Abstract
The soil seedbank of Tithonia diversifolia, an invasive species which dominates open waste fallowland vegetation was studied. Two different roadside sites which vary in extent of open waste land were selected.The species composition of the established vegetation was assessed in the two diferent sites. Twenty top soil samples were collected at five different distances (15 cm, 30 cm, 45 cm, 60 cm, and 75 cm) inwards away from each main road in dry and rainy seasons and the seed bank composition was determined by greenhouse germination over a 6 month period. The similarity between the composition of the seed bank flora and that of the established vegetation was low. The least and the highest emerged seedlings density was recorded in the 15 metres and 75 metres respectively inwards away from the main road in both seasons. The results of the seedlings emergence is a reflection of the extent of open waste land dominated by the invasive species due to human disturbance (road construction) on both sites. Overall results suggest that the emergence of the species from the soil seed bank may be due to the impact of the invasive species Tithonia diversifolia on other plant species in the study environment.
Highlights
The introduction of plant species into a new environment, deliberately or otherwise, can have many unanticipated ecological effects (Howard and Harteminkl, 2000).These introduced species, otherwise called invasive species, can have devastating effects on the ecosystem quality and functioning as they often time out-compete indigenous or native species, thereby leading to the extinction or disappearance of endemic species (Lorence and Suesman, 1986)
The standing vegetation species composition of the two study sites is presented in Tab. 1
Thirty-two (32) plant species belonging to 22 families were encountered in the standing vegetation in the two sites; the species were predominantly shrubs and herbaceous species
Summary
The introduction of plant species into a new environment, deliberately or otherwise, can have many unanticipated ecological effects (Howard and Harteminkl, 2000). These introduced species, otherwise called invasive species, can have devastating effects on the ecosystem quality and functioning as they often time out-compete indigenous or native species, thereby leading to the extinction or disappearance of endemic species (Lorence and Suesman, 1986). The mechanism by which invasive species affect native communities may include competition, altered ecosystem processes, or other pathways like allelopathy or phytotoxicity (Samuel et al, 2005). Invasive species have been reported to affect seedlings emergence of native species to varying degrees (Samuel et al, 2005)
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