Types

• More species of pines exist on mountains in the United States, Mexico and Canada than any other family of trees. Types like the bristlecone pine, whitebark pine, foxtail pine, limber pine and knobcone pine all occur high in the mountains. Among the spruces, the Brewer's spruce and Engelmann spruce are alpine evergreens. Mountain hemlock, Noble fir, subalpine fir, California red fir and Rocky Mountain juniper are other sorts of evergreens capable of sustaining themselves at great heights.
  
  

Size

• In many instances, the combination of poor rocky soils they must grow in and the high winds that buffet them will keep the size of alpine evergreen trees down. At the highest elevations, many of the trees that grow considerably larger elsewhere are no bigger than large shrubs. Whitebark pine, for instance, can grow to 50 or 60 feet tall in a sheltered spot with good soil, but high on a mountain, it is typically a sprawling shrub with a twisted contorted trunk. Foxtail pine can attain a maximum height of 50 feet, but in the mountains without protection from the wind, it struggles to reach 20 feet high.
  
  

Geography

• Since most of the significant mountain ranges on North America are in the western half of the continent, this is where the majority of alpine evergreen reside. In the East, the Carolina hemlock grows in the Blue Ridge chain at elevations up to 4,000 feet. In the West, many of the pines, firs and spruces are native to the Rocky Mountain States, the Sierra Nevada and Cascade Ranges and the mountainous terrain of Alaska and Canada. Ponderosa pine has one of the largest distributions of the alpine evergreens, growing from central sections of Mexico northward to southern British Columbia.
  
  

Significance

• The evergreen conifers of mountain settings are significant to the wildlife in these areas. A case in point is the whitebark pine. The seeds are a favorite of the Clark's nutcracker, which eats them and then winds up distributing them so the tree can spring up elsewhere. Many animals use the tree for food, such as bears. Squirrels will cache the cones and bears will find them, break them open and devour the seeds, with bears like the grizzly able to subsist on nothing but these seeds for long periods. Whitebark pine also has the ability to colonize sites charred by forest fire, being among the first trees to grow and thus provide shade for other seedlings. The species is a deterrent to erosion as well.
  
  

Time Frame

• The less than ideal conditions that many alpine evergreens endure often wind up slowing their growth. "Trees of North America" notes that it can take as long as 200 years for a whitebark pine to mature. The bristlecone pine is the oldest known tree species, with documented specimens attaining ages of over 4,600 years in California's White Mountains, according to the National Park Service website.