Plant Species of San Jacinto Mountain:
Distinguishing limber pine, Pinus flexilis, and sugar pine, P. lambertiana
Distinguishing limber pine, Pinus flexilis, and sugar pine, P. lambertiana
| Pinus flexilis, limber pine | P. lambertiana, sugar pine |
|---|---|
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| Fig. 1. Seed cones on the plant are the easiest way to distinguish limber pine and sugar pine from a distance in the field. The cones of limber pine are mostly held strictly horizontal, whereas the cones of sugar pine almost always hang downward. Left: limber pine, Pinus flexilis. Right: sugar pine, P. lambertiana. Click on the pictures for larger versions that show more of each tree. | |
Limber pine and sugar pine are easy to distinguish when cones are present, but difficult to distinguish without cones.
These two species are similar in many respects. They are both five needle pines. They both produce large cones. They often grow together in the same high elevation forests. They both have flexible branches.
The common name of limber pine, alluding to how flexible the young branches are, implies to some people that this is a difference from other pines. However, the young branches of sugar pine are equally flexible, so this is not a reliable difference. Even the older branches of sugar pine are so flexible that they bend down from the weight of their heavy cones.
The best way to distinguish these two species are with their cones, either by looking up at the trees themselves, or by looking down at the ground for their cones. Cones are always present on at least some trees, since it takes two years for the cones to mature, and the trees are not synchronized in the years they produce cones.
Looking up, the two species can be distinguished from quite a distance by the habit of their cones; see Fig. 1. In most cases, the cones of limber pine are held stiffly horizontal at the very top of the tree, perpendicular to the branch they are on, whereas the cones of sugar pine droop at the tips of the branches, appearing more as an extension of the branch. See the lower branches of the sugar pine tree shown in Fig. 1 right for the very characteristic appearance of sugar pine cones. Sugar pines are often magestical plants, tall trees with very long ~horizontal branches, with their very long cones drooping at the branch tips.
The tip of the tree is the best place to observe the horizontal cones of limber pine. If there are cones at the tips of the lower branches, they might appear to be drooping. But if you look closer, they are still stiffly perpendicular to the branch that they are on. See the lower branches of the limber pine shown in Fig. 1 left.
There is a reason for the different orientation of the cones. Limber pine has a special relationship with the bird Clark's nutcracker. Limber pine seeds remain in the cones, and Clark's nutcrackers have a specially-adapted beak to harvest the cones. The birds are very efficient in harvesting seeds from horizontal cones. They land on the branch tip, and then easily nab the seeds from the cluster of horizontal cones just below the branch tip. We've watched in amazement as a single bird can quickly and efficiently gather a large number of seeds (up to 100 can be stored in their pouch!) in just a minute!
The bird then caches the seeds, making as many as 20,000 caches a year! It returns to most of the caches during the winter and spring, but some caches are forgotten and grow new limber pines.
In contrast, the cones of sugar pine point to the ground, and drop their seeds on the ground when they are ripe. Most of their seeds are eaten or cached by squirrels. Many squirrels don't wait until the cones drop their seeds, and strip the seeds off the cones while they are still on the plant.
Looking down, it is easy to find cones of these two species lying on the ground. In most places, the ground under these trees is a vast graveyard of cones from the current year and previous years. Sugar pine cones are the longest of any pine species in the world, 20 to 60 cm (8 to 24 inches) long, and usually, but not always, have a long 2 to 6 inch (5 to 16 cm) stalk attached to one end. (The stalk can break at any point along its length, so sometimes stalks are shorter or even not present.) In contrast, limber pine cones are just 7 to 15 cm (3 to 6 inches) long, without a noticeable stalk. One quickly learns to see the difference on the ground at a glance; see Fig. 2. Until you pick up on the difference by sight, your foot is a handy measuring tool to check the length. Sugar pine cones are 2/3 to 2 x the length of your foot; limber pine cones are 1/4 to 1/2 x the length of your foot.
| Pinus flexilis, limber pine | P. lambertiana, sugar pine |
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| Fig. 2. Left: cone of limber pine, Pinus flexilis. The cone is 4" (11 cm) long. Right: cone of sugar pine, P. lambertiana. The cone itself is a short one, 7.5" (19 cm) long, with a 2" (5 cm) stalk.
Click on the pictures for larger versions. Both cone measurements were made using my 12" long boot for scale in the linked versions of the pix. | |
We don't recommend trying to determine the species of an immature plant, or a plant without cones; it is simply too unreliable. If you must, looking at the bark is probably the next thing to look at. We generally don't like to use bark for any tree, since it is so variable, especially with age of the tree. For example, the bark appearance is only about 30% reliable to distinguish Pinus jeffreyi and P. ponderosa.
Nonetheless, for those who want to try to use it, Fig. 3 shows bark of the two species from two plants that may or may not be representative. At least in our area, the bark of limber pine is a lighter color, and has cornflake like bits. In contrast, the bark of sugar pin is darker, and has longer flakes.
| Pinus flexilis, limber pine | P. lambertiana, sugar pine |
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| Fig. 3. Left: bark of limber pine, Pinus flexilis. Right: bark of sugar pine, P. lambertiana.
Click on the pictures for larger versions. | |
The habitat of the trees can also be helpful. At San Jacinto Mountain, limber pine and lodgepole pine are our highest-elevation pine species. Ridgetops and peaks often have just limber pine at their very tops, but usually lodgepole pine is lurking just 20 feet or so in elevation below the tops.
Limber pine is found at elevations of 8250 feet on the PCT a bit below Chinquapin Junction, to the top of San Jacinto Peak at 10,840 feet.
Limber pine is often found on ridgelines and on peaks for a very fun reason - because Clark's nutcrackers plant them there! The birds prefer at least some of their cache sites to have little snow accumulation, so they can retrieve their seeds during winter and early spring. Not surprisingly, ridgelines and peaks are often free of snow due to steep slopes and strong winds. Limber pine seeds are also cached in openings in the forest such as meadows, but limber pine isn't adapted to grow in those areas, so forgotten seeds in those areas don't survive.
In contrast, sugar pines grow in a wide variety of habitats, and down to significantly lower elevations.