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Tucson Audubon Society
Know Your Habitat
by Larry
Liese (see Know Your
Habitat home page)
(Articles in this series first appeared
in the Vermilion Flycatcher, newsletter of the Tucson Audubon
Society. To receive the Vermilion Flycatcher in the mail, become a Friend
of Tucson Audubon.)
Habitat 7: Canadian Life-Zone, or fir forest
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Too bad. The hiking trails are still closed going up Mount Wrightson, so I guess a little crystal ball work is called for with regard to what’s growing at the higher elevations here. As the picture below shows, many of the trees died in this summer’s fires and, for safety’s sake, the trails won’t open soon (falling dead tree and erosion hazards). If we could go up there, we’d find that our final top zone of vegetation has quite a northerly feel to it. Winter snows are present months-long here, with sub-freezing temperatures to go with them. Vegetation is dormant much of the year, though daytime summer temperatures are mild. This zone is cooler and wetter than in the ponderosa pine forest, with precipitation of 25–30 inches per year. On south-facing slopes in our sky-islands, the ponderosa pines extend right up to 9,000’, while the fir forest is confined to north-facing slopes but can extend down to 7,500’. In the Santa Rita Mountains, the Canadian Life-Zone covers much of the higher terrain between Mount Wrightson and the head of Florida Canyon a few miles to the north. Terrain is usually rugged in this zone and, in the northern part of the state, fir forest is rarely seen on broad plateaus. Without the Crest Trail which runs north along the ridge from the summit, it would be hard traveling through this stretch of the Santa Ritas.
Fir forest usually contains a mix of tree species with Douglas fir and white fir the most prevalent. Also found are white pine and aspen. The forest is denser here due to the increased available moisture. This helps the trees endure the higher winds found on these upper reaches of the mountain range. The forest canopy is correspondingly denser with few, if any, understory species. A considerable layer of duff accumulates on the forest floor which, along with subdued light and harsh conditions, limits the growth of understory vegetation. The next zone that would normally occur above it is the Hudsonian Life-Zone or spruce-alpine fir forest. It is not present here in the Santa Ritas but is found in the higher Chiricahua and Pinaleno Mountains.
Most of the birds found in the ponderosa pine forest below are found here as well. A few of the species easier to find higher up include Steller’s Jay, Hairy Woodpecker, Golden-crowned Kinglet, Red-breasted Nuthatch, Spotted Owl, Northern Saw-whet Owl, Cordilleran Flycatcher, Pygmy Nuthatch, Hermit Thrush, Yellow-rumped Warbler (nesting in summer), Red Crossbill, and Yellow-eyed Junco. The Green Valley Christmas Count circle just extends to the high elevations of upper Florida and Madera Canyons, and many species only found here are welcome additions to the count. The count averages just below the 150 species level, quite a good target for inland locations.
When disturbed by fire, road building or high winds, quaking aspen sometimes move in and establish well-developed communities. These are called successional subclimax communities as they will eventually be replaced by the fir forest. Aspens are shade-intolerant. They reproduce chiefly from root sprouts, which are often present in diminished form in fir forests, waiting for an opportunity to spring into action. These aspen groves are rich wildlife communities, providing abundant food and cover for a wide variety of mammals and birds. Shrubs are much more common with the increased sun exposure and can include gooseberries and currants, Arizona rose, mountain and roundleaf snowberry, and Arizona and bearberry honeysuckle. It will be interesting to watch what happens in the Santa Ritas to see what happens in these burned areas. Particularly for our younger nature enthusiasts, perhaps a long-term photographic documentation project would be interesting to do. I’d suggest photos of Mount Wrightson taken from a fixed spot such as the intersection of the Vault Mine and Agua Caliente Trails.
Well, this issue’s column concludes the Know Your Habitat series. Have you learned a little about how conditions change as we move upwards in elevation? I hope so! I had wished to close the series showing a picture taken from Mount Wrightson’s summit looking back to Green Valley, but I guess that wasn’t meant to be. Anyway, get outside, be observant towards what nature shows you, and enjoy the wonders of our natural world. Good luck!
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This page was updated on 02/21/06