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21.
Shiro Tsuyuzaki 《Ecological Research》1989,4(2):167-173
In 1987, a study on buried seed populations was conducted in the crater basin of Mt. Usu, a volcano located in northern Japan,
where the vegetation had beeen almost completely destroyed by eruptions in 1977 and 1978. The former vegetation had consisted
of grassland and broad-leaved forest. In the areas formerly occupied by this grassland and forest, 2128.0 and 1985.3 seeds
per square meter, respectively, were extracted from 12 blocks of the former topsoil using a floattion method. This revealed
that many seeds were still viable even after ten years of burial under thick volcanic deposits. The seeds were distributed
more in sandy soil than in rocky soil of the former topsoil. Twenty-five species, most of which favored grassland, were detected
in both the former grassland and forest. From comparison of α-and β-diversities between the grassland and forest, the structure
of the buried seed population was considered likely to have been more diverse in the forest than in the grassland. The determinants
of composition of the buried seed populations were discussed with reference to the former vegetation and soil characteristics. 相似文献
22.
Growth of Pyrola rotundifolia ssp. maritima in relation to shade 总被引:2,自引:2,他引:0
23.
Plant growth in the extremely arid southern part of the Eastern Desert of Egypt is supported by the torrential moisture stored in the subsurface layers of wadi-fill deposits. The space-time stratification of the soil moisture and corresponding adaptive stratification of root systems lead to the niche separation of the species. The survivorship of all studied plants except Zilla spinosa, has a low mortality at early and middle life, but a rapid change to high mortality at a later stage. Zilla spinosa shows the high juvenile and low adult mortality which related significantly to the population density. 相似文献
24.
Distribution and hydraulic significance of large woody debris in a lowland Australian river 总被引:1,自引:1,他引:0
The line-intersect technique was used to measure the loading of large woody debris in a 1.8 km reach of the Thomson River, Victoria (catchment area of 3540 km2). A debris census (measuring every item present) was done over 0.775 km of this reach. The transect technique over-estimated the actual loading revealed by the census. The loading of debris 0.01 m in diameter for the total 1.8 km reach was 0.0172 m3 m–2, which is higher than that measured in many headwater streams in other parts of the world. The volume loading of debris measured from low level aerial photographs was only 4.8% of the value estimated by the line-intersect technique. The line-intersect estimates were biased due to non-random orientation of debris in the stream (causing estimated errors of +8% for volume loading and +16% for surface area loading). It is recommended that to avoid this problem, when using the line-intersect transect technique in lowland rivers, each line should comprise at least two obliquely-angled transects across the channel. The mean item of debris (0.1 m in diameter) had a trunk basal diameter of 0.45 m, a length of 7.4 m, and volume of 0.7 m3. The riparian trees and the in-channel debris were of similar dimensions. The debris tended to be close to the bed and banks and was oriented downstream by the flow at a median angle of 27°. Because of this orientation, most debris had a small projected cross-sectional area, with the median value being only 1 m2. Thus, the blockage ratio (proportion of projected area of debris to channel cross-sectional area) was also low, ranging from 0.0002 to 0.1, with a median value of 0.004. The average item of debris, which occupied only 0.4% of the cross-section, would have minimal influence on banktop flow hydraulics, but the largest items, which occupied around 10%, could be significant. Judicious re-introduction of debris into previously cleared rivers is unlikely to result in a large loss of conveyance, or a detectable increase in flooding frequency. 相似文献
25.
A methodology is proposed for assessing the ecological value of streams in the catchment of the Moravská Dyje River. It is concluded that by using a wide range of parameters that a more objective assessment is achieved than if only one were used. The landscape of the catchment studied contains excessive amounts of nutrients and, in comparison to its natural state, has become too uniform. 相似文献
26.
Forest density expressing the stocking status constitutes the major stand physiognomic parameter of Indian forest. Density
and age are often taken as surrogate to structural and compositional changes that occur with the forest succession. Satellite
remote sensing spectral response is reported to provide information on structure and composition of forest stands. The various
vegetation indices are also correlated with forest canopy closure. The paper presents a three way crown density model utilizing
the vegetation indices viz., advanced vegetation index, bare soil index and canopy shadow index for classification of forest
crown density. The crop and water classes which could not be delineated by the model were finally masked from normalized difference
vegetation index and TM band 7 respectively. The rule based approach has been implemented for land use and forest density
classification. The broad land cover classification accuracy has been found to be 91.5%. In the higher forest density classes
the classification accuracy ranged between 93 and 95%, whereas in the lower density classes it was found to be between 82
and 85%. 相似文献
27.
Gary Brown 《Plant Ecology》1994,115(1):77-90
The vegetation at various sites within two separate areas (Mechernich and Aachen) of the Eifel Mountains, Germany/Belgium, both characterized by elevated concentrations of heavy metals in their soils, was surveyed in order to investigate the relationships between soil chemical attributes and floristic composition. In both areas, the typical heavy metal communities can form distinct zones, clearly separated from the surrounding heavy metal-sensitive vegetation. However, an intergrading of heavy metal-tolerant and-sensitive vegetation types is not uncommon and such overlaps can occupy large areas. In Mechernich, soil toxicity is primarily determined by the effects of lead, which is best expressed in terms of the Pb/Ca ratio rather than the absolute levels of this metal in the soil. Soils of heavy metal-sensitive vegetation types have a low Pb/Ca ratio, whereas it is considerably higher in areas supporting heavy metal vegetation. Zinc appears to exert little influence on the floristic composition of the investigated vegetation types. In Aachen, zinc is the predominant heavy metal determining vegetation development. Absolute zinc levels of soils do not accurately reflect zinc toxicity. Analogous to the role of the Pb/Ca ratio in the Mechernich area, the Zn/Ca ratio not only separates heavy metal-sensitive and highly tolerant vegetation units, but also gives a good indication of the gradient operating between the two vegetation types. Lead is probably only of local importance in influencing species composition. 相似文献
28.
An ecosystems approach to base-rich freshwater wetlands,with special reference to fenlands 总被引:1,自引:1,他引:0
Geert van Wirdum 《Hydrobiologia》1993,265(1-3):129-153
A survey of base-rich wetlands in The Netherlands is presented. The main area of their occurrence is the low-lying Holocene
part of the country, until some thousand years ago a large and coherent wetland landscape: the Holland wetland. The development
of various parts of the Holland wetland into marshes, fens and bogs can be understood from hydrological relations in mire
basins, as recognized in the distinction of primary, secondary and tertiary mire basin stages. Presently, the remnants of
the Holland wetland are separate base-rich wetlands. The succession of their vegetation reflects various abiotic conditions
and human influences. Three main developmental periods are distinguished as regards these factors. The first, geological period
of mire development is seen as a post-glacial relaxation, with the inertia due to the considerable mass of wetland as a stabilizing
factor. Biological “grazing” influences, as an aspect of utilization by humans, converted base-rich wetlands to whole new
types in the second, historical period. Presently, mass and harvesting have decreased in importance, and actual successions
in terrestrializing turbaries seem to reflect rapidly changing environmental conditions. Human control could well become the
most important factor in the future development of wetland nature. The present value of open fen vegetation strongly depends
on the continuation of the historical harvesting. The development of wooded fen may help to increase the mass of wetland in
the future. Best results in terms of biodiversity are expected when their base state is maintained through water management.
The vegetation and hydrology of floating fens in terrestrializing turbaries is treated in some more detail. Various lines
and phases in the succession are distinguished. Open fen vegetation at base-rich, yet nutrient-poor sites is very rich in
species threatened elsewhere. The fast acidification of certain such fens is attributed to hydrological and management factors.
This acidification is illustrated in the profile of a floating raft sample. At the scale of these small fens, the elemental
structure comprising base-rich fen, transitional fen and bog vegetation, is not as stable as it was in the large Holland wetland.
A critical role seems to be played by the supply of bases with the water influx. The changing base state is supposed to change
the nutrient cycling to such an extent that it would be correct to call this trophic excitation of the ecosystem, rather than
just eutrophication. Eutrophication indicates a quantitative reaction to an increased nutrient supply, the internal system
being unaltered. The drainage of fens, resulting in an increased productivity of the vegetation, provides another example
of excitation, to the effect that the functional system is dramatically changed internally. 相似文献
29.
Hui Yang Seth M. Munson Chris Huntingford Nuno Carvalhais Alan K. Knapp Xiangyi Li Josep Peñuelas Jakob Zscheischler Anping Chen 《Global Change Biology》2023,29(8):2351-2362
Negative extreme anomalies in vegetation growth (NEGs) usually indicate severely impaired ecosystem services. These NEGs can result from diverse natural and anthropogenic causes, especially climate extremes (CEs). However, the relationship between NEGs and many types of CEs remains largely unknown at regional and global scales. Here, with satellite-derived vegetation index data and supporting tree-ring chronologies, we identify periods of NEGs from 1981 to 2015 across the global land surface. We find 70% of these NEGs are attributable to five types of CEs and their combinations, with compound CEs generally more detrimental than individual ones. More importantly, we find that dominant CEs for NEGs vary by biome and region. Specifically, cold and/or wet extremes dominate NEGs in temperate mountains and high latitudes, whereas soil drought and related compound extremes are primarily responsible for NEGs in wet tropical, arid and semi-arid regions. Key characteristics (e.g., the frequency, intensity and duration of CEs, and the vulnerability of vegetation) that determine the dominance of CEs are also region- and biome-dependent. For example, in the wet tropics, dominant individual CEs have both higher intensity and longer duration than non-dominant ones. However, in the dry tropics and some temperate regions, a longer CE duration is more important than higher intensity. Our work provides the first global accounting of the attribution of NEGs to diverse climatic extremes. Our analysis has important implications for developing climate-specific disaster prevention and mitigation plans among different regions of the globe in a changing climate. 相似文献
30.