Warren D. Devine, Constance A. Harrington

In the Willamette Valley area of the Cascade mountain range in the Pacific Northwest region of the United States there have been high levels of encroachment of Douglas-fir (Pseudotsuga menziesii) on Oregon white oak (Quercus garryana). These savanna and woodland areas were historically kept-up by frequent burns, usually caused by humans for many reasons. Oaks typically need direct sunlight to photosynthesize, so encroachment of Douglas-firs that have been overtopping oaks has caused oaks to live in suppression for decades, which hinders biodiversity, lifespan of the oaks, and the amount of acorns they produce. This study looks at how oaks respond over ten years to the invasion of Douglas-firs being removed. There were four different methods of release measured: Full release, or full removal of douglas firs in a plot, half release, thin only, and control in which there was no removal. Growth of oaks in plots where full removal of Douglas-firs was done was significantly greater than in plots where other treatments were done. Acorn production was also handily influenced by full removal of Douglas-firs, however, height and crown area growth was not influenced. Acorn production in thinned and half released plots also improved, but not as high as full release areas. Treatments indicated that removal of encroaching fir trees highly influenced oaks to grow rapidly and oaks showed no negative effects due to a dramatic change in environment.

Data needed for this study was behavioral because the forest ecologists were determining how oaks responded in growth to a change in surroundings. This is simply observing the tree’s behavior, but can be confusing because you are not testing human subjects. Data was collected by measuring plots that had 18 oak trees each with a wide range of DBH (diameter at breast height) with varying degrees of suppression. Data was analysed by a generalized, randomized, complete-block design analysis of variance (ANOVA) model. The experimental unit was the center oak of the plot.

Devine, W. D., & Harrington, C. A. (2013). Restoration release of overtopped Oregon white oak increases 10-year growth and acorn production. Forest Ecology & Management, 29187-95. doi:10.1016/j.foreco.2012.10.053