多年生黑麦草草地生态系统中放牧强度对草地结构及组织转化的影响

研究了放牧强度对多年生黑麦草人工草地蘖的形态、密度、草地生产率及组织转化的影响。结果表明,重牧条件下蘖密度大于轻牧,而轻牧的单株蘖重大于重牧。重牧划地净生产率大于轻牧,主要是由于轻和手条件下,草地的高的生长率被更高的枯死率所抵消。春夏之交,采用灵活的管理措施,转换放牧强度可以提高草地的生产率。     

Effects of fire on abundance of Eragrostis intermedia in a semi-arid grassland in southeastern Arizona

Abstract. Eragrostis intermedia (Plains lovegrass) is a midheight perennial bunchgrass native to semi-arid grasslands of the southwestern USA, that becomes an abundant and dominant component of these grasslands in areas long protected from livestock grazing. Substantial mortality of plains lovegrass occurred on a large livestock exclosure in southeastern Arizona, after a period of declining precipitation, but only in areas that had not burned in the previous three years. Lovegrass abundance subsequently increased on both undisturbed and burned sites, but remained substantially higher on the burned area. Long-term abundance of plains lovegrass may depend on episodic fire, particularly during periods of reduced precipitation.     

The influence of habitat structure on arthropod diversity in Argentine semi-arid Chaco forest

Abstract. The Argentine Chaco is a mosaic of grassland and open forest habitats maintained by natural disturbance activities such as fire. Since the introduction of domestic livestock and other human activities, the balance of this mosaic has been significantly altered, both in plant species and structural composition. This study focuses on the impact of such changes on the diversity of ground-dwelling arthropods within semi-arid Chaco forest. Quantitative measures of habitat structure and arthropod diversity were taken in forest areas previously subjected to grazing, logging and ploughing. Results indicated that arthropod diversity was smaller on sites with reduced structural complexity, with marked changes in arthropod family composition. The habitat components relating to plant architectural and vertical diversity were particularly influential on arthropod diversity. The guild size ratio of predatory to non-predatory arthropods also differed significantly between habitats suggesting a change in the resource base available to some groups. The latter suggests a shift in the functional organisation of the forest ecosystem which could have important repercussions for the diversity of other trophic levels.     

Multivariate analysis of the vegetation of the volcanoes Tláloc and Pelado,Mexico

Abstract. Multivariate analysis was used to describe the composition and distribution of vegetation types on the slopes of the volcanoes Tláloc and Pelado, Mexico. These volcanoes are situated in the transitional zone between the Holarctic and Neotropical floristic regions, which offers a partial explanation for the relatively high α and β diversities. Previous research argued that human activities, i.e. burning and grazing, rather than abiotic factors, play a major role in determining the distribution and floristic composition of the vegetation. TWINSPAN, Detrended Correspondence Analysis and Canonical Correspondence Analysis were used to test this hypothesis. Floristic and environmental data from 138 relevés and seven explanatory environmental variables were included: elevation, soil depth, soil moisture, percentage litter cover, percentage cover of bare ground, burning and grazing were included in the analysis. Soil moisture and elevation accounted for ca. 63% of the residual inertia and none of the remaining explanatory variables proved to be correlated significantly with the first two axes. The present results suggest that burning and grazing operate on a finer scale. In conclusion, soil moisture and elevation are the most relevant variables to explain the distribution of the vegetation under study.     

不同放牧强度下高寒灌丛植物的生长特点

 不同放牧强度下高寒灌丛植物在生长发育、生理生态,物质生产和群落结构等方面主要有以下变化：1．在高寒灌丛草场,禾草类、莎草类和灌丛类植物的叶面积指数和平均生长速率随着放牧强度的减轻而增大;随着放牧强度的增加而减小。植株平均高度,植被盖度水平也与放牧强度呈负相关(p<0.01)。2．各项生长分析参数中：叶面积比率(LAR)、叶面积干重比(SLA)和叶干重比(LWR)与放牧强度之间存在负相关。叶面积指数(LAI)与地上生物量呈正相关(p<0.5),地上部现存在量与放牧强度呈负相关(p<0.01)。3．不同放牧强度条件下,高寒灌丛中的禾草类、莎草类、灌丛类和杂类草植物的种类组成和数量变化明显。其中禾草类和莎草类、灌丛类植物的生物量和种类组成比例在重度放牧下减少,在轻度放牧下增大。反之,重度放牧下杂类草的组成和数量明显增加,而轻度放牧下其比例降低。     

The effects of grazing on the pollen production of grasses

Samples from moss polsters taken over three consecutive years during a controlled grazing experiment in a nature reserve in the Netherlands were analysed for their pollen content, particularly grass pollen. Samples were also taken in the year following the experiment, with grazing pressure strongly diminished. This yielded data regarding the effect of grazing on the pollen production of grasses in open habitats, plantations, and unproductive and productive woods under different grazing pressures.     

Ecosystem responses to changes in plant functional type composition: An example from the Patagonian steppe

Abstract. Grass cover along a grazing intensity gradient in Patagonia decreases, whereas bare soil and shrub cover increases. Our objective was to study the effect of a change in the dominant plant functional type on soil water balance, primary production, herbivore biomass, roughness, and albedo. Using a soil water balance model, we found increases in evaporation and deep drainage, and a decrease in total transpiration along the grazing intensity gradient. Above-ground primary production, estimated from transpiration, decreased along the grazing intensity gradient because shrubs did not fully compensate for the decrease in grass production. Using a statistical model, we calculated herbivore biomass from estimates of above-ground primary production. Estimated herbivore biomass was lowest in the shrub-dominated extreme of the grazing gradient. Roughness increased from the grass-dominated to the shrub-dominated community. Albedo had a maximum at an intermediate position along the gradient. Our results suggest that changes in plant functional type composition, independent of changes in biomass, affect ecosystem functioning and the exchange of energy and material with the atmosphere. Grasses and shrubs proved to be appropriate plant functional types to link structure and function of ecosystems.     

Fluctuations in a coastal dune grassland due to fluctuations in rainfall: Experimental evidence

Experiments with rainfall on a dune grassland near Oostvoorne, the Netherlands with Festuco-Galietum as the main syntaxon are described. Both increase in rain through additional watering and decrease in rain through catchment are presented to plots belonging to the xerosere and the mesosere. Clear changes in the floristic composition are the result, even after only two years. Typical Festuco-Galietum species are promoted by high rainfall, species of open habitat such as Corynephorus canescens are promoted by drought. The results are discussed against the background of long term permanent plot observations in the area and a relation with rabbit grazing intensity is supposed.Nomenclature of vascular plants follows Heukels-van Ooststroom (1975) Flora van Nederland 18 ed., Woiters-Noordhoff, Groningen; Nomenclature of syntaxa follows Westhoff & den Held (1969). Plantengemeenschappen in Nederland, Thieme, Zutphen.Field work in 1978 was carried out with Frans Bongers and Marc de Lyon, in 1979 with Marc de Lyon, Picter Meeuwissen and Guiljo van Nuland, all then MSc. students at the Division of Geobotany. Their help and the advice of Dr. Peter van der Aart, Institute of Ecological Research, Oostvoorne, are acknowledged.     

Structure and seasonal dynamics of humid tropical grasslands in Meghalaya,India

Abstract. Four humid grassland communities at three different locations in Meghalaya, India were analysed during 1988 and 1989 for species and life-form composition, diversity and dominance in relation to altitude, soil and prevailing disturbances. Due to the adverse interactive influences of exceptionally high annual rainfall (> 10 000 mm), topography and human interference on soil fertility, the grassland at Cherrapunji, at 1300 m altitude, had a low species diversity (H'= 1.74) and was dominated by three perennial grass species. Similar grasslands, at both higher and lower altitudes on fertile soil and with lower rainfall (ca. 2000 mm), showed higher diversity values (H'= 2.28 at Burnihat and 2.31 at Upper Shillong). The proportion of perennial species and chamaephytes increased with elevation. At the high altitude site a grassland under short-term protection from fires and grazing had a higher species richness, density and basal cover than an unprotected grassland. All grasslands show a clear seasonality, albeit with different patterns, with a maximum in density and basal cover in August. The differences in structure and seasonality are discussed in terms of different levels of stress.