Canopy

Foxtail pines change their appearance as they mature.  John Muir (1881) describes the change,  “Wherever the young trees are at all sheltered, they grow up straight and arrowy, with delicately tapered bole, and ascending branches terminated with glossy, bottle-brush tassels.  At middle age, certain limbs are specialized and pushed far out for the bearing of cones, after the manner of the sugar pine; and in old age these branches droop and cast about in every direction, giving rise to very picturesque effects.” 

Muir’s vivid description of young trees as straight and arrowy accurately describes the canopy of most subalpine conifers including young Foxtail pines and their primary competitors Sierra Lodgepole Pines (Pinus contorta Loudon ssp murrayana (Grev. & Balf.) Critchf.).  The canopies of most subalpine conifers form nearly perfect right-circular cones.  Furthermore, branches rarely extend far from the bole.  The usual explanation for the canopy shape is an adaptive one — conical shape permits trees to survive heavy winter snowfall and high winds without breaking branches.  However, Kuuluvainen (1992) found that conical crowns are also optimal for intercepting light at high latitudes.

Figure 1. A bird's eye view looking straight down on the canopy of a young (left) and a mature (right) P. balfouriana canopy.

 

I have found that Muir’s description of older trees is incorrect.   Muir apparently failed to notice that branches do not “droop and cast about in every direction.”   Young Foxtail pines have conical canopies with a nearly circular cross-section (called circular canopies here) but adults have conical canopies with an elliptical cross-section (called elliptical canopies here), Figure 1.  The canopies are highly elliptical and the major axis of the canopy ellipse is nearly parallel to the local meridian. 

The elliptical-canopy habit is shared by nearly all adult trees that I have seen strongly suggesting that the trait is inherited.  Furthermore, the other members of subsection Balfourianae of Genus Pinus (Pinus aristata Engelm. and Pinus longaeva D. K. Bailey) share this habit (Rourke 1988a).  Randomly chosen stands of P. longaeva in the White Mountains of California and P. aristata in the Sangre de Cristo Mountains of New Mexico were studied.  Adults of both species have elliptical-canopies but saplings do not.  This observation suggests an ancient adaptation that has been inherited by these three closely related species.  

A randomly chosen Foxtail Pine in the Golden Trout Wilderness west of Lone Pine, CA.  John Bever is holding a meter stick and is standing on the east side of the tree.  The width of the canopy is nearly 3 meters.

Here is the same tree photographed from its south side.  The width of the canopy is approximately 1 meter.  The canopy is highly elliptical with the long axis point north-south.

Last updated April 15, 2001