Evidence of Tree Species’ Range Shifts in a Complex Landscape

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The article was published by the Public Library of Science and is in the public domain. The published article can be found at: http://www.plosone.org/.Climate change is expected to change the distribution of species. For long-lived, sessile\ud species such as trees, tracking the warming climate depends on seedling colonization of\ud newly favorable areas. We compare the distribution of seedlings and mature trees for all but\ud the rarest tree species in California, Oregon and Washington, United States of America, a\ud large, environmentally diverse region. Across 46 species, the mean annual temperature of\ud the range of seedlings was 0.120°C colder than that of the range of trees (95% confidence\ud interval from 0.096 to 0.144°C). The extremes of the seedling distributions also shifted towards\ud colder temperature than those of mature trees, but the change was less pronounced.\ud Although the mean elevation and mean latitude of the range of seedlings was higher than\ud and north of those of the range of mature trees, elevational and latitudinal shifts run in opposite\ud directions for the majority of the species, reflecting the lack of a direct biological relationship\ud between species’ distributions and those variables. The broad scale, environmental\ud diversity and variety of disturbance regimes and land uses of the study area, the large number\ud and exhaustive sampling of tree species, and the direct causal relationship between the\ud temperature response and a warming climate, provide strong evidence to attribute the observed\ud shifts to climate change