San Juan evergreens: A primer on forest’s winter sentinels

Observe ponderosa pines in the winter on one of San Juan Mountains Association’s Winter Discovery Walks, from Boggy Draw (pictured here) to La Plata Canyon or Junction Creek. Enlarge photo

Courtesy of Michelle Waltman

Observe ponderosa pines in the winter on one of San Juan Mountains Association’s Winter Discovery Walks, from Boggy Draw (pictured here) to La Plata Canyon or Junction Creek.

Winter moves along. The leaves of the aspens and cottonwoods are long past golden and lay frozen beneath the snow. Many oak bushes cling to their dead brown leaves.

While those deciduous trees are, in fact, still alive, the only trees showing signs of life are the conifers, with their green needles still photosynthesizing (making food) through the winter.

A conifer is a cone-bearing tree. There usually are larger cones that contain seeds (female cones) and smaller, barely noticeable cones that contain pollen (male cones). Except for ginkgos, they also usually have needles or scale-like leaves.

Conifers are the largest and oldest living trees on Earth. A few common, local conifers include: piñon pines, ponderosa pines and blue and Engelmann spruces.

Piñon pines often are found growing with junipers (yet another conifer) in pygmy forests, where the trees don’t get much taller than 30 feet because of limited water supplies. They can be found between 4,000 and 8,000 feet in elevation. The short, 1½-inch needles are arranged in bundles of just two. Piñon cones also are only about 1½ inches long.

Ponderosa pines are abundant in the San Juan National Forest. They dominate dry areas of the montane forest life zone, from 5,500 to 8,500 feet elevation. The root system of a ponderosa is well adapted to this dry environment: A 1-foot-tall sapling can have a 3-foot-deep taproot. If a tree is 100 feet tall, the root system will extend 100 feet into the ground as well as 100 feet out in all directions from the base of the tree.

Ponderosas grow relatively far apart so that trees are not competing for precious groundwater. Some of the ponderosa’s defining characteristics also protect it from fire. As the trees grow up, the lower limbs die and fall off. This keeps the limbs away from the ground, where fires are likely to burn. Ponderosas also have very thick, flaky bark. These thick layers take time to burn through, increasing the tree’s chance of survival.

Ponderosas have needles up to 7 inches long and are bundled in groups of three. The cones are fairly large, ranging from 3 to 4 inches in length. Ponderosas that are flat on top are at least 200 years old - maybe even 500.

Moving up in elevation, we find spruce trees, easily identified by their needles. On first contact with a spruce, the needles feel sharp or spiky. A single needle, when rolled between the thumb and index finger, feels edged or square. The easiest way to remember how to identify a spruce is: “square, spiky spruce.” Spruce cones grow at the tops of the trees and point downward.

The blue spruce is Colorado’s state tree, so it often is found outside its natural habitat planted in yards and parks.

Blue spruces typically grow in moist, shady areas and thrive at elevations of 7,000 to 9,000 feet. The waxy coating on the needles often gives the tree a bluish appearance.

The Engelmann spruce, formerly called silver spruce, is similar to a blue spruce. The easiest way to tell the trees apart is based on elevation. Engelmann spruces live around 9,000 feet to tree line. These trees often are found mixed together with subalpine firs.

There are many more conifers in Southwest Colorado than identified here. One valuable resource for more information is www.swcoloradowildflowers.com. Another great way to investigate conifer trees is to get outside. Bring a tree field guide (available at any San Juan Mountains Association bookstore), and learn more about these beautiful green giants of winter.

MK Thompson is the conservation education assistant for the San Juan Mountains Association.