Host-parasite relations of an angiospermous root parasite (Thonningia sanguinea Vahl) in logged and unlogged sites of Budongo forest reserve, western Uganda

摘要

tHost-parasite relationships of an angiospermous root parasite (Thonningia sanguinea) were investigated in logged and unlogged sites of Budongo Forest Reserve. Host trees were identified and their diameters measured in 20 x 20 m plots established randomly in sites where the parasites were presumed to occur. The distance of the point of attachment of the parasite from the base of the host stem was determined and overstorey density measured at the centre of each plot. There were more parasites in the logged than in the unlogged sites (878 and 425 individual parasites ha-1 respectively). The parasite was not host specific but Alchornea laxiflora (Benth) Pax and K.Hoffm, Celtis mildbraedii Engl and Lasiodiscus mildbraedii Engl had relatively more parasites than other species. The parasite could be found within a radius of 2 m from the base of the host stem. The diameter of hosts ranged from 1 to 95 cm. There was a positive correlation between overstorey density and occurrence of T. sanguinea. Conservation of T. sanguinea, therefore, requires maintenance of intact forests with closed canopies rather than logged sites with many gaps and hence low overstorey density. ResumeOn a etudie les relations hote-parasite d'un angiosperme parasite des racines (Thonningia sanguinea) sur des sites exploites ou non de la Reserve forestiere de Budongo. On a identifie les arbres hotes et on a mesure leur diametre dans des parcelles de 20 x 20 m etablies au hasard dans des sites ou le parasite etait suppose se trouver. La distance entre le point d'ancrage du parasite et la base du tronc de l'hote fut determinee, et la densite de la vegetation aerienne fut mesuree au centre de chaque parcelle. Il y avait plus de parasites dans les parcelles exploitees que dans les parcelles nonexploitees (878 et 425 parasites par ha, respectivement). Le parasite n'etait pas specifique de l'hote, mais Alchornea laxiflora (Benth) Pax et K.Hoffm, Celtis mildbraedii Engl et Lasiodiscus mildbraedii Engl avaient relativement plus de parasites que d'autres especes. Le parasite peut se trouver dans un rayon de deux metres de la base du tronc de l'hote. Le diametre du tronc de l'hote variait de 1 a 95 cm. Il y avait une correlation positive entre la densite de la vegetation aerienne et l'occurrence de T. sanguinea. Donc, la conservation de T. sanguinea requiert la preservation de forets intactes avec des canopees fermees plutot que des sites exploites avec des nombreuses clairieres et donc, une faible densite de couverture vegetale.