摘要:

We investigated the feeding responses of a generalist grasshopper, the brown locust (Locusta pardalina), to leaves of the grassEragrostis chloromelasdiffering in polyphenol content. For three specimens ofE. chloromelas, the presence of condensed tannin in epidermal cells was confirmed by histochemical staining, while two specimens lacked polyphenols. Locusts selected the leaves of tannin‐free plants for feeding significantly more frequently than leaves from plants containing tannins. Findings suggest that the food choice of some locusts was affected by the presence of tannins, although variability in feeding responses among individuals was apparent. However, we cannot exclude the possibility that other differences existed between the specimens.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647863

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The relative effects of drought and heavy grazing on the floristic composition, population size and structure, and basal cover of an African savanna grassland were differentiated by comparing changes over eight years, which included a severe drought year, across a gradient of grazing history. Drought had an overriding effect on community change, but grazing history had an additional effect. Severe drought in combination with a history of severe grazing transformed grassland of predominantly palatable, perennial grasses (Themeda triandra, Setaria incrassata, Heteropogon contortus) to grassland dominated by the unpalatable perennialAristida bipartita, annual grasses and forbs. Palatable species were almost eliminated from the sward between tree canopies, but residual populations were protected beneath certain woody species. The most lightly grazed grassland maintained its character of palatable, perennial grass species but was changed considerably in the relative proportion of these species. After the drought, tuft size of palatable species was smaller than any previously recorded but recovered thereafter. A number of annual and perennial grass species were recorded for the first tune subsequent to the drought. Consideration of the life history attributes of species was useful for predicting species’ responses. Grazing management during drought episodes would seem critical for determining the direction of community change. The notion that savanna grasslands are insensitive to grazing because of their disequilibrium behaviour was rejected.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647864

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Owing to the difficulty of examining succession theory in the Karoo, it is suggested the ecological index method (EIM), be replaced by the grazing index method (GIM), through the introduction of grazing index values (GIV) for Karoo plant species. The GIM may provide more acceptable range condition scores and more realistic estimates of the current grazing capacity. Using GIVs, arrived at by scoring the agronomic attributes of the plant species (productivity, forage value, perenniality), the estimated current grazing capacities are found to be closely similar to the grazing capacity norms established for the different agro‐ecological areas in the Karoo. The manner in which the range condition survey is conducted and the application of the grazing index method, ensures the computation of a figure representative of the agronomic potential of the area to support livestock. The cover figure and the range condition score determined for a sample site, can be employed in monitoring the trend in changes in the vegetation, brought about by climatic and biotic variables. Grazing capacity norms are closely related to median annual precipitation (r2= 0.98). The GIM is more closely related to grazing capacities than the EIM (r2= 0.96 and 0.68 respectively).

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647865

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Sixteen promising forage legume accessions (15 species) were selected from small plot observation trials for agronomic evaluation over three years in a subhumid zone of Uganda.Macrotyloma axillare(Archer) significantly out yielded all other accessions in terms of annual dry matter production but not in terms of seed production.Stylosanthes guianensisILCA 163,Clitoria ternateaandCentrosema pascuorumperformed best for the tested attributes and were recommended for further agronomic and animal evaluation, albeit their introduction into Uganda is recent.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647866

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The objective was to evaluate the efficiency and repeatability of the point‐centred‐quarter method. The parameter which was most efficiently sampled was species composition (relative density) with 90% replicate similarity being achieved with 100 point‐centred‐quarters. However, this technique cannot be recommended, even for research purposes, because: (1) the technique is extremely time‐consuming (i.e. it takesc. 14.2 man hours to record 100 samples); (2) it is difficult to identify individual plants because of the multi‐stemmed nature of the vegetation; and (3) there are mathematical constraints with determining density from distance‐based methods.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647867

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Grazing trials at two sites in the semiarid savanna of KwaZulu‐Natal were stocked with cattle at light (0.17 LSU ha‐1), intermediate (0.23 LSU ha‐1) and heavy (0.30 LSU ha‐1) stocking. Pasture disc meter data collected over 116 three‐week periods were used to develop a step‐wise multiple linear model to predict the amount of residual herbage at the end of the summer growing season and the period (days) over which forage supplementation would be required to maintain animal mass during the winter dormant season. Residual herbage mass at the end of summer was significantly related to cumulative summer grazing days, rainfall and range condition (indexed as the sum of the proportions ofThemeda triandra, Panicum maximumandP. coloratum). The period of forage deficit during which herbage mass declined below a grazing cut‐off of 1 695 kg ha‐1was significantly related to residual herbage mass at the end of summer.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647868

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Precise costing of vegetation surveys has become a necessity for parastatal research organizations. Competitive and cost‐effective budgets have to be tabled by these parastatals to secure funding for mapping and classification projects. The mean time required to record floristic data in the Sourish Mixed Bushveld, Transvaal, South Africa, using a recently developed, point‐canopy intercept method (PCIM) and a quadrat method (QM) was 20.5 minutes per stand (SD=5.8) and 45.6 minutes per stand (SD ‐ 11.9) respectively for the whole survey (n = 75 stands). Less time per species encountered was spent using the QM than the PCIM, but because the whole stand (circle with radius of 8 m) was sampled using the QM, more species per stand were recorded for the QM (mean = 60.4; SD ‐ 14.3) than for the PCIM (mean = 16.4; SD = 4.7). Linear regressions of species number versus time taken for the beginning and middle and end of the survey data sets were generated for both methods with correlation coefficients (r) of 0.900 and 0.901 respectively. These models will provide a basis for managers to budget more reliably.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647869

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This study was undertaken mainly to attempt to understand why Italian type plants ofLolium multiflorumLam. (Italian ryegrass) fail to become vernalized in certain climatic regions of South Africa. The vernalization requirements of seed and plants for the induction of flowering and seed production were determined.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647870

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

N fertilizer was applied as a single dressing in spring at 0, 20, 40, 80, 160 and 320 kg N ha‐1a‐1to an establishedDigitaria erianthapasture, previously used as a hay crop. The only significant increase in dry matter (DM) yield was obtained with 80 kg ha‐1a‐1. The DM production per unit of nitrogen (N) applied also reached a maximum with 80 kg N ha‐1a‐1. The distribution of rainfall also influenced DM yield.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647871

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The quantification of defoliation effects on grass vigour is important in understanding veld response to differential management. Effect of grazing on vigour can be determined by measuring regrowth during the season following grazing and comparing treatments with an undefoliated control. In this study, veld was defoliated at varying intensities and frequencies. During the following season, regrowth was measured on all treatments to quantify any residual treatment effects on vigour. Comparisons between measuring yield per tuft and yield per unit tuft basal area of this regrowth revealed marked discrepancies between the methods. These findings were in agreement with previously reported studies. In addition, differences between the mean tuft basal areas were found between treatments. Differences in vigour may reflect a change in tuft area as well as amount of growth per unit tuft area. Quantification of residual effects of grazing on plant vigour should thus logically be done using techniques based on plant yields, rather than on the basis of yield per unit tuft basal area. Techniques are available for the measurement of regrowth of all species present using quadrats, and this measure, expressed as species yield per unit land area, gives extra significance to the results.

ISSN:1022-0119    

DOI:10.1080/10220119.1995.9647872

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor