The effect of Sika deer herbivory on epiphyte diversity changes

Abstract

Habitat changes caused by large deer populations can affect epiphytes on trees through altered microenvironments. We hypothesized that the effect of deer activities on epiphytes differs according to the host tree species and the type of management strategy. To test this hypothesis, the changes in epiphyte diversity were examined on Mt. Odaigahara (Japan), where debarking by Sika deer (Cervus nippon) has caused forests in the eastern part (Picea trees) to decline and the tree trunks have been wrapped with wire mesh to protect them from debarking. In contrast, the forests in the western part (Fagus or Symplocos trees) were less influenced by deer debarking and wire mesh has not been used for protection. A comparison of epiphyte diversity between 1983 and 2008 revealed that the species richness and cover of epiphytes on Picea trees significantly decreased with decreasing dominance of bryophytes with hygrophilous morphological characteristics (hygrophilous life forms). The significant decrease can be explained by both increased drought stress due to tree dieback by deer debarking and metal poisoning from the wire mesh used for tree protection. In contrast, species richness of epiphytes on Fagus trees increased while the cover decreased significantly. These changes may be associated with the drought stress due to the loss of vegetation caused by deer herbivory, which facilitates the new establishment of xerophilous species while decreasing the total epiphyte cover. Unlike epiphytes on Picea and Fagus trees, those on Symplocos trees showed the smallest change between 1983 and 2008. Given that the lowest dominance of hygrophilous life forms was observed on Symplocos trees in 1983, the forest interior could have been drier; hence, drought stress resulting from loss of vegetation by deer herbivory may exert less influence on the epiphytes. Based on these results, the response of epiphytes to deer activities varies according to the host tree species and the presence of protective wire mesh. These differences should be considered when evaluating the influence of deer on epiphyte diversity, and appropriate measures should be implemented for their conservation.