One consideration for any isolated populations of economically-valuable trees in such a heavily populated area with a 100+ yr logging history is that the current distribution of Sitka spruce may not reflect it's potential (or historic) distribution very well. Though not common, Sitka spruce shows up in old timber cruises of the early 1900s in the valley bottoms of Puget Sound (the Snoqualmie is the one I have info about). Although the species clearly does well in the fog zone, it is also clearly physiologically capable of handling periods without fog. As long as ground water is dependable, lack of stomatal regulation should not be a problem for the tree's survival.
Granted these are conjectures based on somewhat sketchy information. Andy Gray ________________________________________ From: Jason Hernandez [[email protected]] Sent: Wednesday, January 25, 2012 9:08 AM Subject: Isolated populations of Sitka spruce Sitka spruce (Picea sitchensis) is a characteristic tree of the coastal "fog belt" of the Pacific Northwest. Arthur Kruckeberg, in _Natural History of the Puget Sound Country_, shows a nice map of the "Sitka spruce" zone's extent relative to the "western hemlock/Douglas-fir" zone in Washington State. Essentially, the Sitka spruce zone extends in a belt approximately 20 miles wide along the coast and the Strait of Juan de Fuca, but ends at the Olympic rain shadow at the San Juan archipelago; it does not extend south through the inland waterways of Puget Sound. The explanation given is that this species lacks the ability to regulate transpiration, and so requires the high humidity of the fog belt. However, in my years of observations, I have found at least three populations of Sitka spruce in central and southern Puget Sound, far outside the regular "Sitka spruce zone." These populations are small in extent, with the species absent from the rest of the central and southern Puget Sound basin. I have been curious about what factors have allowed these populations to establish and persist outside the fog belt, but I struggle to formulate any workable hypotheses. Has anyone else worked with any similar phenomena? Jason Hernandez
