Regeneration and expansion of Quercus tomentella (island oak) groves on Santa Rosa Island

Western North American Naturalist
By: , and 

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Abstract

Quercus tomentella (island oak) is an endemic species that plays a key functional role in Channel Island ecosystems. Growing in groves on highland ridges, Q. tomentella captures fog and increases water inputs, stabilizes soils, and provides habitat for flora and fauna. This cloud forest system has been impacted by a long history of ranching, and restoration efforts are underway that include erosion control, leaf litter capture, fog capture, and reforestation. To inform retoration efforts, we explored tree regeneration and the potential for Q. tomentella grove expansion on Santa Rosa Island. We delineated current and historic groves at Black Mountain by comparing stand maps from 1989 and aerial photographs from 1994 and 2015. We evaluated regeneration in the outlying areas by recording the location, diameter at breast height, number of trunks, height class, percent crown mortality, nurse plant species (if present), and reproductive status for all 4355 outlying seedlings, saplings, and mature trees. We defined outliers as individuals that were 15 m outside of the canopy of island oak groves. There are 14 groves at Black Mountain, and grove size expanded by an average of 36.9% (SD 18.5%) between 1994 and 2015. Nurse plants correlated positively with outlier tree height and reduced percent crown mortality. This effect is potentially due to increased fog drip from nurse plant species such as Quercus pacifica (island scrub oak), Heteromeles arbutifolia (toyon), and Baccharis pilularis (coyote brush). These results indicate that Q. tomentella is regenerating and that nurse plants can serve as catalysts for ecosystem restoration.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Regeneration and expansion of Quercus tomentella (island oak) groves on Santa Rosa Island
Series title Western North American Naturalist
DOI 10.3398/064.078.0415
Volume 78
Issue 4
Year Published 2018
Language English
Publisher Monte L. Bean Life Science Museum (Brigham Young University)
Contributing office(s) Western Ecological Research Center
Description 10 p.
First page 758
Last page 767
Country United States
State California
Other Geospatial Santa Rosa Island