"Escape of Introduced Ornamentals in Asteraceae" : with main focus on Tagetes patula L. in Western Ethiopia

Abstract

Introduced plant species may lead to negative consequences for the local community by outcompeting other species, and in extreme situations decrease biodiversity. It is well known that once an invasive species becomes firmly established, its control might be difficult and eradication may be more or less impossible. Benshangul Gumuz National Regional State in Western Ethiopia inhabits several endemics, and is not very well studied, so far. Features of Tagetes patula and Zinnia elegans, two introduced ornamentals that has escaped cultivation in the area, will in this thesis be studied. The endemic species Bidens prestinaria will be used in some of the experiments for comparison. People in Western Ethiopia are dependent on their crops. An increasing growth of the already naturalized ornamentals might have negative consequences in this regard. Successful invasion is associated by characteristics as (among others), a large seed production, a soil seed bank, a rapid growth rate, and a stimulated growth of side shoots after grazing/trampling. Tagetes patula possess all these characteristics. Zinnia elegans was not found escaped to the same degree as Tagetes patula, and was accordingly regarded not to be as potentially invasive as T. patula. A species association analysis revealed that Tagetes patula was mainly found in the association characterised by tree species, and the association was also containing species demanding some shade and moisture. It was less frequently found in associations were the species composition represented open and more arid habitat types. Bidens prestinaria, however, preferred both associations. To study if fire could be a way to control the species, diaspores of T. patula and Z. elegans were exposed to different fire simulation treatments. Surprisingly, the result suggested that diaspores of the two ornamental species, to a certain degree will withstand fire, unless the heat becomes excessive. The near endemic species Bidens prestinaria was apparently not affected by the heat treatments.