The average number of trees per cluster was 356/ha, the average basal area, 23 m2/ha, the average stand volume, 217 m3/ha, and the average aboveground biomass, 273 Mg/ha for all trees of DBH 10 cm and larger. The average species richness per cluster was 37 species, while average species diversity was measured as 0.916 using Simpson’s index and 2.98 by Shannon’s index. Significant negative correlations were generally found between population density surrounding clusters and tree density, basal area, stand volume, aboveground biomass, and species richness and diversity for three examined diameter classes (DBH of 10–30, ≥30, and ≥10 cm). As the distance from clusters for calculating population density increased, the correlation levels increased up to 5 or 7 km, depending on the variables and diameter class, and then stayed relatively constant for stand structure variables and decreased for species richness and diversity. The results indicate that evidence of disturbance was more pronounced at higher population density up to around 5 to 7 km. We suggest that introduction of greater controls on human disturbance should be a high priority for resource management and conservation in Kampong Thom Province and, presumably, Cambodia as a whole.  相似文献   

2.
In riparian meadows, narrow zonation of the dominant vegetation frequently occurs along the elevational gradient from the stream edge to the floodplain terrace. We measured plant species composition and above- and belowground biomass in three riparian plant communities—a priori defined as wet, moist, and dry meadow—along short streamside topographic gradients in two montane meadows in northeast Oregon. The objectives were to: (1) compare above- and belowground biomass in the three meadow communities; (2) examine relations among plant species richness, biomass distribution, water table depth, and soil redox potential along the streamside elevational gradients. We installed wells and platinum electrodes along transects (perpendicular to the stream; n=5 per site) through the three plant communities, and monitored water table depth and soil redox potential (10 and 25 cm depth) from July 1997 to August 1999. Mean water table depth and soil redox potential differed significantly along the transects, and characterized a strong environmental gradient. Community differences in plant species composition were reflected in biomass distribution. Highest total biomass (live+dead) occurred in the sedge-dominated wet meadows (4,311±289 g/m2), intermediate biomass (2,236±221 g/m2) was seen in the moist meadow communities, dominated by grasses and sedges, and lowest biomass (1,403±113 g/m2) was observed in the more diverse dry meadows, dominated by grasses and forbs. In the wet and moist communities, belowground biomass (live+dead) comprised 68–81% of the totals. Rhizome-to-root ratios and distinctive vertical profiles of belowground biomass reflected characteristics of the dominant graminoid species within each community. Total biomass was positively correlated with mean water table depth, and negatively correlated with mean redox potential (10 cm and 25 cm depths; P <0.01) and species richness (P <0.05), indicating that the distribution of biomass coincided with the streamside edaphic gradient in these riparian meadows.Electronic Supplementary Material Supplementary material is available in the online version of this article at  相似文献   

3.
Secondary succession is an increasing phenomenon due to global changes in agriculture policies and practices. The empirical findings are biased towards the temperate zone. Abandonment of agriculture fields is less frequent in the subtropical and tropical zones where agriculture areas are, in general, expanding. But there are exceptions; a rapid rate of abandonment of agricultural fields have taken place in the arid trans-Himalayan region, due to today’s globalization of economy. We analysed agriculture fields that were abandoned between 1950 and 2003 in a large u-valley in central Nepal (3400 m a.s.l.). The potential forest vegetation is dominated by Pinus wallichina and shrubs of junipers and cotoneaster species. We tested the intermediate richness hypothesis in relation to vegetation cover, soil development and whether old-field succession is convergent or divergent with species data from 242 1 m2 plots in 5 age-classes. The main species compositional turnover expressed by Detrended Correspondence Analyses (DCA) correlated, as expected, with time after abandonment. Fields that were abandoned a long time ago are closer to forest at the periphery of the agricultural landscape. Moisture of the soil significantly increased with age of abandonment, but total vegetation cover and pH were negatively related to age. Beta diversity expressed in DCA SD-units showed an increasing trend with age of abandonment, supporting the divergence pattern in old-field succession. The reason why the succession is not converging may be due to browsing by domestic animals that prevent a closed canopy of pines and juniper to develop. There was a significant hump-shaped pattern in species richness along the temporal gradient, which agrees with the intermediate species-richness hypothesis. There was a rapid increase in species richness in plots close to the villages that were used for haymaking which increased the seed input significantly.  相似文献   

4.
5.
Jensen  Kai  Meyer  Claudia 《Plant Ecology》2001,155(2):169-181
Theeffects of light competition and litter on seedling recruitment and theperformance of established individuals were examined in Violapalustris. This polycarpic perennial plant was a common component ofspecies-rich fen meadows in northwestern Germany until the middle of thiscentury, but today is considered to be regionally endangered. From summer 1996until summer 1998 a bi-factorial field experiment combining three standing croptreatments (mowing, thinning, control) with two litter layer treatments (litterremoval, no litter removal) was carried out in an abandoned fen meadow toinvestigate the effects of these factors both on V.palustris and on aboveground species composition and diversity.MANOVAs (multivariate analysis of variance) revealed significant treatmenteffects for the performance of V. palustris related toexperimental manipulation. Mowing increased vital attributes including thenumber of rosette leaves, the percentage of individuals with chasmogamous andcleistogamous flowers and the number of rhizomes. In contrast, the length of theleafstalk, mean leaf area and the length of rhizomes were negatively associatedwith mowing. Litter removal significantly increased the number of V.palustris seedlings. The removal of the litter layer already resultedin an increase in aboveground species richness in the first year of theexperiment. After three years of experimental manipulation, both abovegroundspecies richness and diversity were positively associated with mowing.Redundancy Analysis showed that typical wet meadow species (Cardaminepratensis, Lychnis flos-cuculi, Lotuspedunculatus) and species of mesotrophic fens (Violapalustris, Agrostis canina, Potentillapalustris) were positively influenced by mowing. It can be concludedthat V. palustris recruitment and growth is promoted by aregular disturbance regime on fen meadows. The conservation of many typicalspecies of wet meadows and fens in northwestern Germany depends on moderategrazing or cutting. These management types prevent successional changes whichlead to an increase in standing crop and the development of a litter layer, bothof which can cause local extinction.  相似文献   

6.
7.
This study aimed to assess the effects of accidental burning on plant cover and habitat conditions in abandoned Molinion caeruleae meadows. Field studies were conducted in Kraków (Southern Poland) in the years 2017–2019 in two line transects, each with 10 permanent plots established in permanent study plots placed in accidentally burned and unburned patches. In the burned patch, the number of species, as well as Shannon-Wiener, Pielou and Simpson indicators achieved lower values. Moreover, the cover of numerous taxa affiliated with Molinion caeruleae changed remarkably, while taxa representing the alliances Calthion and Filipendulion disappeared. The considerable dominance of hemicryptophytes was observed in burned site, while in unburned place hemicryptophytes and geophytes were represented most abundantly. In the burned patch, anemochorous and autochorous species as well as small-seeded taxa dominated, while in the unburned patch autochorous species and medium-seeded taxa prevailed. The values of Ellenberg indicators in the burned patch achieved greater (light, soil reaction), lower (nitrogen, humidity) or similar (temperature, continentality) values to the unburned patch. The majority of soil properties in the burned and unburned patches were similar with the exception of the significantly greater content of potassium and lower content of magnesium in exchangeable form noticed in the burned patch. The performed investigations showed that, although the accidental fire activity inhibited the secondary succession in Molinion caeruleae meadows, burning cannot replace traditional mowing due to the reduction of species richness and disappearance of characteristic taxa.  相似文献   

8.
Question: Can the biodiversity of fens in Europe and North America be maintained through the use of grazing (especially cattle grazing), fire, and/or cutting? Location: European and North American fens. Methods: This paper is a review of the literature on the effects of grazing, fire and cutting on fens, to explore the relationship between management and biodiversity in fens. Results: A reduction of cattle grazing, mowing and burning in fens has led to a reduction in biodiversity in fens. The vegetation of abandoned fens shifts to trees and shrubs after 10–15 years, which shade the smaller and rarer species of these wetlands. While careful use of fire is used to manage fens in North America, it is not widely used in European fens, perhaps because the peat of drained fens may catch fire. Cattle grazing cannot be considered a natural disturbance in North America, since cattle did not evolve on that continent. In Europe, cattle do not generally graze in unaltered fens, but they do use slightly drained fen meadows. Conclusions: Three approaches have been used to control the dominance of tall woody and herbaceous species in abandoned fens, including the re‐introduction of cattle, mowing, and burning. Overgrazing results in a permanent reduction in biodiversity, therefore cattle re‐introduction must be approached cautiously. In Europe, but not in North America, mowing has been an important management tool, and mowing has been successful in maintaining species richness, particularly in fens that have been mowed annually for centuries. Fire has been the most common and successful management tool in North America although it is not effective in removing shrubs that have become large. Because the problems and solutions are similar, the literature of both European and North American fen management can be analyzed to better assess the management of fens on both continents. Many management questions require further study and these are listed in the paper.  相似文献   

9.
Abstract. We compared the plant species composition, productivity and canopy structure of seven mown sites to a chronosequence of 20 abandoned calcareous fens in northeastern Switzerland. Cessation of mowing led to an 18% decline in overall plant species richness and the diversity of most functional groups. Abandonment did not lead to marked increases of above‐ground productivity, but rather selectively favoured certain functional groups. On abandoned fens biomass of grasses increased nearly threefold, at the expense of biomass of Cyperaceae and Juncaceae, which declined by 30% compared to mown fens, while forb biomass remained unaffected. Litter mass increased more than 15‐fold in fallows, while canopy height increased by 50%. The foliage in abandoned fens was oriented more horizontally and had a lower overall cover. However, these successional changes were never dependent upon the age of the fallow. Furthermore, nearly all traits differed significantly on regional and local spatial scales, suggesting that floristic and (meso‐)climatic differences obscure or override successional trajectories in these species‐rich wetlands.  相似文献   

10.
Little is known about the amount of fungal biomass in the phyllosphere of bryophytes compared to higher plants. In this study, fungal biomass associated with the phyllosphere of three bryophytes (Hylocomium splendens, Pleurozium schreberi, Polytrichum commune) and three vascular plants (Avenella flexuosa, Gymnocarpium dryopteris, Vaccinium myrtillus) was investigated using ergosterol content as a proxy for fungal biomass. Phyllosphere fungi accounted for 0.2-4.0 % of the dry mass of moss gametophytes, representing the first estimation of fungal biomass associated with bryophytes. Significantly more fungal biomass was associated with the phyllosphere of bryophytes than co-occurring vascular plants. The ergosterol present in moss gametophytic tissues differed significantly between species, while the ergosterol present in vascular plant leaf tissues did not. The photosynthetic tissues of mosses had less associated fungal biomass than their senescent tissues, and the magnitude of this difference varied in a species-specific manner. The fungal biomass associated with the vascular plants studied varied significantly between localities, while that of mosses did not. The observed differences in phyllosphere community biomass suggest their size could be affected by host anatomical and physiological attributes, including micro-niche availability and chemical host defenses, in addition to abiotic factors like moisture and nutrient availability.  相似文献   

11.
12.
We examined effects of seasonality of climate and dominant life form (evergreen/deciduous, broad-leaf/coniferous) together with energy condition on species diversity, forest structure, forest dynamics, and productivity of forest ecosystems by comparing the patterns of changes in these ecosystem attributes along altitudinal gradients in tropical regions without seasonality and along a latitudinal gradient from tropical to temperate regions in humid East Asia. We used warmth index (temperature sum during growing season, WI) as an index of energy condition common to both altitudinal and latitudinal gradients. There were apparent differences in patterns of changes in the ecosystem attributes in relation to WI among four forest formations that were classified according to dominant life form and climatic zone (tropical/temperate). Many of the ecosystem attributes—Fishers alpha of species-diversity indices, maximum tree height and stem density, productivity [increment rate of aboveground biomass (AGB)], and population and biomass turnover rates—changed sharply with WI in tropical and temperate evergreen broad-leaved forests, but did not change linearly or changed only loosely with WI in temperate deciduous broad-leaved and evergreen coniferous forests. Values of these ecosystem attributes in temperate deciduous broad-leaved and evergreen coniferous forests were higher (stem density was lower) than those in tropical and temperate evergreen broad-leaved forests under colder conditions (WI below 100°C). Present results indicate that seasonality of climate and resultant change in dominant life form work to buffer the effects of energy reduction on ecosystem attributes along latitudinal gradients.  相似文献   

13.
【目的】雅鲁藏布江是青藏高原最重要的河流,研究雅鲁藏布江的地上生物量和物种多样性对了解该区域的草地资源和生态保护具有重要意义。【方法】文章根据海拔梯度对雅鲁藏布江上游高寒草甸植被特征进行调查,研究不同海拔梯度下地上生物量和物种多样性的分布差异、地上生物量与物种多样性之间的关系,以及相关环境因子对地上生物量和物种多样性的影响。【结果】(1)海拔与地上生物量无显著关系;(2)海拔与多样性指数呈显著负相关关系,随海拔升高Shannon-Weiner指数、Patrick指数表现为下降趋势;(3)地上生物量与多样性之间表现为负相关关系,Shannon-Weiner指数对地上生物量的解释达到70%(P<0.01);(4)物种多样性与温度和降水呈显著正相关关系(P<0.05),物种多样性与海拔呈负相关关系(P<0.05),地上生物量与海拔、温度和降水无显著关系(P>0.05)。【结论】该研究结果有助于为雅鲁藏布江上游流域草地资源的合理利用和物种多样性保护提供依据。  相似文献   

14.
To study the impact of disturbance by mowing on clonal variation, we compared the genetic structure of Ranunculus ficaria (Ranunculaceae) in meadows and forests located in southeast Germany. We applied random amplified polymorphic DNA (RAPD) analysis to investigate the clonal and genetic diversity and analysed a total of 117 samples from three study plots in each habitat type. Polymerase chain reaction with six primers resulted in 57 fragments. Clonal diversity differed clearly between the two analysed habitat types and was significantly higher in the study plots from meadows than in those from forests. The mean percentage of distinguishable genotypes (PD) was 0.80 in meadow plots and 0.36 in forest plots, and the detected genets were smaller in meadow plots than in forest plots. Mean genetic diversity measured as percentage of polymorphic bands, Shannon’s information index and Nei’s gene diversity was also higher in meadows (44.4, 0.22 and 0.14) than in forests (25.1, 0.09 and 0.05). The higher level of clonal diversity in meadow plots is most likely due to the effects of disturbance by mowing, which increases the dispersal of bulbils and promotes the establishment of new plants in meadows compared to forests.  相似文献   

15.
We studied the vegetation, stand structure and communities of above-ground nesting bees and wasps in 45 orchard meadows that were grazed, mown or abandoned (15 of each) in an agricultural landscape near Göttingen, Germany. Total species richness of plants was significantly lower and the proportion of dead wood was significantly higher on abandoned meadows compared to mown or grazed meadows. Species richness of bees, eumenid wasps and sphecid wasps did not differ between the three management types. Abundance of sphecid wasps was significantly higher on abandoned than on managed orchard meadows. Landscape context did not affect management type. The results suggest that management practises affect vegetation more significantly than the studied insect groups.  相似文献   

16.
Du F  Liang Z S  Xu X X  Shan L  Zhang X C 《农业工程》2007,27(5):1673-1683
In order to have a basic knowledge of revegetation, one needs to deepen his understanding of the interactive effects of vegetation and soil. In this article, aboveground biomass, soil nutrients and moisture of 36 old-fields with different abandonment ages (from 2 to 45 years after abandonment), aboveground biomass of 4 typical old-fields, and growth characteristics of 7 predominant old-field species were measured. Changing pace, trend and relationship of community aboveground biomass and soil nutrition during the secondary succession were evaluated; effects of soil nutrition on community aboveground biomass were analyzed using multivariable analysis and pathway analysis, and effects of aboveground biomass on soil nutrition were further discussed. The results show that: (1) Soil nutrients, including organic matter, total nitrogen, total phosphorus, total potassium, nitrate nitrogen, ammonium nitrogen, active phosphorus and active potassium, have the same changing pace and trends as the aboveground biomass. In the process of secondary succession, both the soil nutrition and the community aboveground biomass decreased in the earlier abandonment stage of succession and then increased subsequently. (2) On the basis of the correlation of soil nutrients and abandonment ages, effects of vegetation on 0–20 cm organic matter, active phosphorus, 0–20 cm and 20–40 cm nitrate nitrogen nutrition are significant, while on the basis of the correlation of soil nutrition and aboveground biomass, no significant effects were observed. Hereinbefore, aboveground biomass accounts for only a part of vegetation-soil nutrition effects. The effects of biomass on organic matter, total nitrogen, total phosphorous, total potassium, nitrate nitrogen, active potassium and phosphorous are positive, whereas for ammonium nitrogen it is negative. (3) Abandonment ages, total nitrogen, total potassium, active potassium and soil moisture fluctuation have direct positive effects on the aboveground biomass of old-field communities; abandonment and soil moisture fluctuation have lager effects. Each ingredient of soil nutrition has relatively small effect, among which total nitrogen has larger effects than total and active potassium. The changes in aboveground biomass of old-field communities during succession are caused mainly by the changes in coverage and ecological characteristics of community species (the relatively larger direct effects of abandonment ages), and secondly by the soil moisture fluctuation (the relative smaller indirect effect of abandonment ages through soil moisture). (4) As a dependent variable, belowground biomass approaches power function of soil depth and declines in deeper layer. The root/shoot ratio of communities tends to increase in later succession stages, which also has an increasing tendency. These may influence the accumulation of biomass and decomposition of organic matter, and the vegetation-soil effects may be different.  相似文献   

17.
In order to have a basic knowledge of revegetation, one needs to deepen his understanding of the interactive effects of vegetation and soil. In this article, aboveground biomass, soil nutrients and moisture of 36 old-fields with different abandonment ages (from 2 to 45 years after abandonment), aboveground biomass of 4 typical old-fields, and growth characteristics of 7 predominant old-field species were measured. Changing pace, trend and relationship of community aboveground biomass and soil nutrition during the secondary succession were evaluated; effects of soil nutrition on community aboveground biomass were analyzed using multivariable analysis and pathway analysis, and effects of aboveground biomass on soil nutrition were further discussed. The results show that: (1) Soil nutrients, including organic matter, total nitrogen, total phosphorus, total potassium, nitrate nitrogen, ammonium nitrogen, active phosphorus and active potassium, have the same changing pace and trends as the aboveground biomass. In the process of secondary succession, both the soil nutrition and the community aboveground biomass decreased in the earlier abandonment stage of succession and then increased subsequently. (2) On the basis of the correlation of soil nutrients and abandonment ages, effects of vegetation on 0–20 cm organic matter, active phosphorus, 0–20 cm and 20–40 cm nitrate nitrogen nutrition are significant, while on the basis of the correlation of soil nutrition and aboveground biomass, no significant effects were observed. Hereinbefore, aboveground biomass accounts for only a part of vegetation-soil nutrition effects. The effects of biomass on organic matter, total nitrogen, total phosphorous, total potassium, nitrate nitrogen, active potassium and phosphorous are positive, whereas for ammonium nitrogen it is negative. (3) Abandonment ages, total nitrogen, total potassium, active potassium and soil moisture fluctuation have direct positive effects on the aboveground biomass of old-field communities; abandonment and soil moisture fluctuation have lager effects. Each ingredient of soil nutrition has relatively small effect, among which total nitrogen has larger effects than total and active potassium. The changes in aboveground biomass of old-field communities during succession are caused mainly by the changes in coverage and ecological characteristics of community species (the relatively larger direct effects of abandonment ages), and secondly by the soil moisture fluctuation (the relative smaller indirect effect of abandonment ages through soil moisture). (4) As a dependent variable, belowground biomass approaches power function of soil depth and declines in deeper layer. The root/shoot ratio of communities tends to increase in later succession stages, which also has an increasing tendency. These may influence the accumulation of biomass and decomposition of organic matter, and the vegetation-soil effects may be different.  相似文献   

18.
Abstract. The effects of different forms of land use on germination and establishment of the rare fen species Succisella inflexa were investigated in seed introduction experiments in a mown and an abandoned fen meadow in SE Germany. Treatments included abandonment, mowing in fall and mowing with creation of gaps in the moss and litter layer. Floating capacity of seeds was tested in order to estimate potential dispersal by water. On the mown meadow, gaps had a slightly positive effect on germination rates, while greatly increasing seedling survival until the next spring. At the abandoned site, litter inhibited germination, whereas mosses had a negative effect on germination and a positive effect on survival rates during the first year after germination. Both germination and seedling establishment were negatively affected by the presence of slug herbivores. On the abandoned site, no seedlings at all survived until the next spring. Even though seeds of Succisella inflexa were capable to float for several weeks and to germinate thereafter, the situation at the field sites indicates that longdistance dispersal is highly unlikely. Our results showed that not only direct effects of abandonment, such as accumulation of litter, may have led to poor germination and poor seedling establishment of the species. Additionally, indirect consequences of changes in land use, such as higher seedling herbivory by slugs and successional vegetation changes due to abandonment, were important in determining habitat quality and availability of microsites for seedling recruitment. Furthermore, early mowing imposed seed limitation on plant populations.  相似文献   

19.
Summary. The abandonment of traditional mowing methods of mountain meadows in the Czech Republic at the end of the last century has resulted in secondary re-colonization of these areas. Altered accumulation of plant biomass resulted in a deceleration of N turnover. A mountain meadow may be regarded as a N-limited ecosystem in which plant nutrition is dependent on direct uptake of soil amino acids. The composition and distribution of ammonium ions, nitrate ions and the 16 bio-available proteinaceuous amino acids were investigated in the top 7 cm of the Ah horizon of a Gleyic Luvisol in a long-term moderately mown meadow and an eleven year old, abandoned or uncut meadow. Ammonium N has a dominant role in both ecosystems. The moderately mown meadow showed accelerated N-turnover and higher net ammonization. The plant community showed a dependence on this form. Plant utilization of nitrates and amino acids appeared to be negligible. The uncut or abandoned meadow showed net ammonization from May (start of the experiment) through August, after which plant N-uptake consisted only of amino acids due to microbial immobilization. The release of bio-available nitrogen from spring until the beginning of summer in the Ah horizon was too low to explain total plant N-uptake. Glutamic acid, arginine and aspartic acids had the highest concentrations of any of the amino acids analyzed. Authors’ address: Pavel Formánek, Department of Geology and Pedology, Mendel University of Agriculture and Forestry, Zemedelska 3, 613 00 Brno, Czech Republic  相似文献   

20.
Question: Which environmental and historical variables affect epiphytic lichen diversity in managed and unmanaged wooded meadows? Location: The island of Gotland located in the Baltic Sea east of the Swedish mainland. Methods: We examined total epiphytic lichen diversity (crustose, foliose and fruticose species) on 1148 trees in eight grazed, eight traditionally managed (mowing, hay gathering and pollarding) and seven unmanaged wooded meadows. In addition to management, data on site location, habitat structure, history and adjacent habitat were analysed. Results: Lichen species richness increased with wooded meadow area and was greater within managed sites than in unmanaged meadows. Historic crown cover (ca. 1930) also influenced present‐day lichen richness. Geographic location, distance to sea, wooded meadow area and average tree circumference were important determinants of lichen species composition. Tree circumference was the strongest overall predictor of the number of species on individual trees. However, tree circumference interacted with management regime, whereby cessation of management appeared to reduce species richness most on large trees. Traditionally managed sites, on average, supported the greatest richness of red‐listed species. Conclusions: Management regime, wooded meadow area and canopy cover were the main drivers of lichen species richness, while geographic location, wooded meadow area, distance to sea and average tree circumference were important determinants of species composition.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号