Abstract
Whitebark pine, a foundation species at tree line in the Western U.S. and Canada, has declined due to native mountain pine beetle epidemics, wildfire, and white pine blister rust. These declines are concerning for the multitude of ecosystem and human benefits provided by this species. An understanding of the climatic correlates associated with spread is needed to successfully manage impacts from forest pathogens. Since 2000 mountain pine beetles have killed 75% of the mature cone-bearing trees in the Greater Yellowstone Ecosystem, and 40.9% of monitored trees have been infected with white pine blister rust. We identified models of white pine blister rust infection which indicated that an August and September interaction between relative humidity and temperature are better predictors of white pine blister rust infection in whitebark pine than location and site characteristics in the Greater Yellowstone Ecosystem. The climate conditions conducive to white pine blister rust occur throughout the ecosystem, but larger trees in relatively warm and humid conditions were more likely to be infected between 2000 and 2018. We mapped the infection probability over the past two decades to identify coarse-scale patterns of climate conditions associated with white pine blister rust infection in whitebark pine.
Highlights
Forest pathogens are a significant contributor to global forest decline [1,2,3] and non-native pathogens can decimate naïve host species, leading to significant disruption in ecosystem structure and function (e.g., Chestnut blight [4])
White pine blister rust in the Greater Yellowstone Ecosystem (GYE) occurs at all elevations and in trees of all sizes, with 40.9% of 5138 trees visited between 2004 and 2018 showing signs of infection
White pine blister rust likely spread from isolated points of white pine blister rust likely spread from isolated points of introduction, we found that introduction, we found that white pine blister rust prevalence in the GYE today is ubiquitous, which white pine blister rust prevalence in the GYE today is ubiquitous, which is not surprising given that is not surprising given that spores can be transported locally within stands and up to 27 km spores can be transported locally within stands are andgenerally up to 27 km favorable under favorable conditions [31]
Summary
Forest pathogens are a significant contributor to global forest decline [1,2,3] and non-native pathogens can decimate naïve host species, leading to significant disruption in ecosystem structure and function (e.g., Chestnut blight [4]). Live plant imports are a major vector for the introduction of many non-native pathogens [5], including white pine blister rust, caused by the fungus Cronartium ribicola. White pine blister rust was introduced to both coasts of North America on European nursery stock in the early 1900s [5,6], and has since become one of the most detrimental exotic pathogens, affecting all species of North American white pines [7,8]. Though not as commercially valuable as other white pine species, whitebark pine (Pinus albicaulis) is a primary contributor to the biodiversity and productivity of high-elevation forests and alpine communities in the interior Pacific Northwest, northern Rocky. In the western U.S, white pine blister rust affects whitebark pine, limber pine (Pinus flexilis), and western white pine (Pinus monticola). White pine blister rust was first observed in the Greater Yellowstone Ecosystem (GYE) in 1937 [10]
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