Patterns of vegetation along the Omo River in southwestEthiopia
| 详细信息 | 推荐本文 | |
- 作者：Carr ; Claudia J.
- 关键词：Riverine vegetation ; Tropical forests ; Floodplain ; Omo River ; Ethiopian vegetation
- 刊名：Plant Ecology
- 出版时间：1998
- 出版年：1998
- 期刊代码：97_13850237
- 类别：med
- 卷：135
- 期：2
- 页码：135-163
- 数据来源：sp
摘要
This study investigates the riverine vegetation along the perennialOmo River, which flows from the Ethiopian highlands to its terminus, in thesouthwestern lowlands, at Lake Turkana (formerly Lake Rudolf). Broadlydefined to include the levee backslopes and adjacent mudflats (or ancientfloodplains), the riverine zone in the lower Omo basin supports a relativelyluxuriant vegetation compared with the dry grasslands in the surroundingplains environments. Habitat conditions along the lower Omo have changedsignificantly during the past century, primarily due to a period of reducedrainfall and river flow, a drop in lake level (L. Turkana) at the river'sterminus and increased exposure of natural levees near the Omo's terminus.The floristic and physiognomic character of riverine vegetation were studiedat selected sites, ranging from the relatively straight channel section inthe modern delta to a strongly meandering (upstream) section of the river. Acombination of open canopy woodland, shrub thicket and grassland (withscattered tree emergents) prevailed on the more recently exposed levees, inand near the modern delta; closed canopy woodland and forest predominated onfore levees in the meandering segment. Floristic diversity was relativelylow at all study sites. Ficus sycomorus, Tapura fischeri, Melanodiscusoblongus, Celtis integrifolia and Trichilia roka were most significant inupstream forest sites, whereas Cordia sinensis, Acacia mellifera, Ziziphusmauritiana and Ficus sycomorus were more common in communities nearer thelake. Older forests generally contained greater diversity of more woodyspecies, greater tree height and truck diameter than downstream leveevegetation, but they did not exhibit clear stratification. Speciespatchiness was broadly characteristic of the riverine zone, particularly themudflats (ancient floodplains) extending away from the fore levees. Firesare frequently set by local inhabitants throughout the grasslands of thelower Omo Basin; within the riverine zone, they are particularly common inthe mudflats but have only limited impact on woodland and forest vegetation.It is suggested that fire is a highly significant factor in theestablishment of sharp boundaries between the closed canopy woodland/forestalong the river and the more xerophytic vegetation of the mudflats.