Spatial and Climate Analysis of Bigleaf Maple Decline in Western Washington Rachel DeCordoba Background Spatial Results Adviser: Dr. Patrick Tobin Climate Results Bigleaf maple trees (Acer macrophyllum) are an iconic species in Western Washington, but starting around 2010, they have undergone significant dieback, marked by tree mortality, reduced/yellowing leaf growth, and crown thinning. The Washington State Department of Natural Resources (DNR) has examined the presence of Verticillium wilt, Xylella fastidiosa bacteria, Phytophthera (a root pathogen), and Armillaria (a parasitic fungi) as possible causes of symptoms and mortality, determining that none of the pathogens were significantly present in all symptomatic trees. In 2014, WA DNR sampled 56 affected sites, recording symptoms of both individual trees and stands. Temperature trends varied seasonally for all three cities, as predicted. Precipitation varied as well, with more deviation overall. The most significant increases in precipitation occurred in Centralia and Portland, the two cities nearest to sites showing smaller percentages in mortality. The years preceding the first reports of Bigleaf maple decline (2010) show periods of both drought and above average precipitation. A healthy Acer macrophyllum leaf (left) compared to one with significantly stunted growth (right) A sampled tree showing symptoms of crown dieback. Methods Two sets of data were collected and analyzed for this project. The first set consisted of National Oceanic and Atmospheric Administration (NOAA) temperature and precipitation data during 2000-2015 from three cities throughout the general area of DNR sample sites: Everett, WA, Centralia, WA, and Portland, OR. Any especially unusual or severe trends may indicate climate reasons for tree stress and subsequent decline. Discussion Trees with larger DBHs were assumed to be older in age. Tree ages were fairly diverse amongst the site samples, with a slightly greater population of younger trees than older trees (A). Individual trees exhibited a wide range of severity in crown dieback, with some trees showing an unaffected crown and others in severe decline (B). Stands surrounding sample trees exhibited a wide range of crown thinning as well, with higher likelihood of severe thinning as opposed to mild (C). Stands surrounding sample trees exhibited low levels of mortality overall, usually between 0-10% (D). Acknowledgements Many thanks to my adviser Dr. Patrick Tobin for his help with guiding the project, introducing me to the wonders of R for spatial analysis (and other functions), and mentoring me throughout the process. Thank you to graduate student Riley Metz for her help with ArcMap and organizing data to be used between programs. Thank you to Amy Ramsey and her team at the Washington State Department of Natural Resources for providing background information about Bigleaf maple decline, data from multiple symptomatic tree surveys, and information about previous studies. The second consisted of analyzing WA DNR symptomatic tree and stand data, based upon the parameters of stunted leaf growth, mortality, crown thinning, and diameter at breast height (DBH). Locations of all 56 trees were plotted in ArcMap and spatially analyzed using the program R. Spatially significant clusters of affected trees could indicate pathogen or other biotic influence. Looking specifically at the variables of stand mortality and stand reduced leaf size, there is very little spatial correlation between location and each variable’s intensity, especially as distance betweens sites increases (left). Using Ripley’s L function to look for deviations from spatial clustering, the spacing of all 56 sample trees was found to be significantly clustered, as noted by the solid black, which is outside of the expectation under complete spatial randomness (grey area) (right). A map showing locations of the 56 tree sites surveyed by The Washington State Department of Natural Resources in 2014, with red indicating higher levels of stand mortality. The three cities from which climate data was obtained are denoted as well. This study found that climate patterns do not appear to have an effect on tree death, although analysis with R found that symptomatic trees are significantly spatially clustered. There is a significant correlation between mortality and reduced leaf size with location, but no significance with regards to symptom intensity. The spatial clustering of affected trees indicates that the cause of decline could still be a biotic factor, though further specific studies will be necessary in order to determine which pathogen, if any, is responsible for widespread symptoms. •Big Leaf Maple Tree Data. 2014. Raw data. Washington DNR. •National Oceanic and Atmospheric Administration, National Centers for Environmental Information. Climate Data: Monthly Totals. 2016. Raw data. •Ramsey, Amy. Crown dieback in bigleaf maple sampled for Verticillium wilt. Digital image. Washington State Department of Natural Resources. Mar. 2012. Web. •Ramsey, Amy. Healthy (1) vs. symptomatic (2) bigleaf maple leaves. Digital image. Washington State Department of Natural Resources. Mar. 2012. Web.