Seedling population size and microhabitat association in Lupinus oreganus A. Heller var. kincaidii C.P. Sm. (Fabaceae) a threatened plant of western Oregon grasslands

Abstract

Lupinus oreganus A. Heller var. kincaidii C.P. Sm. (Fabaceae) is a federally listed Threatened, endemic, perennial species of western Oregon grasslands and is the primary host plant for the Endangered Fender’s blue butterfly (Plebejus icarioides fenderi Macy [Lepidoptera: Lycaenidae]). For effective conservation and restoration, determining the habitat characteristics that are related to natural seed germination is necessary, yet unknown, for Kincaid’s lupine. In 6 populations of Kincaid’s lupine, generally < 1% of the estimated seed cohort became seedlings the following year, and pre-dispersal seed predation by weevil (Tychius lineellus Le Conte [Coleoptera: Curculionidae]) larvae can substantially reduce the estimated seedling population size. The likelihood of seedling presence increased with a decreasing amount of thatch but no relationship between lupine plant density and seedling likelihood was detected. Kincaid’s lupine seedlings were found in habitats with ample exposure to light, such as beds of moss and in areas of grass < 10 cm (4 in) tall. Land managers may encourage larger germinant populations of Kincaid’s lupine by decreasing the amount of thatch; controlling the abundance of exotic, rhizomatous grasses; and targeting habitats with short-stature bunch grasses for restoration (seed sowing).