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Grass Competition (grass + competition)

Distribution by Scientific Domains

Life Sciences	87%

Selected Abstracts

Wyoming Big Sagebrush Density: Effects of Seeding Rates and Grass Competition

RESTORATION ECOLOGY, Issue 2 2002
Mary I. Williams
Abstract The mining industry commonly seeds shrubs and grasses concurrently on coal-mined lands of northeastern Wyoming, but ecological interactions between seeded shrubs and grasses are not well documented. Artemisia tridentata Nutt. ssp. wyomingensis (Beetle and Young) (Wyoming big sagebrush) is the dominant pre-mining shrub on many Wyoming mine sites. Despite past failures to establish Wyoming big sagebrush, the Wyoming Department of Environmental Quality, Land Quality Division's rules and regulations require establishment of 1 shrub per m2 on 20% of post-mined land in Wyoming. A study was established at the Belle Ayr Coal Mine south of Gillette, Wyoming to evaluate the effects of sagebrush seeding rates and grass competition on Wyoming big sagebrush seedling density. Three sagebrush seeding rates (1, 2, and 4 kg pure live seed [pls]/ha; 350, 700, and 1,400 pls/m2, respectively) and seven cool-season perennial grass mixture seeding rates (0, 2, 4, 6, 8, 10, and 14 kg pls/ha; 0, 187, 374, 561, 750, 935, and 1,309 pls/m2, respectively) were applied during winter 1998,1999. Pascopyrum smithii (Rydb.) A. Love (western wheatgrass), Elymus lanceolatus (Scribner & J.G. Smith) Gould (thickspike wheatgrass), and Elymus trachycaulus (Link) Gould ex Shinners (slender wheatgrass) comprised the grass seed mix (equal seed numbers of each species). Sagebrush seedling density differed among sagebrush seeding rates but not among grass seeding rates. On all sampling dates in 1999 and 2000, sagebrush seedling density differed among sagebrush rates and was greatest at the 4 kg pls/ha sagebrush seeding rate. All sagebrush seeding rates provided densities of at least 1 shrub per m2 after two growing seasons. Grass density and production in 2000 suggest that adequate grass production (75 g/m2) was achieved by seeding at 6 to 8 kg pls/ha. Within these grass seeding rates, four or more sagebrush seedlings per m2 were attained when sagebrush was seeded at 2 to 4 kg pls/ha. Use of these seeding rate combinations in mine reclamation can achieve Wyoming big sagebrush standards and reduce reseeding costs. [source]

Acacia species turnover in space and time in an African savanna

JOURNAL OF BIOGEOGRAPHY, Issue 1 2001
William J. Bond
Aim Patterns of species turnover along environmental gradients are better studied than their causes. Competitive interactions, or physiological tolerance are most often cited as determinants of turnover. Here we investigate differential tree species response to disturbance by fire and mammal browsing as causes of changing dominance of species within and among sites along an altitudinal gradient. Methods We documented the distribution of two Acacia species using maps and sample transects. We explored possible causes of species turnover by studying differences between the species in tolerance to grass competition using pot experiments, to browsers by observing patterns of shoot damage, and to fire by comparing the size structure of populations burnt at different frequencies and intensities. Results Acacia karroo woodlands were rare and occur at higher elevations than the much more common A. nilotica woodlands. Woodland composition seems set to change in future since the pattern of dominance was reversed in juvenile stages. A. karroo juveniles were very widespread and far more abundant than A. nilotica juveniles. A. karroo juveniles were most abundant in tall fire-prone grasslands and were rare on grazing lawns whereas A. nilotica showed the reverse pattern. In the pot experiments, growth of both species was suppressed by grasses but there were no significant differences in response between the two species. Juveniles of A. karroo were more heavily browsed than those of A. nilotica. However juveniles of A. nilotica were less tolerant of frequent intense burns than juvenile A. karroo. Main conclusions Disturbance gradients, from high fire frequency and low herbivore density at high altitudes, to lower fire frequency and higher herbivore density at low altitudes, are responsible for the shift in community structure along the spatial gradient. Differential responses to browsing and fire may also explain temporal turnover from A. nilotica in the past to A. karroo in the present. Changes in the area burnt annually, and in faunal composition, suggest a landscape-scale shift from grazing-dominated short-grass landscapes in the 1960s, favouring A. nilotica, to fire-dominated tall grasslands in the 1990s favouring A. karroo. We suggest that species turnover due to differential responses along disturbance gradients may be much more widespread than the current paucity of studies suggests. [source]

Effects of moisture, nitrogen, grass competition and simulated browsing on the survival and growth of Acacia karroo seedlings

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
Keletso Mopipi
Abstract The effects of irrigation, nitrogen fertilization, grass competition and clipping were investigated for one growing season at the research farm of the University of Fort Hare in the Eastern Cape Province of South Africa. The aim of the experiment was to assess the short-term performance of Acacia karroo seedlings under different environmental conditions and the implications of such factors on the long-term recruitment of plant species in savanna rangelands. There were no significant treatment effects on the survival of A. karroo seedlings. Using stem length and basal diameter as growth parameters, it was observed that irrigation enhanced both variables, while nitrogen fertilization did not have any significant effects. Clipping, grass competition and their interaction greatly suppressed the growth of the seedlings. Clipping increased the mean stem length when they were irrigated and fertilized. Control and fertilized plants had the highest stem length in the absence of grass competition, while grass competition combined with clipping resulted in the lowest stem length in both irrigated and nonirrigated plants. It was concluded that in the presence of grass competition, controlled browsing could be a viable solution to the problem of bush encroachment in savanna rangelands. Résumé Les effets de l'irrigation, d'une fertilisation à l'azote, de la compétition avec l'herbe et de la taille ont étéétudiés pendant une saison de croissance dans la ferme expérimentale de l'Université de Fort Hare, dans la Province du Cap oriental, en Afrique du Sud. Le but de l'expérience était d'évaluer les performances à court terme de jeunes plants d'Acacia karroo dans différentes conditions expérimentales, et les implications de ces facteurs sur le recrutement à long terme d'espèces végétales dans des pâturages de savane. Il n'y a pas eu d'effet significatif des traitements sur la survie des plants d'A. karroo. En utilisant la longueur des troncs et le diamètre de la base comme indicateurs de croissance, on a observé que l'irrigation augmentait les deux variables, alors que la fertilisation à l'azote n'avait aucun effet significatif. La taille, la compétition avec l'herbe et leur interaction supprimait fortement la croissance des jeunes plants. La taille augmentait la longueur moyenne des troncs lorsqu'ils étaient irrigués et fertilisés. Les plants témoins et les plants fertilisés avaient les troncs les plus longs en absence de toute compétition avec des herbes, alors que cette dernière, combinée avec la taille, aboutissait à la longueur la plus petite des troncs, chez les plants irrigués ou non. On en a conclu qu'en cas de compétition avec des herbes, un pâturage contrôlé pourrait être une solution viable au problème de l'envahissement des broussailles dans les pâturages de savane. [source]

Wyoming Big Sagebrush Density: Effects of Seeding Rates and Grass Competition

Holocene boundary dynamics of a northern Australian monsoon rainforest patch inferred from isotopic analysis of carbon, (14C and ,13C) and nitrogen (,15N) in soil organic matter

AUSTRAL ECOLOGY, Issue 6 2004
D. M. J. S. BOWMAN
Abstract Soil organic matter (SOM) was sampled from lateritic soil profiles across an abrupt eucalypt savanna,monsoon rainforest boundary on the north coast of Croker Island, northern Australia. Accelerator mass spectrometry dating revealed that SOM that had accumulated at the base of these 1.5 m profiles had a radiocarbon age of about 5000 years. The mean carbon and nitrogen stable isotope composition of SOM from 10 cm deep layers from the surface, middle and base of three monsoon rainforest soil profiles was significantly different from the means for these layers in three adjacent savanna soil profiles, suggesting the isotopic ,footprint' of the vegetation boundary has been stable since the mid Holocene. Although there were no obvious environmental discontinuities associated with the boundary, the monsoon rainforest was found to occur on significantly more clay rich soils than the surrounding savanna. Tiny fragments of monsoon rainforest and abandoned ,nests' (large earthen mounds) of the orange-footed scrubfowl, an obligate monsoon rainforest species, occurred in the savanna, signalling that the rainforest was once more extensive. Despite episodic disturbances, such as tropical storm damage and fires, the stability of the boundary is probably maintained because clay rich soils enable monsoon rainforest tree species to grow rapidly and achieve canopy closure, thereby excluding grass and reducing the risk of fire. Conversely, slower tree growth rates, grass competition and fire on the savanna soils would impede the expansion of the rainforest although high rainfall periods with shorter dry seasons may enable rainforest trees to grow sufficiently quickly to colonize the savanna successfully. [source]

Spatial pattern of dry rainforest colonizing unburnt Eucalyptus savanna

AUSTRAL ECOLOGY, Issue 2 2004
R. J. Fensham
Abstract The spatial pattern of dry rainforest and savanna tree species was analysed in a 1.56-ha plot within an unburnt eucalypt savanna woodland in north Queensland, Australia. Rainforest colonization constituted only 1.3% of the basal area and mostly consisted of individuals less than 3 m high. The distribution of rainforest trees was highly clumped around the large savanna eucalypt trees. Ecological mechanisms generating the clumped distribution are discussed in light of evidence from this study and the literature. Herbaceous biomass was not reduced under trees, suggesting that relief from grass competition has not favoured rainforest colonization under tree crowns. Edaphic facilitation through nutrient enrichment under savanna tree crowns appears to be only minor on the moderate fertility soils of the area. The highly clumped pattern of colonizing dry rainforest may be a consequence of seeds dropped from birds roosting in savanna trees. [source]

Spatial pattern of dry rainforest colonizing unburnt Eucalyptus savanna

AUSTRAL ECOLOGY, Issue 2 2004
R. J. FENSHAM
Abstract The spatial pattern of dry rainforest and savanna tree species was analysed in a 1.56-ha plot within an unburnt eucalypt savanna woodland in north Queensland, Australia. Rainforest colonization constituted only 1.3% of the basal area and mostly consisted of individuals less than 3 m high. The distribution of rainforest trees was highly clumped around the large savanna eucalypt trees. Ecological mechanisms generating the clumped distribution are discussed in light of evidence from this study and the literature. Herbaceous biomass was not reduced under trees, suggesting that relief from grass competition has not favoured rainforest colonization under tree crowns. Edaphic facilitation through nutrient enrichment under savanna tree crowns appears to be only minor on the moderate fertility soils of the area. The highly clumped pattern of colonizing dry rainforest may be a consequence of seeds dropped from birds roosting in savanna trees. [source]