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Invasive Pine Tree Effects on Northern Coastal Scrub Structure and Composition

Published online by Cambridge University Press:  20 January 2017

Robert J. Steers*
Affiliation:
Inventory & Monitoring Program, San Francisco Area Network, National Park Service, Fort Cronkhite Building 1063, Sausalito, CA 94965
Susan L. Fritzke
Affiliation:
Natural Resources Division, Golden Gate National Recreation Area, National Park Service, Fort Cronkhite Building 1061, Sausalito, CA 94965
Jen J. Rogers
Affiliation:
Inventory & Monitoring Program, San Francisco Area Network, National Park Service, Fort Cronkhite Building 1063, Sausalito, CA 94965
James Cartan
Affiliation:
Inventory & Monitoring Program, San Francisco Area Network, National Park Service, Fort Cronkhite Building 1063, Sausalito, CA 94965
Kaitlyn Hacker
Affiliation:
Inventory & Monitoring Program, San Francisco Area Network, National Park Service, Fort Cronkhite Building 1063, Sausalito, CA 94965
*
Corresponding author's E-mail: robert_steers@nps.gov
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Abstract

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Vegetation that becomes overtopped usually experiences a decrease in abundance or species richness. When an overtopping plant alters the physiognomy of the existing vegetation (e.g., trees invading a shrubland), ecosystem processes can also be dramatically altered. Worldwide, Monterey pine (Pinus radiata) cultivars have been planted in Mediterranean-like climates and are known to invade surrounding natural communities. Ecological impacts resulting from these invasions have been widely investigated; however, the effects from solitary pine trees on the vegetation they overtop are lacking. Furthermore, studies on the impact of P. radiata cultivars from the California floristic province, where P. radiata is native, do not exist. In coastal California, north of the present-day range of native P. radiata stands, cultivars of this species have invaded northern coastal scrub vegetation. To determine the impact of pine invasion on species richness and structure in this habitat, floristic surveys were conducted in 20 blocks that consisted of invaded and uninvaded plots. An invaded plot contained two subplots located under the canopy of an isolated pine tree, whereas a paired, uninvaded plot contained two subplots located in coastal scrub adjacent to each pine. Pine trees selected ranged in size from 2.8 to 119 cm (1.1 to 46.9 in) basal diameter. Our results demonstrate that understory native cover and species richness are negatively correlated with tree size. Understory exotic plant cover and richness of species other than P. radiata did not show any correlation with tree size, mainly because exotic plants had a very low abundance overall.

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Type
Research
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Copyright © Weed Science Society of America