| Autor: |
du Toit, Justin C. O., Danckwerts, Jock E., Zacharias, Peter J. K. |
| Předmět: |
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| Zdroj: |
Grassland Science; Jun2007, Vol. 53 Issue 2, p61-67, 7p, 1 Diagram, 4 Charts, 5 Graphs |
| Abstrakt: |
Grass swards that have been grazed by livestock exhibit a patchy structure comprising short and tall components. While such patches are often observed, they are seldom objectively described. This study sought to develop a technique for objectively discriminating between patches (short) and non-patches (tall) in a semiarid savanna in the Eastern Cape, South Africa. Two independent hypotheses were addressed: (i) vegetation can be categorized into patches and non-patches by analyzing data comprising a large number of single measurements of sward height; and (ii) there are two distinct grass communities present, each of which comprises a particular range of sward heights. Single and double normal distributions were fitted to height distributions using the maximum likelihood estimation (MLE; hypothesis 1), and species composition data were ordinated using canonical correspondence analysis (CCA) and two-way indicator species analysis (TWINSPAN; hypothesis 2). In general, the results supported both hypotheses. Patches and non-patches can be distinguished using MLE unless grazing is patchy at a scale smaller than the lowest scale of sward measurement (here 0.5 m, the diameter of a disc pasture meter). Ordination and classification revealed that – at our site – two distinct grass communities are present, and that patches and non-patches are characterized by vegetation <6 and 6 cm, respectively. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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