Spiral grain in bristlecone pines (Pinus longaeva) exhibits no correlation with environmental factors
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Six hundred and eleven Great Basin bristlecone pines (Pinus longaeva) were surveyed in two separate groves in California’s White Mountains. The presence and direction of spiral grain were recorded for each tree as well as elevation above sea level, horizon angles, latitude and longitude, trunk diameter, whether the tree was dead, and whether the trunk was broken. The proportions of left-handed, right-handed and straight trees were similar in every part of both groves, although the groves lie at different elevations. No significant correlation was found between the direction of spiral grain and any environmental factor. The hypothesis that spiral grain is an adaptation to distribute sap evenly between the roots and the crown in Pinus longaeva is not strongly supported, since spiral grain is not correlated with asymmetric environments and most trees exhibit <90° rotation through the main stem. The data also do not support the idea that spiral grain makes the tree more resistant to breaking in strong winds. Right-handed spiral grain is predicted by this hypothesis, but most bristlecone pines are either left-handed or exhibit no spiral grain. Bristlecone pines are often uprooted from thin soils by strong winds, but rarely are the main stems broken by this mechanism. Spiral grain in Pinus longaeva growing in California’s White Mountains does not appear to be under environmental control.
KeywordsSpiral grain Bristlecone pine Wind torque Supply hypothesis Left-handed Right-handed
The authors thank the staff of the University of California’s White Mountain Research Center for hosting our stays in the field. This project was made possible by financial support from the Drake Fund. We thank the many volunteers who participated in this project, including Olivia Ashmoore, Mary Buchanan, Cooper Clark, Dorcy Brownback Curth, Sandy Curth, Jordan Doering, Brennan Duff, Greg Gabel, Matthew Gabel, Murphy Goodwin, John Hayden, Cole Hersey, Daniel Hunt, Sophia Lahey, George Lightfoot, Lori Martz, Rich Melbostad, Emma Mooney, Anthony Scopazzi, Jonathan Scopazzi, Jonathan Sicroff, Olivia Sicroff, Jack Sims, Abby Smith, and Cesi Solari. We thank Michelle Lackney for guidance on the use of statistics.
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