Is Sweetgrass on the Decline? Response of Schoenoplectus pungens (M. Vahl) Palla var. badius (K. Presl) S. G. Smith to Environmental Variables, Cultural Use, and Anthropogenic Change in Grays Harbor, Washington

Abstract

University of Washington Abstract Is Sweetgrass on the Decline? Response of Schoenoplectus pungens (M. Vahl) Palla var. badius (K. Presl) S. G. Smith to Environmental Variables, Cultural Use, and Anthropogenic Change in Grays Harbor, Washington Caren Jane Crandell Chair of the Supervisory Committee: Kern Ewing School of Environmental and Forest Sciences The bulrush Schoenoplectus pungens is native to the brackish marshes of the Pacific Northwest and is used by Native Americans in basketry. Called sweetgrass by local weavers, the clonal species dominates portions of Grays Harbor National Wildlife Refuge in Washington and displays enormous variation across the landscape and sometimes within the space of a few centimeters. The refuge has become the region’s primary gathering ground for sweetgrass, but in the last two decades, weavers have become concerned about the quality of the material they collect. In the first chapter I explore the environmental variables that contribute to the variation in S. pungens characteristics. Data was collected along ten transects and analyzed using principal components analysis and multiple regression with a Specified Analysis Plan to minimize Type I error. Maximum stem height was more responsive to the measured variables than other plant attributes and was positively associated with percent sand, percent moisture, and sulfide, when confounding factors were accounted for. It was negatively associated with elevation (inundation class), salinity, percent macro-organic matter (MOM), and redox potential. Stem density was positively associated with elevation (inundation class), percent sand, and moisture, when confounding factors were accounted for. Stem density was negatively associated with percent MOM. Stem caliber was negatively associated with elevation (inundation class). Aboveground (AG) biomass was positively associated with elevation (inundation class), percent sand, and moisture when confounding factors were accounted for. The elevation optimum appeared to shift from a higher to a lower elevation zone between 1999 and 2006, possibly as a result of sedimentation that “raised the floor” of the marsh. In the second chapter, I report the results of an in situ multi-year randomized block experiment conducted at four sites to determine what harvest regime(s) may be sustainable for sweetgrass. Two intensities (100% and 25% stem harvest) and two frequencies (one and two consecutive years of harvest) were tested, including a year of rest following one year of harvest. Our results lead us to conclude that a) at least one year of rest after harvest is important for the plant’s recovery; b) selective harvest of 25 percent of stems in a patch, with at least one year of rest following harvest, does not appear to have a negative impact on plant attributes; and c) stems over 130 cm may not be affected by harvest. Finally, I examine the environmental history and cultural geography of sweetgrass in Grays Harbor. I propose that the plant migrated along the shoreline in response to anthropogenic change and the weavers followed, adapting to changing conditions as they have for millennia. I also address factors in surrounding watersheds that contributed to a convergence of harvesting on the shores of the wildlife refuge. To account for these adaptive shifts and ensure access of Native American weavers to this important cultural resource, I suggest that, as time passes, gathering grounds be understood functionally rather than strictly geographically.