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1.
Classification and ordination of plant communities along an altitudinal gradient on the Presidential Range,New Hampshire,USA 总被引:1,自引:0,他引:1
An analysis of vegetation along an altitudinal gradient on the Presidential Range, New Hampshire, USA, using the Braun–Blanquet approach followed by multivariate data analysis is presented. Twelve main plant communities have been distinguished. Floristic information is presented in twelve tables and one appendix. The relationships of the communities to complex environmental gradients are analyzed using Correspondence Analysis. Floristic composition and community structure are controlled primarily by the altitudinal gradient (temperature, precipitation), and by mesotopographic conditions (snow accumulation, exposure and cryoturbation, slope position, and soil moisture). 相似文献
2.
L. Jerling 《Plant Ecology》1988,74(2-3):161-170
Population fluctuations ofGlaux maritima, along a transect on a Baltle sea shore meadow, were recorded between 1979 and 1983. A bimodal distribution in numbers along the transect reflects the variation in factors regulating numbers: The two maintenance systems of the species, vegetative propagation and sexual reproduction play different roles. Vegetative propagation is fast and responds quickly to variations in the environment. The seeds germinate in strongly fluctuating temperatures which are triggered by disturbances such as flooding, damaging the vegetation. 相似文献
3.
Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causality. 相似文献
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Abstract. Southern Appalachian high-elevation outcrops harbour six regionally rare Northern Appalachian taxa usually considered relicts of a Pleistocene alpine flora. For five of the six taxa, minimum elevation in the south was 367–1113 m higher than in the north. While habitats compared between the two regions share only 9% of their total flora, individual plots had up to 70% of their species occurring in the opposite region. The northern affinity of southern outcrops increased with elevation, slope steepness, soil Cu, B and SO4 and decreased with potential solar radiation and soil Na. As a result, communities above 1600 m on felsic bedrock, and above 1350 m on mafic bedrock, were most northern in composition. Northern affinity of southern outcrops also increased with latitude, which may partly result from closer geographic proximity to past communities that provided progenitors for the current northern flora. Northern treeless habitats increased in southern affinity with increased slope steepness, perennial seepage, vegetation height, shade, soil pH, Al, Mn, Na and decreased elevation and organic matter. As a result, northern outcrop communities below treeline were most similar to those on southern outcrops. This suggests that southern outcrop vegetation may be more similar to Pleistocene outcrop vegetation than to Pleistocene alpine vegetation. Partial constrained ordination showed that while compositional differences between the Northern and Southern Appalachian habitats were largely explained by environmental differences, there was a significant component of residual variation explained by north or south position that was unrelated to environment. These residual compositional differences may result from historical influences on community structure involving stochastic extinction and colonization processes. 相似文献
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Abstract. Goat grazing is examined as a possible tool for grassland management. In this paper, goat grazing preferences are described. The proportion of biomass of particular species eaten by a goat was estimated on the basis of comparison of paired quadrats. The control quadrats were clipped before grazing and their biomass was compared with the biomass in grazed quadrats. Estimates of the proportion consumed were calculated for frequent species; they were significantly different among species; the most preferred species was Polygonum bistorta, a species with broad, soft, nutritious leaves. The least grazed species were Agrostis tenuis and Galium harcynicum. Various indices of food selectivity (e.g. forage ratio, electivity index) were calculated and their behaviour was compared. Canonical Correspondence Analysis and Redundancy Analysis with appropriate covariates reflecting the block design of the experiment were used to evaluate overall changes in species composition and yielded results similar to those from the direct estimation of the proportion consumed. 相似文献
9.
C. Bosco F. Cotelli R. Bonomi P. Mognoni G. S. Roi 《European journal of applied physiology and occupational physiology》1994,69(1):71-74
The effects of heavy resistance training and jumping exercise were examined during the 1989–1990 season in 12 international level alpine skiers. The athletes were tested before, during, immediately after training and during the period off training (June, July, October 1989, April 1990). Their mechanical behaviour was investigated using firstly squat jumps performed without (SJ) or with low extra loads (20 kg, SJ20kg) and high extra loads (equivalent to body mass on the shoulders, SJbm) and secondly 15–30 s continuous jumping. These tests allowed the assessment of explosive dynamic strength production (SJ and SJ20kg), slow dynamic strength (SJbm) and maximal mechanical power (continuous jumping). The training adopted resulted in specific changes in neuromuscular performance; in fact all the variables studied showed a significant improvement (P<0.01) from the beginning compared to the end of training. The range of improvement was between 55.4% (SJbm) and 12.5% (average power during 15-s continuous jumping). The enhancement of SJ had become significant by July. Surprisingly, even when no strength or jumping training was performed during the competition period (November-April), no deterioration in the neuromuscular performance was observed, there being no significant difference between the test values obtained in October 1989 and April 1990. It was concluded that the demanding competition programme of alpine skiers may provide a training stimulus adequate to maintain the neuromuscular improvement induced by training throughout the competition season. 相似文献
10.
Gerd Johansson 《Plant and Soil》1993,151(1):11-20
Distribution of net assimilated C in meadow fescue (Fectuca pratensi L.) was followed before and after cutting of the shoots. Plants were continuously labelled in a growth chamber with 14C-labelled CO2 in the atmosphere from seedling to cutting and with 13C-labelled CO2 in the atmosphere during regrowth after the cutting. Labelled C, both 14C and 13C, was determined at the end of the two growth periods in shoots, crowns, roots, soil and rhizosphere respiration.
Distribution of net assimilated C followed almost the same pattern at the end of the two growth periods, i.e. at the end of
the 14C- and the 13C-labelling periods. Shoots retained 71–73% of net assimilated C while 9% was detected in the roots and 11–14% was released
from the roots, determined as labelled C in soil and as rhizosphere respiration.
At the end of the 2nd growth period, after cutting and regrowth, 21% of the residual plant 14C at cutting (14C in crowns and roots) was found in the new shoot biomass. A minor part of the residual plant 14C, 12%, was lost from the plants. The decreases in 14C in crowns and roots during the regrowth period suggest that 14C in both crowns and roots was translocated to new shoot tissue.
Approximately half of the total root C at the end of the regrowth period after cutting was 13C-labelled C and thus represents new root growth. Root death after cutting could not be determined in this experiment, since
the decline in root 14C during the regrowth period may also be assigned to root respiration, root exudation and translocation to the shoots. ei]{gnH}{fnLambers}
ei]{gnA C}{fnBorstlap} 相似文献