NATURAL HISTORY AND DEMOGRAPHY OF THE IMPERILED REDWOOD FOREST SPECIALIST PEDICULARIS DUDLEYI (DUDLEY'S LOUSEWORT, OROBANCHACEAE)

Abstract

Dudley's Lousewort (Pedicularis dudleyi Elmer) is a rare and apparently declining species confined to two populations associated with Redwood forests in coastal California. In this study, we aimed to determine whether pollination, seed dispersal, or seed germination were important limiting factors for population growth of P. dudleyi at Portola Redwoods State Park, the northernmost of the two known populations. We conducted a full census of the population, performed pollinator and seed disperser observations, conducted a pollinator exclusion study, and conducted a litter removal experiment and a greenhouse seed germination study. Fewer than 500 reproductive individuals were found in the census, confirming the extremely small population size at the State Park. Both pollination by native bees (Bombus spp. Latreille 1802) and seed dispersal by yellowjackets (Vespula alascensis Packard 1870) appear to be robust. The litter removal results were inconclusive and no seeds successfully germinated. Combining age class data from the census, poor overall recruitment in the litter removal trial, and poor seed germination, we infer that low establishment of new individuals and populations is a primary threat to the species and should be the focus of future management goals.