The Effects of Canopy Structure on the Distribution of Mistletoe (Viscum album L. subsp. coloratum Kom.) in a Deciduous Forest

Abstract

We examined the effect of canopy structure on the distribution of mistletoe (Viscum album L. subsp. coloratum Kom), an arboreal hemiparasite, in deciduous forests. We recorded the existence of V. album on every tree (diameter at breast height >= 20cm) in a deciduous forest (170 × 190 m plot). We used tree position, crown projection area, tree height, treetop elevation (tree height + elevation above sea level), and number of trees within a given radius as indices of isolation and protrusion for each tree. We performed a logistic regression analysis based on a generalized linear mixed model to elucidate the relation between the number of trees in the vicinity of each tree and the distribution of V. album. A greater number of trees surrounding a tree had a significantly negative effect on the likelihood of finding V. album on that tree. When counting the number of a tree in the vicinity of a tree, counting only trees with higher treetop elevations than the tree being analyzed led to a more valid model than including all trees around it. The isolation and protrusion of tree crown must be important factors determining the distribution of V. album in a deciduous forest, suggesting that presence of V. album is related to the canopy dynamics.