North American white pines   Robert Van Pelt
  Mar 02, 2005 18:27 PST 

Bob, et al.,
White pines have always been the most interesting to me.

I used to call them five needle pines but now must make a change. Most of the pines in southern Mexico are five needle, even though they are hard pines. Actually many have four or five, with some having even 6, 7, or 8.

Of the North American white pines, I find P. monticola the most variable. In central California it is found near timberline, up to 3,300 meters. Here it can be a large tree, developing deep, vertically furrowed bark that is often bright orange or maroon when mature. In the Puget Sound near Seattle, the tree has relatively thin bark that remains gray, even in age. Likewise in Idaho, but the bark is thicker, often forming perfect checks, leading to the name alligator pine which was one of the early common names. The easternmost population, in Avalanche Valley in Glacier National Park, is quite the site to behold. Here, just a few kilometers from the continental divide, the pine grows with Tsuga, Thuja, and Acer, reminding me of the forests along Lake Superior. There is even an understory Taxus to make the picture complete. Here, the pine has the thick bark in long, vertical plates just
like its Lake Superior counterpart. If it were not for the occasional Pseudotsuga, it looks alot like the Porkies. Even though the species are different, it suggests to me an ancient connection that was separated by the formation of the Great Plains.

The Mexican cloud forest Pinus strobus grows only in the very wettest forests and has relatively thin, tightly plated bark. Its closest relative is P. ayacahuite, which is a truly magnificent tree growing in slightly drier, mesic sites on a wide variety of mountains throughout Mexico. This tree is reminiscent of the magnificent P. lambertiana with huge, dramatic crowns of great character. The dry form of this tree, var. vietchii, makes enormous cones up to 65 cm long.

So far all the pines I have mentioned have seeds with full wings. A third variety of P. ayacahuite, var. brachyptera, has seeds with reduced wings. It grows in central Mexico. Partly overlapping in range and continuing into central New Mexico is P. strobiformis, sometimes known as P. flexilis var. reflexa. The seeds of this mountain pine have only the tiniest remanant of a wing. It is here where the pines begin to depend on corvids for their dispersal and not the wind. The furthest north of this multi-species grex is P. flexilis, a true nut-pine.

So this story of closely related pines comes full circle in Idaho, where P. monticola and P. flexilis both occur, although now with widely different ecologies. All of the pines I have mentioned are known to hybridize with each other where their ranges overlap, forming this giant range covering most of North America. The only exception is P. monticola and P. strobus, which are separated by a few hundred kilometers of North Dakota and eastern Montana.

The wonders never cease…