Overgrowth of the hemiparasitic plant species Taxillus yadoriki （Loranthaceae） and the debilitation of its host trees in a park in Miyazaki City, Miyazaki Prefecture

Abstract

Taxillus yadoriki （Loranthaceae） is a hemiparasitic plant species that attaches to the stems and branches of trees. There are many host trees of T. yadoriki in a park in Miyazaki City, Miyazaki Prefecture. In this park, we surveyed the species, size, and degree of debilitation of these host trees and the foliar cover of T. yadoriki in order to examine the host specificity of T. yadoriki and the effects of its parasitism on trees. In addition, we resurveyed the degree of debilitation after 4 to 5 years. A total of 422 host trees from 27 species were observed in the park. This study and a literature survey revealed that there were at least 67 species （29 families） of the host trees of T. yadoriki in Japan. Lithocarpus edulis was the most common host tree, comprising 62.9% of all host trees. The frequency that L. edulis trees were infected by T. yadoriki was higher in taller trees and canopy trees. An analysis of host specificity using Jacob’s selectivity index suggested that T. yadoriki had a preference for the tree species L. edulis, Quercus serrata, Cryptomeria japonica, and Eurya japonica var. japonica. The degree of debilitation of the host trees was graded on a scale of one to five. Most host trees （86.7%） were debilitated, and the debilitation grade for L. edulis had a highly positive correlation with the foliar cover of T. yadoriki. Therefore, it was determined that T. yadoriki induced the tree debilitation. A resurvey indicated that T. yadoriki killed host trees and that L. edulis was susceptible to death by parasitism.