Fitting the Pieces Together

The isolated factors described for each of Albuquerque's major systems - mountain, mesa, river, valley - fit together like the pieces of a jigsaw puzzle, forming ecologically integrated pictures. The information in the sequence below is an example of how each of the ecosystems analyzed on the previous pages can be viewed holistically, as they occur in nature. 

Present Bio-Profile of the Middle Rio Grande Valley

Plant Succession and Maintenance in the Bosque*

1. Ecological conditions in the bosque represent an abrupt change from those in surrounding mesa areas due to availability of ground water.
2. Trees in the bosque moderate climatic extremes by raising the relative humidity through evapotranspiration, lowering temperature through shading, and providing a buffer for wind and blowing dust.
3. Marked temperature inversions are produced when cold air from surrounding uplands flows into the valley at night. High relative humidity of the bosque adds a chill factor.
4. Four main tree types dominate the bosque. These are Rio Grande cottonwood, Russian olive, tamarisk (salt cedar), and at least four species of willow.
5. Exotic (introduced) trees such as Russian olive and tamarisk first became established in disturbed areas. Tamarisk grows particularly well along riverside drains where the root structure of native trees has been disturbed by dredging. More data is necessary to describe the succession pattern for exotics. Tamarisk appears to have the potential for replacing willow in some areas.
6. Where cottonwood grows it appears to be the climax species due to its greater height and canopy. Recent strands are mixed with Russian olive.
7. Thick cottonwood bosques are relatively unproductive for most wildlife, although they provide important cover. Disturbed areas, such as old burns which are returning to forest, provide more useful food production.
8. The succession pattern on burned areas varies with the severity of the fire, soil, water conditions, and other factors. These stages can be recognized in most burned areas:
• Grass stage: Low grasses such as drop seed, 
• Herb Stage: Yellow and white sweet clover, curly dock, sunflower.
• Scrub Tree Stage: Coyote willow often dominates due to its rapid growth; also cottonwoods sprouting from old roots, Russian olive, and some tamarisk. Exotic trees are most likely to make inroads during this stage.
• Mixed Bosque Stage: (most common) woods beginning to dominate with varying mixture of Russian olive, willow, and tamarisk; some scattered exotic ornamental such as Chinese elm.
• Mature Cottonwood Bosque: (climax community) Dense canopy shades out most other trees. These homogeneous stands are rare in the floodway due to wood cutting and channelization efforts.
9. Flooding seems to play an important role in reseeding burnt areas with trees. An even-aged mixed bosque east of the La Luz subdivision was seeded during a flood in the spring of 1941.
10. Root systems of cottonwoods and other large phreatic (meaning related to ground water) trees are vast. Fires burn only what is above ground leaving roots to sprout new trees. The estimated length of time for regeneration of a burned-over cottonwood forest with canopy is 20-30 years, depending on the severity of the fire.
11. While burned areas are regenerating, they provide important wildlife feeding areas. Large flocks of doves congregate in these old burns to find seeds and gravel.
12. All types of trees and some herbs are used by nesting birds. Dense thickets of coyote willow along watercourses appear to be most heavily used. Some birds such as the blue grosbeaks nest in curly dock 2-1/2 feet above ground, while the redwing blackbird prefers reeds and cattails for its nests.
13. Wintering mountain birds such as the Stellar's and scrub jays, bunco, robin, and white-crowned sparrow rely heavily on the bosque for winter food and cover.
14. Seeds of the Russian olive have been referred to as "river dates" by Albuquerque residents. They are utilized by red-shafted flickers, robins, crows, starlings, and even ducks when they grow close to the water or ground. The seeds remain on the tree through the winter and are an important wildlife food crop.
15. Mature trees help to keep the river in its channel. In addition, they can lower water temperature by providing shade. 
16. The cottonwood is self-pruning. Much of the deadfall and broken limbs remain on the ground making passage through thick bosque difficult and adding to the fire hazard.
17. Bosque vegetation is extremely hardy and resilient when compared to most southwestern vegetation. Most bosque plants tap the water table and therefore have an almost constant supply of water.

    * Reprinted from City Edges Study.