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…

North American white pines - continued   Robert Leverett
  Mar 03, 2005 08:16 PST 

Bob and Lee:

Bob, fascinating material.

Within the range of the eastern white pine, have either of you
observed discernable differences in physical characteristics
latitudinally or longitudinally?

Geneticist Alan Gordon once told me that if you take white pine seed
from say northern Alabama and plant it in say New Hampshire, it will
grow very fast, but be highly susceptible to the cold. In general he
says that you don't want to move the seed of a species more than a
couple degrees latitude. Lee, you've often discussed the great
difference in the tolerance to cold of the northern white pines versus
their southern brethern. Have you noticed physical differences that you
would attribute to a change of climate in the eastern white pine?   

Re: North American white pines - continued   Lee E. Frelich
  Mar 03, 2005 09:10 PST 


Yes, I think the dense tufts of foliage that northern pines develop helps
keep the foliage from getting damaged by cold and desiccated by winds
during the winter. The red bark of northern white pines may also be an
indication that more carotenoids are present in the tree which would help
protect the trees from sunlight damage during the long summer days with sun
coming in at a lower angle than further south.

We know from a number of common garden studies that most species of trees
do not do well if you move them more than 1-2 degrees latitude from their
seed source. Trees from Cook Forest or the Smokies would not have the
slightest chance of surviving in the Boundary Waters because of winter cold
and short length of growing season.

RE: North American white pines - continued   Gary A. Beluzo
  Mar 03, 2005 10:36 PST 

Lee and Bob:

So...during the onset of glacial periods and then interglacials, tree
species either have to "find" similar climatic regimes (less than the to the
1-2 degrees latitude range you mention)through gradual migration, natural
selection of stranded populations will result in new ecotypes, or a species
will become extinct. I wonder what the "climatically tolerant" ranking would
be for our eastern tree species. Any ideas?