Olympic National Park - Limitations to projections of climate change

Sep 2, 2010 (Last modified Sep 27, 2010)
Created by Dominique Bachelet
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Description
This map first shows the extent of mountain hemlock (beige area). This tree lives generally in moist sites, with enough snowpack to protect soils from freezing and to provide meltwater during spring and early summer. It is often found on cooler north-facing slopes. I have overlaid two drawings that show historical and future (much restricted) alpine climate conditions in red. A quick interpretation of this map would make you think that the habitat for this tree species is going to be significantly reduced in the future.
However, before thinking of many dead or dying mountain hemlocks throughout the Park it is important to realize that the west side of the Olympics is greatly buffered from regional warming by the proximity to a cold ocean so the east side of the Olympics will likely see more change as the climate warms than the west side, closer to the coast. Heat and drought stress will likely start on the east side of the mountains so monitoring for pest outbreaks and/or fire starts there would be most relevant rather than throughout the park if resources are limited.
Projections of future climate are also generally coarse. A grid cell where a climate model is run assumes homogeneous topography . The Olympics mountains have sharp peaks and deep moist valleys where the local weather is decoupled from regional warming because of cold air drainage, inversions and cold air ponding, close canopy evergreen forests maintaining cool moist conditions below their tall canopy.
I have traced in yellow the riparian corridors that offer cool moist conditions even during summers (healthy population of mosses and lichens attest to that) with many groundwater interactions with streamside forests.
Because the Olympics are rugged mountains, there are few meteorological stations and interpolated climate from any mountainous area is often a poor interpretation of local variations.
So while projections of future warming is an important wake-up call for managers, a closer inspection of the local conditions (coastal influence, riparian corridors, rain-shadow, scarce met station density) can help allocate resources more wisely to protect species of interest.
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Dominique Bachelet
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About the Map Author

Dominique Bachelet
climate change scientist with Oregon State University

Dominique received her Master’s degree in 1978 in Lille (France) and her Ph.D. in 1983 from Colorado State University with a thesis focused on biogeochemical cycles in the shortgrass prairie. In 1984 she went to U.C. Riverside as a postdoc simulating nitrogen fixing shrubs in the Sonoran desert then...