Protective management of trees against debarking by deer negatively impacts bryophyte diversity

When wildlife populations become too large, they impact other flora and fauna within the ecosystems that they inhabit. For example, the recent rise in population numbers of sika deer in Japan has led to the stripping of bark from tree overstories in forested areas. This has led to protective management actions, such as wrapping the trunks of trees in wire mesh. The present study investigates the impact of this management action on epiphytic diversity at Mt. Ohdaigahara, which is one of the hotspots for bryophyte diversity in Japan. The correlation between the diversity of epiphytic bryophytes and environmental variables was examined, including the presence/absence of wire mesh protection. A generalized linear model showed that species richness and bryophyte cover was significantly correlated with both tree diameter (at 1.5 m height) and tree density (P < 0.01), but negatively correlated with wire mesh protection. Inductively coupled plasma-mass spectrometry analysis showed a significant 3- to 6-fold higher concentration of zinc in bryophytes occupying tree bark under wire mesh protection than for those without wire mesh. Hence, the high sensitivity of bryophytes to zinc accumulation, as a result of toxicity caused by galvanized iron mesh, has led to the loss of species richness and bryophyte cover on tree trunks. Furthermore, other heavy metals found in wire mesh may also contribute to the negative effect on bryophytes. Therefore, to establish best practices for biodiversity conservation that include bryophytes, materials that are free of heavy metals should be preferentially used for tree protection.