Graduation Date

Fall 2017

Document Type

Thesis

Program

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

Committee Chair Name

Andrew Stubblefield

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Lucy Kerhoulas

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Rosemary Sherriff

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Watershed Management

Abstract

The Pacific Northwest region is predicted to encounter rising temperatures over the next century, ultimately leading to less water storage during seasonal drought periods. Vast coniferous forests dependent upon this storage and will encounter periods of increased stress due to the lessening of available water supply. Under these conditions, stream flows will be directly affected by the forests competing for freshwater sources. Thinning treatments have been investigated as a means to compensate for increased water use by even-aged forest stands left over from past logging-practices.

This study was completed on two sites within Humboldt County, CA: one inland site with a relatively dry climate and one coastal site with a wetter climate. Thinning treatments were implemented at the dry site in fall of 2014, while the wet site underwent thinning treatments in 2009. For this study, eight sample Douglas-fir trees were chosen at each site representing various sizes and levels of competition. Sap flow measurements were taken during the summer drought period in 2015 and 2016. Water use was compared between trees, sites, and sample periods, with a focus on the differences between 2015, the fourth year in a 4-year drought, and 2016, an exceptionally wet year. Patterns of water use were strongly affected by the drought, manifested as high nighttime water use due to cavitation and increased dependency on bole water storage. Adaptive water use strategies of the old-growth sample tree (diameter at breast height (DBH) = 104 cm) and increased water allocated to sample trees receiving more solar radiation were observed as well. Despite an above average annual precipitation in 2016, increased water stress was evident at the dry site, likely due to understory regeneration following thinning treatments and increased growth characteristic of a re-watering year. DBH was positively correlated with water use during the lower stress 2016 growing season, while poorly correlated during preceding season of high stress, signifying that other factors may play a more important role when assessing water use during times of low water availability. Local competition was not found to significantly influence tree water use.

Citation Style

APA

Included in

Hydrology Commons

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