A 15-year study on the relationship between beech (Fagus crenata) reproductive-organ production and the numbers of nuisance Japanese black bears (Ursus thibetanus japonicus) killed in a snowy rural region in central Japan

The relationship between beech (Fagus crenata) reproductive-organ (female flowers: FFs, male inflorescences: MIs, and filled masts: FMs) production and the numbers of nuisance Japanese black bears (Ursus thibetanus japonicus) killed (NBs: an indicator of the extent of bear intrusions into residential areas) in a snowy rural region in central Japan was studied over 15 years. The yearly fluctuation of beech reproductive-organ productions between the three study stands was strongly synchronous. There were strong significant pairwise correlations between FFs, MIs and FMs. To identify factors associated with NBs in the May–July (BMJ), August (BA), and September–November (BSN) periods, a model selection procedure using generalized linear mixed effect models was applied with two explanatory variables: FMs in the preceding year (PFMs) and MIs in the current year. Both PFMs and MIs had little effect on BMJ, implying that NBs was independent of these variables in the spring–early summer. MIs had a significant negative effect on BA, implying that NBs increased in mid-summer when MIs were small. PFMs and MIs had significant positive and negative effects, respectively, on BSN, implying that NBs increased in the fall when MIs (i.e., FMs) were small. PFMs had a much smaller effect than did MIs. In conclusion, bear intrusions into human settlements from mid-summer to fall increased in years with minimal MIs, suggesting that bear intrusions in the season of a given year can be predicted by observation of the density of MIs fallen on the forest floor until July in beech stands.