Survival of the rare Packera layneae (Asteraceae), under chaparral and after fire

Abstract

Conservation of rare plants requires an understanding of how the species responds to natural and artificial disturbance dynamics. For chaparral species this includes the natural disturbances of fire and shrub canopy closure during the interfire period, and the effect of shrub clearing for fuel reduction. Packera layneae is a federally listed rare herbaceous perennial subject to all these disturbances; its center of distribution is upon the gabbro soils surrounding Pine Hill in western El Dorado County, CA an area known as a hotspot of botanical diversity. Combining genetic data with mapping following a 2007 wildfire in Shingle Springs, we found that the species survives fire and chaparral overgrowth due to underground rhizomes and caudices that resprout after fire and enable its persistence under dense chaparral canopies; as well, seed recruitment of new genetic individuals occurred within discrete patches. Seedlings were not found the spring following the 2007 fire, suggesting fire killed the soft-walled seeds. Surveys across the Pine Hill area from 2005-2007 found populations flowering and producing seed in recently burned and cleared areas as well as under mature chaparral; however, the proportion of plants flowering decreased as shrub density increased. From our 2019 surveys of a new 4.25 km fuel break around the perimeter of Pine Hill in Rescue, CA (0.983 km2) we found the species resprouted from plants growing under the dense chaparral canopy on the southern, eastern, and western aspects but did not occur on the northern exposure or under dense oak canopy. As the seedling regeneration niche is unknown, preservation of established populations is vital to the long-term persistence of the species.