Influences of invasive herb Coreopsis lanceolata on riparian endemic herbs in relation to the understory light availability

摘要

In Japan, invasions of alien herb Coreopsis lanceolata are often observed in riparian endemic vegetation, but the invasion influences on light environments and endemic species are insufficiently evaluated. In this study, we investigated the influences of C. lanceolata and native dominant turf Zoysia japonica on the densities of riparian plants (two endemics Artemisia capillaris and Potentilla chinensis and one alien Lespedeza inschanica) in relation to the understory light availability using 594 0.2 m × 0.2 m plots. Available understory light was influenced negatively by C. lanceolata, not Z. japonica, due probably to the tall stature and dense foliar canopy of C. lanceolata. Understory light availability positively affected densities of riparian endemics, although the relation with L. inschanica was unclear. A. capillaris and P. chinensis densities were negatively related with C. lanceolata, not Z. japonica, implying that C. lanceolata reduces endemic populations. Shading by C. lanceolata would be one of prime factors reducing the endemics. L. inschanica density was not correlated with C. lanceolata cover. C. lanceolata could not shade L. inschanica effectively due to the taller stature of L. inschanica. We considered that C. lanceolata reduces endemic riparian species but coexists with L. inschanica. Preventing invasion and dominance of C. lanceolata is desirable to conserve endemic riparian vegetation.