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Limited tree size variation in coastal Oregon, Washington, and British Columbia Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantations makes them susceptible to developing high height to diameter ratios (H/D same units) in the dominant trees. The H/D of a tree is a relative measure of stability under wind and snow loads. Experimental plot data from three large studies was used to evaluate the impact of initial planting densities and thinning on plantation H/D values. The H/D predictions from the experimental plot data match spacing trial results closely but are substantially different than distance-independent growth model predictions. The results suggest that plantation H/D values can be lowered and stability promoted through reduced planting densities or early thinning; however, later thinnings may not be effective in promoting stability, since they do not appear to lower H/D values. Higher initial planting densities shorten the time period during which thinning can be expected to effectively lower future H/D values. Time-sensitive thinning requirements in dense plantations make their management inflexible. The flexibility with which a stand can be managed describes the rigidity of intervention requirements and (or) potential range of stand development pathways.

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A simple stand modcl is developed to assess the influence of management activities in old growth Douglas-fir forests on atmospheric CO, levels. Two natural disturbance regimes (450and 240-year stand replacement fire cycles) are compared with four management regimes (45, 6 5 , 90-year plantation rotations, and conversion to non-forest use). Conversion of old growth Douglas-fir stands to plantations may actually decrease atmospheric C 4 for the fist few decades, but then increase it. The short term and long term changes are negligible compared to the atmospheric C02 produced by burning fossil fuels. Using wood as a substitute product for other materials (brick, aluminum, and plastic) dramatically reduces CO, released to the atmosphere; however, where wood is used as a luxury product, large quantities of C02 are released to the atmosphere under harvest regimes.

Organisms within aquatic and marine environments are subject to a diverse range of often cooccurring abiotic and biotic stressors. These stressors can result from natural phenomena such as native predators and seasonal change in addition to human induced perturbations to natural systems such as climate change and pollution. Despite growing awareness of the complex multistress systems at play in aquatic ecosystems, many questions remain regarding how simultaneous stressors interact with one another and jointly impact aquatic species, particularly when mixing biotic and abiotic stressors or when one of the stressors is an emerging understudied threat like microplastic pollution. We looked at multi-stress interactions in two aquatic study systems to help address this gap in knowledge. In the first, we studied the interaction between ingested microplastics and response to thermal stress in the pacific mole crab (Emerita analoga). We observed a sex specific response where higher microplastic burdens decreased body condition and increased short term thermal tolerance in only female crabs. In the second system, we looked at how diurnal temperature variation, sedimentation, and predator cues altered the movement speed of larval pacific giant salamanders (Dicamptodon tenebrosus), and how simulated low flow summer conditions impact the expression of heat shock proteins (HSPs) in the same species. Larvae moved faster in the presence of chemical cues from trout and suspended sediment but were only marginally affected by temperature and unaffected by visual cues from conspecifics. Additionally, larvae exposed to low flow conditions had more variable, but not significantly higher, expression of HSPs. Looking at these types of multi-stress systems and their effects is important for understanding the full effects of co-occurring stressors on aquatic and marine organisms to guide appropriate conservation and management responses. v Acknowledgements I would like to acknowledge my funding sources the Genentech foundation and the ARCS foundation, as well as Jeremiah Ets-Hokin and Loni Matthew from the Stillman lab, Conor Harrington, Bria Boose, and Max Taus from the Vredenburg lab, Raquel Reyes from the Chaves lab, and Shannon Summers from the Swei lab, all of whom assisted me greatly in this endeavor. I also would like to acknowledge Dr. Annette Chan from the CMIC and Dr. Colleen Ingram from the GTAC at San Francisco State University for their assistance and teaching. Finally, I would like to acknowledge Ed Reyes for his assistance with builds associated with this project. vi Table of Contents List of Figures Introduction Organisms in aquatic and marine environments around the world are experiencing multiple co -occurring stressors resulting from natural phenomena and anthropogenic impacts [1, 2]. These stressors can be either biotic (e.g., predation [3], competition [4]) or abiotic (e.g., temperature, pH, salinity [1, 2]). Many of these stressors are worsening due to changes at global scales such as climate change [5], plastic pol...