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.