摘要:

The factors influencing the distribution ofCymbopogon validusin Mkambati Game Reserve were investigated using multivariate techniques.C. validuswas found to be present on nutrient‐rich, clay soils and absent from dystrophic, sandy soils. This could account for the patchy distribution ofC. validusin the reserve and may limit its expansion into the surrounding grasslands. There was no correlation between measured soil variables and the density and size ofC. validusplants withinC. validussites.

ISSN:1022-0119    

DOI:10.1080/10220119.1994.9638346

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Ecological theory can help range scientists to understand the determinants of ecological animal density or, in range management terms, ‘carrying capacity’. The relation between the relative density of resources and herbivore density is illustrated by regressions of the ecological density of kudu (Tragelaphus strepsiceros) on the relative density of habitat patches within landscapes for a semi‐arid savanna. Habitat suitability models were used to isolate patches of suitable kudu habitat for each landscape. The habitat suitability models were used to classify a proportion of randomly located circular plots as kudu habitat. The relative density of habitat patches within the respective landscapes was thus determined. The relation between kudu density and the relative density of habitat patches in each landscape was significant, with exponential models producing more significant statistics than linear models. Regressions of resource density against animal density are useful to understand ‘carrying capacity’ for wild herbivores, and additionally provide insights into temporal fluctuations in animal numbers. The usefulness of the approach depends on correctly defining the size of a habitat patch and selecting an appropriate scale of study.

ISSN:1022-0119    

DOI:10.1080/10220119.1994.9638347

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A plotless vegetation sampling technique (ellipse‐intercept method) is described and its accuracy and precision compared by simulation models with two other line‐based techniques: line‐intercept and a point‐intercept method (which measure species covers). The ellipse‐intercept method provides three measures of plant abundance (percentage cover, density and intercept frequency) and also provides plant size distributions, yet requires no more sampling effort than the line‐intercept method. A field test of the three techniques in succulent karoo, showed that the discriminating power per metre of ellipse‐intercept survey (for all three abundance measures) is the same as that of each metre of line‐intercept survey or each four points of point‐intercept survey. The additional ellipse‐intercept information of plant densities and size distributions is shown to be useful for interpreting vegetation differences and for revealing differences (e.g. in vegetation dynamics) not detectable by measures of species covers alone.

ISSN:1022-0119    

DOI:10.1080/10220119.1994.9638348

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We evaluate the ability of existing models of vegetation dynamics to explain how drought and herbivory by domestic livestock can change Karoo vegetation, and why the vegetation does not always return to its original composition when livestock are withdrawn. Using published data for the arid southern and semi‐arid eastern Karoo, we provide new conceptual models of the dynamics of these vegetation types and discuss their relevance for research into the conservation and rehabilitation of Karoo rangelands.

ISSN:1022-0119    

DOI:10.1080/10220119.1994.9638349

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Five plots on sandy soil were thinned to differing tree densities. Three subhabitats were distinguished,viz. under leguminous trees, under non‐leguminous trees, and between tree canopies. Soil under both leguminous and non‐leguminous trees was richer in nutrients (% total N,%organic C, Ca, K, Mg) than between tree canopies. Certain nutrients (K, Mg) also differed between the two canopied subhabitats. The leguminous tree subhabitat had a marginally higher grass biomass than the non‐leguminous tree and the uncanopied subhabitats at high tree densities. This increase was associated with the occurrence ofPanicwn maximum. Digitaria erianthashowed no subhabitat preference, whilstEragrostis lehmannianaandSchmidtia pappophoroideswere mostly confined to the subhabitat between tree canopies. Increased tree competition negatively influenced the yield of grasses between tree canopies, but grass yields associated with the canopied subhabitats were only affected at the highest tree densities. Potential tree competitiveness was the most important determinant of grass yield. The importance of N as the main determinant of thePanicum‐tree association was not confirmed by this study.

ISSN:1022-0119    

DOI:10.1080/10220119.1994.9638350

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1994.9638351

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1994.9638345

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor