Document Type


Date of Degree Completion

Summer 2015

Degree Name

Master of Science (MS)



Committee Chair

Mary E. Poulson

Second Committee Member

Raymon Donahue

Third Committee Member

Tom Cottrell


The purpose of this study was to determine physiological differences in drought response among Garry oak (Quercus garryana Douglas ex Hook. [Fagaceae]) seedlings that grow in distinct populations in Washington state, in order to aid in restoration efforts by informing growers of the potential differences between the acorn collection sites. Acorns from six Washington populations east of the Cascades, as well as one population from Whidbey Island, were collected and grown in containers under controlled conditions. The plants were assessed with and without moderate and severe drought stress induced by withholding water. The most extreme differences in photosynthetic characteristics for non-stressed seedlings from different populations were in stomatal conductance rates, which in some cases differed between populations by 2 fold or more. Differences in response to drought occurred across populations after 14 days of withholding water (Fig 4). Seedlings from the northernmost population of Garry oak on the east side of the Cascades (Swauk Creek) were most susceptible to lowered photosynthetic rates induced by drought stress, while an island population from the west side of the cascades (Oak Harbor) showed the least drought-induced reduction of assimilation. Differences among populations were also observed in the occurrence of drought induced embolisms, and in changes in leaf water potential, relative water content, and production of the osmolyte proline in response to drought. This study shows that seedlings from different populations of Garry oak have distinct physiological responses to drought that may lead to changes in survivorship for seedlings used in reforestation efforts for Garry oak savannas as they are exposed to drought stress in the field.