Graduation Date

Summer 2019

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences

Committee Chair Name

Dr. Rosemary Sherriff

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Lucy Kerhoulas

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Jeffrey Kane

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Dr. Harold Zald

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Forestry

Abstract

Oregon white oak (Quercus garryana Douglas ex Hook.) is experiencing increasing competition from Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) across its range at the same time as climate models are predicting increasing climate variability, including drought. Management recommendations that consider competition dynamics between these species under a changing climate are therefore needed for oak woodlands, but we do not currently understand the combined effects of competition, climate, and drought in this ecosystem. This research examines radial tree growth and drought response in Oregon white oak and Douglas fir in an encroached oak woodland near Kneeland, California. Stem maps of local crowding competition were created for 104 Oregon white oak and 104 Douglas-fir trees that were sampled for growth across Douglas-fir encroachment levels. Linear mixed effects models were used to evaluate the effects of DBH, Douglas fir crowding, oak crowding, and climate on tree growth (2002-2016) and drought response (2013-2015). Oregon white oak growth had positive relationships with November-January precipitation, July-August precipitation, April-June mean maximum temperature, and September maximum temperature; and negative relationships with oak crowding, Douglas fir crowding, and summer maximum temperature. Douglas-fir growth had a positive relationship with May-June precipitation and negative relationships with Douglas fir crowding and June-July mean maximum temperature. Oregon white oak growth was more resistant to prolonged drought than Douglas fir. However, oak resistance to drought was also negatively related to Douglas fir crowding and positively related to oak crowding. Oregon white oak may be better suited to a future climate than Douglas fir, but Douglas-fir encroachment will continue to degrade this ecosystem and threaten the ability of Oregon white oak to resist future drought. Prevention and management of Douglas fir encroachment in oak woodlands is therefore encouraged to preserve ecosystem function under climate change.

Citation Style

Forest Science

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