Taxus brevifolia Nutt., commonly known as Pacific or Western yew, is a conifer native to the Pacific Northwest of North America. Contrary to other Taxus species, T. brevifolia staminate strobili are usually located on two-year old foliage though they may occur on foliage from one to five years old. This delayed staminate strobilus development may be an adaptation to the low light environment where T. brevifolia grows. Microsporogenesis was found to occur in the fall preceding pollination. Isobilateral tetrads were visible as early as mid-October. Over-wintering staminate strobili usually contained separate microspores. In 1996 through 1999, pollination occurred in March and April in two natural forest sites on southern Vancouver Island, British Columbia. Low amounts of airborne pollen and a prolonged pollination period indicated low pollination success within T. brevifolia. Female receptivity was measured by the presence of a pollination drop and protandry up to 18 days was observed. In vitro pollen germination was moderate to good, ranging from 65% to 88%. DAPI fluorescence staining showed successful male gametophyte development in vitro. The phenology of megasporogenesis and free nuclear mitosis within the megagametophyte was variable and this development occurred anytime between early February until the end of June. One megaspore mother cell developed from the sporogenous tissue and underwent meiosis forming a linear tetrad of megaspores. Though up to three of the megaspores may be functional, the chalazal megaspore developed faster than the others and became the dominant megaspore. Cellularization of the megagametophyte began in mid-April and continues until early June. The presence of an ephemeral ventral canal nucleus was confirmed. Fertilization was observed in June in 1996. The mature egg cell cytoplasm and sperm structure was used to infer paternal inheritance of plastids and biparental inheritance of mitochondria. To examine this further, DNA was extracted from hybrid embryos of T. brevifolia and T. x media Rehd. Paternal contribution of mitochondria was confirmed using the probe rpS 14-cob. The T. x media parents produced two bands of 526 and 970 by in length, whereas the T. brevifolia parents produced only one band (526 bp). The chloroplast probes were not effective at amplifying Taxus DNA although appropriate sized bands were produced in Pinus contorta. Proembryos occurred from mid-May to mid-June. Sixteen nuclei were present before cellularization. Early embryos were present from mid-May to mid-August. Simple polyembryony was observed up to the massive embryo stage and differential growth of the embryonal cells was interpreted as incomplete cleavage polyembryony. Mid-embryos were present from mid-June to late August and had a distinct protoderm and focal zone. Late embryos were visible from mid-July onwards. Starch began accumulating at the early embryo stage, whereas, proteins and lipids accumulated in the late embryo stage. The presence of a red aril corresponded to increased amounts of lipid in the megagametophyte cells. Individual seeds matured from July until November. The seed efficiency ranged from 0% to 16% and averaged 5%. Pre-zygotic loss was the most common fate of ovules, followed by post-zygotic loss. Possible causes of this poor seed efficiency are poor pollination success, insect damage or light limitation. / Graduate

In 1991 Pacific yew (Taxus brevifolia Nutt.) was reported as a new host for Phytophthora lateralis Tucker and Milbrath which is an aggressive root rot pathogen thought previously to be specific to Port-Orford-cedar. This study was designed to compare the pathogenicity of P. lateralis on the two hosts, and to characterize sites where Pacific yew mortality occurs. The specific objectives were: 1) compare root colonization and mortality of Pacific yew and Port-Orford-cedar seedlings and rooted cuttings; 2) compare lesion length on inoculated Pacific yew and Port-Orford-cedar branches and stems; 3) compare zoospore attraction to freshly cut Pacific yew and Port-Orford-cedar rootlets; 4) compare amount of mortality of Pacific yew and Port-Orford-cedar in infested drainages and determine extent of yew mortality; and 5) characterize sites where P. lateralis causes Pacific yew mortality. Root colonization of P. lateralis was significantly greater in cedar than in yew. Seedling mortality averaged 58% for cedar and 4% for yew. Lesion length on the cedar seedling stems was twice the lesion length on yew stems, and cedar branches had lesions four times longer than yew branches. Abundant zoospore aggregation occurred on cedar rootlets along the zone of elongation and the region of maturation. In comparison, far fewer zoospores encysted along the yew rootlets, and were concentrated on the root hairs. The stream survey of three infested drainages in southwest Oregon and northwest California revealed a total of 1199 dead Port-Orford-cedar (46% mortality), and 86 dead Pacific yew (10% mortality). At sites where P. lateralis-induced mortality occurred, the interaction of slope and distance from the stream was negatively correlated with tree death. Based on results of this study, we conclude that Pacific yew is less susceptible to P. lateralis than Port-Orford-cedar, but that mortality of Pacific yew in the field is greater than previously reported. In addition, Pacific yew mortality was observed most often on level to nearly-level sites close to the stream's edge where root exposure to P. lateralis-infested water was frequent in scope and duration. / Graduation date: 1995

Indigenous landscape management has transformed ecosystems for millennia, with long-lasting impacts on the productivity and abundance of plant species. While western science based ecological research is beginning to investigate these impacts, less abundant species of cultural importance remain understudied. Pacific yew (Taxus brevifolia Nutt.), an uncommon understory conifer found in old-growth forests of the Northwest Coast of North America, has not received sustained ecological interest despite its importance to Indigenous Peoples throughout its range. In the first chapter, I synthesize the current ethnobotanical and ecological literature discussing Pacific yew to identify knowledge gaps and dominant paradigms that have shaped the study of the species. I find that many mechanisms behind Pacific yew’s habitat selection and ecosystem functions are unknown to western science and that the impacts of Indigenous landscape management are largely unacknowledged within the western scientific literature. In the following chapter, in partnership with the Heiltsuk First Nation, I examine the growth and abundance of Pacific yew on sites that were inhabited intensively by First Nations on the Central Coast of British Columbia for over 10,000 years. I find that habitation histories are not a strong driver of patterns of tree size and that Pacific yew abundance is largely driven by site aspect. These findings shed light on the habitat preferences of Pacific yew, which have rarely been studied in this region. They also illustrate variation in the response of culturally important species to landscape modification and highlight the need for nuanced understanding of the diversity of plant management strategies employed by Indigenous Peoples. This work is part of a broader attempt to incorporate cultural histories and questions into ecological study and to recognize the continuing ecological influences of Indigenous Peoples, who have stewarded their homelands for millennia. / Graduate