Tall-grass Communities Research Articles

Numerical syntaxonomy of the tall-forb and tall-grass communities in the Tatra Mountains

Numerical syntaxonomy of the tall-forb and tall-grass communities in the Tatra Mountains

Grazing and the Dynamics of Nutrient and Energy Regulated Microbial Processes in the Serengeti grasslands

Microbial biomasses and N and P mineralization potentials were determined on soils collected from short-, mid- and tallgrass communities along a gradient of increasing rainfall and decreasing grazing intensity in the Serengeti National Park, Tanzania. Total N, organic C, pH and clay content were highest on shortgrass sites which experienced the highest grazing intensities, and declined successively on soils from mid- and tallgrass communities. Microbial biomass ranged across sites from an average of 47.1 ± 6.3 to 315.8 ± 8.4 mg C 100 g dry soil-1, and was directly related to grazing intensity and organic carbon, and inversely related to soil C/N ratio. Net N mineralized over the 20 d incubation period ranged from 1.0 +± 1.3 to 63.4 ± 4.6 ig N g dry soil-' 20 d-1, was a function of both total N and soil microbial biomass, and varied inversely with soil C/N ratio. Periods of net N immobilization lowered the mean mineralization rates in soils from midgrass sites. Net N mineralized ranged from 0.09 ± 0.10% of total soil N at Seronera, the site with the lowest grazing intensity, to 2.24 + 0.17% of total soil N at Southeast Kopjes, a site with high grazing intensity. In order to study microbial growth and the concomitant N and P mineralization responses to varying substrate quality, soil samples were subjected to a laboratory experiment involving untreated soils, and three C amendment treatments which included either glucose, wildebeest dung or plant litter. Dung-amended soils showed higher net N mineralization levels in comparison to litter-amended soils, despite insignificant differences in total respiration. The more efficient utilization of dung compared with plant litter, appeared to be related to more balanced C/nutrient ratios of dung and the energy or nutrient limited site-specific characteristics of microbial growth. On sites of low nutrient availability, the increased flow of P through dung may be important in maintaining accelerated nutrient cycling rates in the grazing food web.

Revegetation of Artificial Disturbances in Grasslands of the Serengeti National Park, Tanzania: II. Five Years of Successional Change

SUMMARY (1) The effects of disturbance-depth and grazing on succession, spatial heterogeneity and species revegetation patterns were investigated in four grasslands (short, mid, tall and mosaic) in the Serengeti National Park, Tanzania. Successional trajectories of vegetation on disturbed and control plots in grazed and ungrazed blocks and plot variability were derived from detrended correspondence analysis. (2) All disturbances were revegetated by species of the original community and returned to their previous compositions 1-3 yr after disturbance. (3) After the elimination of grazing, short and sexually-reproducing species disappeared from the short- and mid-grass communities, which became dominated by tall, vegetatively-reproducing species. The mosaic and tall-grass communities were unchanged. Vegetation on the disturbed plots in both grazed and ungrazed blocks resembled the species composition and structure of the surrounding undisturbed vegetation. (4) Within-treatment plot heterogeneity increased over 5 yr in a community that was dominated by vegetatively-spreading species but decreased in communities dominated by caespitose species. (5) Patterns of colonization and succession in the undisturbed plots supported Gleason's 'individualistic' concept.

A survey of an upland grassland bird community during breeding season

1. A bird census was made during three breeding seasons at Kirigamine grassland plateau, Nagano in central Honshiu.2. Two methods were adopted. One, the line transect census, was used during 1961-63 and the other, the square census in 1963 with an area of 500m2.3. The Grey-headed Bunting, Emberiza fucata, the Japanese Reed Bunting, Emberiza yessoensis, the Black-browed Reed Warbler, Acrocephalus bistrigiceps, and the Stonechat, Saxicola torquata were main species of this grassland habitat. Although they occupied the same area, each species selected the respective niche and there were differences in nest sites and food items.4. As the result of line transect census, the G.-h. Bunting and the Stonechat were uniformly distributed with the densities of 0.3-0.4 pairs and 0.3-0.7 pairs per 100 meters respectively. Although the densities of the B.-b. Reed Warbler were also 0.3-1.2 pairs, this species was much more patchy in distribution than the two others.5. The B.-b. Reed Warblers were found in tall grass community at the lowest level and the G.-h. Buntings bordered them on both sides, while these were again bordered by the Stonechats with some overlap. The Jap. Reed Bunting was most local in distribution along the line transect.6. In the square census, the G.-h. Bunting occurred over the whole study area and the occurrence rates of the other three species, Stonechat, B.-b. Reed Warbler and Jap. Reed Bunting, were below 50%. The Stonechat and the B.-b. Reed Warbler were found localized in somewhat colonial condition on the slopy part and at the tall grass community respectively.7. The 'specific occupied area' was largest in the Jap. Reed Bunting, decreasing in the G.-h. Bunting, the Stonechat to the B.-h. Reed Warbler.8. The Jap. Reed Bunting and the G.-h. Bunting similarly selected the nest site at the root of grasses, the Stonechat at a hollow of the ground with some covering, while the B.-b. Reed Warbler nested at 20-50cm above the ground in taller grasses.9. The breeding seasons in 1963 advanced with the order of Stonechat-Jap. Reed Bunting-G.-h. Bunting-B.-h. Reed Warbler.10. All the species took Lepidoptera larvae for chicks; many adult Diptera were fed by Stonechats and the Jap. Reed Bunting selected adult Lepidoptera, Orthoptera and spiders, while the B.-b. Reed Warbler preferred the Orthoptera.11. Thus, the structure of bird community in this grassland consisted of the Jap. Reed Bunting and G.-h. Bunting preferring the short grass, the Stonechat of abandoned habitat and the B.-b. Reed Warbler restricted to the tall grass.