Page 28 - The Black Range Naturalist Vol. 4, No. 3

Seeds are eaten by small mammals (Abert’s Squirrels, chipmunks, mice), insects, and birds.
Other interdependencies: Abert’s Squirrels are prey for larger hawks, but they are not a major food source for mammal predators.
those at higher elevations are more often found in stands of mixed conifers. The ecotones between these zones vary in “width” depending on local conditions. Ponderosa Pines may be the dominant species in a tree and shrub community which includes Douglas-fir, juniper, Southwest White Pine, manzanita, Chokecherry, etc.
Ponderosa Pine likes the sun. Its growth rate can be cut in half by partial (50%) shade. Because of this, Ponderosas can often be found in stands where the trees are of the same age. These factors, the quality of the wood, and its growth habit (tall straight and of significant girth) make this tree a favorite of loggers.
The cones of the Ponderosa Pine take 2 years to mature. Flowering occurs during the first year (April to June). The cone reaches maturity during the second year and disperses seeds during August and September. Seeds are small and seldom fall farther than 100 feet from the parent tree. It may take up to 23,000 seeds to weigh a pound, although as few as 7,000 may weigh that much.
Every 8 years or so Ponderosas will produce an especially heavy seed crop. In about a quarter of the years, very few cones are produced. Each cone contains about 70 seeds. By age 7, this species can produce cones and may continue to do so for more than 350 years.
Abert’s Squirrel (a.k.a. Tassel-eared Squirrel), Sciurus aberti chuscensis, photographed in Railroad Canyon of the Black Range on 7/23/2017. There are currently nine recognized subspecies. This subspecies is found in SE Arizona/western New Mexico. They are associated with Ponderosa Pine, using the needles for nesting material and eating the seeds. The range of an individual varies by season and location but is generally between 10 and 30 acres, though it can be as high as 60. Although Abert’s Squirrels may nest in Ponderosas, they do so on the branches since these pines seldom have cavities large enough for a nest. Gambel Oaks - sometimes cottonwoods - are more typically used for nesting. Abert’s are omnivores, but feed on Ponderosa Pines throughout the year (seeds, inner bark, buds, and young cones).5
Pinyon Jays and Clark’s Nutcrackers are among the bird species which cache Ponderosa Pine seeds, and to the degree that they forget the cache, they disseminate seeds away from the parent trees.
Abert’s Squirrels will begin the season by eating immature seeds in May, and by the peak of the “harvest” they may consume the seeds of 75 cones a day. They will continue to eat seeds as long as they are available. They also eat the inner bark of twigs year round, but especially in winter (November to April). Besides the seeds, they will eat new cones in their entirety, only the pollen is eaten from dried cones.
Ponderosa Pine seedlings are food sources (and are otherwise damaged by) rabbits, pocket gophers, squirrels, and deer. Cattle and sheep also destroy them.
Following the excessively intense grazing which characterized the Southwest until the first quarter of the 1900’s, Ponderosa seedlings developed into dense stands, facing no competition for nutrients or sun. These large stands of single-age Ponderosas were a fertile food source for a variety of insects, including:2, 6
Western Pine Beetle (Dendroctonus brevicomis), which can kill older trees and young healthy trees during eruption. A study in Northern Arizona found this to be the most common Dendroctonus species at elevations around 7,000 feet7);
Roundheaded Pine Beetle (Dendroctonus adjunctus) is often associated with the Western Pine Beetle;8A
27