Habitat traits of Polygala reinii in secondary Pinus densiflora-Quercus serrata forests of the southeastern parts of the Hyogo Prefecture

Abstract

Polygala reinii Franch. et Sav. is a perennial herb endemic to the Kinki and Tokai districts of Japan.　To clarify the habitat traits of P. reinii, we surveyed the distribution area of this species and compared the environmental conditions, stand structure, life-form spectra, and floristic composition between the habitats and the non-habitats in secondary Pinus densiflora-Quercus serrata forests of the southeastern parts of the Hyogo Prefecture. Additionally, we examined the relationship between the environmental conditions and the density of P. reinii individuals within the study area and assessed the variation in climatic conditions and habitats in the entire geographical distribution range of P. reinii by inspecting their specimens stored in several herbaria.　The results of the field survey showed that P. reinii was found mostly on the crest slopes along ridge lines.　In the habitats, the organic layer was thinner, the electric conductivity of surface soil was lower, and the soil hardness was greater, compared to those in the non-habitats.　Evergreen broad-leaved trees were commonly dominant in the understory of both, the habitats and the non-habitats.　Meanwhile, deciduous broad-leaved trees were more abundant in the understory of the habitats than in that of the non-habitats.　Life-form spectra and floristic composition were characterized by a higher proportion of perennial herbs, including forest edge species and grassland species.　The density of the P. reinii individuals was positively correlated with overstory opening and soil hardness while being negatively correlated with the thickness of the organic layer.　These results suggested that the undeveloped forests such as open forests are suitable habitats for the growth and establishment of P. reinii. This was also supported by the habitat records found on the labels of several specimens of this species.　Selective cutting of inhibitors such as the evergreen broad-leaved trees is thus considered to be necessary for the conservation of P. reinii.　This is especially important in the stands where they are growing dominant with the progression of vegetation succession after the cessation of traditional management．