Assessing Growth and Mortality of Bristlecone Pine Infected by Dwarf Mistletoe Using Dendrochronology
2012
Scott, Jared M. | Mathiasen, Robert L.
Bristlecone pine dwarf mistletoe (<named-content content-type="genus-species">Arceuthobium microcarpum</named-content> [Engelm.] Hawksw. & Wiens subsp. <named-content content-type="genus-species">aristatae</named-content> J.M.Scott & Mathiasen) severely parasitizes Rocky Mountain bristlecone pine (<named-content content-type="genus-species">Pinus aristata</named-content> Engelm.) on the San Francisco Peaks, Arizona. We estimated the current incidence of infection and extent of mortality in a mistletoe-infested stand of bristlecone pine on Schultz Peak, a southeast subsidiary ridge of the San Francisco Peaks. Dendrochronological techniques were used to compare radial growth between lightly, moderately, and severely infected and noninfected bristlecone pines. We also paired limber pine (<named-content content-type="genus-species">Pinus flexilis</named-content> James) with noninfected and infected bristlecone pines as another method of estimating the effects of the mistletoe on radial growth. Results suggested that the incidence of infection has increased by approximately 10%, and mortality has increased by approximately 20% since the mid-1970s. Severely infected bristlecone pines had significant growth losses and less annual variation in growth than limber pine or lightly infected and noninfected bristlecone pines. Spatial and temporal trends in mortality of bristlecone pines were measured in two large mortality locations on Schultz Peak. Cross-dating cores from dead bristlecone pines indicated that mortality had rapidly increased starting in 1996. Years of high mortality were related to both high mountain pine beetle (<named-content content-type="genus-species">Dendroctonus ponderosae</named-content> Hopkins) activity and drought conditions.
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