During the last weeks of October I had the good fortune to tour New Mexico. Our excursion took us to Albuquerque, Taos, and Santa Fe with stops in between. The viewscape there is much different than our own.

I’d like to share some of what I learned about the Middle Rio Grande River Valley’s riparian lands, known as “bosque” (the Spanish word for “forest”) to New Mexicans. Of special importance are the Rio Grande cottonwoods, particularly Populus deltoides wislezeni, a subspecies of Populus deltoides. This is not the eastern cottonwood found in northern New Jersey’s Raritan Bay Estuary and the Hackensack Meadowlands; nor is it the hererophylla or swamp cottonwood, found uncommonly in Cape May and Passaic County’s swamps. All these species of trees are Salicaceae, part of the willow family. Other members common to New Jersey include quaking aspen, big-toothed aspen, and black willow.

In New Mexico, the Rio Grande is the dominant river system. The river’s origins are along the Continental Divide in the San Juan Mountains in southwestern Colorado, into New Mexico, and finally it creates the United States southern border between Texas and Mexico, its 2,000-mile course ultimately emptying into the Gulf of Mexico. The stretch of the Rio Grande that separates the United States from Mexico is called the Rio Bravo by Mexicans.

The “Middle” in its name does not refer to the middle of the watercourse but rather to the river’s approximate mid-point where it passes through New Mexico. This is the stretch from Cochiti Dam, just north of Albuquerque, to 160 miles south in San Marcial, New Mexico. The “middle” is about one-third of the river’s length in New Mexico and 8 percent of its entire length. However, it is a section rich in tributaries in that it represents about 14 percent of the drainage basin. By our fall visit, much of the rivers’ tributaries were dry, since surface water is dependent on snowmelt and the very limited rain in this region. Most of New Mexico is a desert climate, and settlements and life itself are dependent upon water. There are six Indian pueblos (towns or villages) in this middle section—Cochiti, Santo Domingo, San Felipe, Santa Ana, Sandia, and Isleta.

We also visited the Taos Pueblo, a World Heritage Convention UNESCO site, on a tributary of the Rio Grande. The tributary is called Rio Pueblo de Taos or Red Willow Creek. The stream is considered sacred and may not be touched by non-native people within the confines of the settlement.

The Taos settlement is an important example of the interaction between American Indians and Spanish cultures. Its adobe residences and religious structures date back to the 1200s. It originated with the Anasazi Nation that once lived in Arizona, New Mexico, Utah, and Colorado. Their descendants still maintain and live on the site. The Native architecture retains its original appearance through traditional maintenance techniques. Earliest known occupation in the Taos Valley dates to around 900 AD.

In contrast, the Middle Rio Grande River Valley is not technically a valley but rather a series of basins, each slightly lower in elevation as you go south. The Rio Grande Rift, a geological feature where two sides of a fault are actually pulling away from each other, extends 500 miles from Colorado through New Mexico. To confuse things further, it is not a single rift as the name suggests but rather a series of basins that once each contained its own seasonal lake. To give this some geologic perspective, the Rio Grande Rift has been active for 20 million years and the Rio Grande has flowed in its present course for between one million and two million years.

The region’s weather is influenced by El Niño and La Niña cycles. During El Niño the precipitation rates increase, causing high spring water levels. Conversely, La Niña results in drought conditions. New Mexico is arid to semi-arid and trees are limited to mountains that capture rainfall or snow and to waterways caused by topography where this precipitation collects and moves southerly.

It was these water courses that compelled me to write about the Rio Grande cottonwoods. As we drove past vast expanses of desert-like landscape, we saw brilliant yellow ribbons of trees accenting the hillsides. The blue, primarily cloudless skies allow unfiltered light to cloak the yellow foliage with a brilliant shine, beyond description.

These yellow ribbons are the Rio Grande cottonwoods, marking dry water courses that are seasonally wet. Beneath the ground, an extensive root system still seeks whatever moisture exists. Along waterways, where there is a more consistent flow, coyote willows and cottonwoods grow over a broader expanse.

Pioneers and wagon-train scouts looked for a row of cottonwoods in the distance because they signified an important source of water in these otherwise arid lands. Pioneers also used the leaves of these trees for animal feed and herbal teas. And in a desert climate, one of the single most important things a cottonwood supplies is shade and shelter for both people and wildlife.

On close inspection cottonwood leaves are triangular-shaped and about two to 2.5 inches long and wide. Before autumn’s changes they are a shiny green with a yellow midrib and a coarsely-toothed margin. The stem is flattened such that the leaves shake back and forth in the wind like its willow relative, the “quaking” aspen.

The tree is dioecious meaning it is either male or female, not both. So a specimen will have a flower or fruit with just the female pistil on an entire tree, or a flower with just the male anther, which contains the pollen.

Unfortunately development, water management like levees and dams, and climate change threaten this ecosystem. Cottonwood trees rely on seasonal flooding for germination, yet the last great flood was in 1941. The damming of the Rio Grande and lack of annual inundation has caused seed germination to decrease greatly over the last half-century. Because of an absence of seedling cottonwood trees, many invasive non-native species like salt cedar and Russian olive have crept in and been allowed to flourish. The tree’s problems are compounded by its relatively short life of only 80 to 100 years.

We rafted a few miles of the Rio Grande near the Taos Junction Bridge in Carson, and also biked about five miles along the river in Albuquerque on the Paseo del Bosque Trail. The section we rafted was lined by coyote willow and cottonwoods, while the Albuquerque biking trail was lined only by cottonwoods. This habitat is essential for many migrating and endemic birds and other animals. We saw western bluebirds, warblers, kingfishers, ducks, and many other unidentified songbirds. Though we did not see sandhill cranes, they too make use of the area. Other animals include bighorn sheep, elk, mule deer, pronghorn antelope, cougar, black bear, bald eagle, and New Mexico’s iconic state fish, the cutthroat trout.

Like so many places in our nation, the loss of wetlands plagues the Middle Rio Grande. Between 1935 and 1989, more than half of its wetlands were lost. Forests are distributed largely between levees as opposed to throughout the wider floodplain. The lack of over-bank flooding means that areas with more abundant vegetation are prone to the risk of wildfires. Lack of flooding also allows more woody debris to accumulate.

Cottonwood does not burn as hot as some other wood but is good as a fire starter and as campfire fuel. The enormous stacks of logs we witnessed along the way would seem to indicate that New Mexicans rely a good deal on woodstoves and fireplaces.

In our travels we learned of the Native American uses for cottonwood. Good as building material, it is lightweight and rather soft so it is suitable for some furniture. It was used for cradles, fencing, large beams, rafts, and small boats. It is the primary wood employed to make drums since its workability makes it easy to hollow out; furthermore, it tends to rot from the core outward. An elk hide is stretched over it for the drum head. In addition, cottonwood roots were used to carve Kachina dolls, masks, and other ceremonial objects. The sacred poles and sun dance artifacts are also made from the trunks of these trees.

Cottonwood catkins were used as chewing gum. Further, all willows contain salicin, a chemical similar to aspirin (acetylsalicylic acid) that has pain-relieving and anti-inflammatory effects. The buds and leaves are antimicrobial so are also employed in the treatment of respiratory infections, flu, and colds.

Since the 1990s there have been efforts to restore bosque habitats along the Middle Rio Grande River Valley’s riparian lands. I don’t know how widespread these efforts have been but it is clearly a worthwhile endeavor.

Sources

• The Bosque’s Broken Heart: The Future of the Rio Grande Cottonwood, American Geophysical Union, Larry O’Hanion.
• Rio Grande del Norte National Monument and Wildlife Connectivity, New Mexico Wildlife Federation, Jeremy Romero.
• The Middle Rio Grande bosque: an endangered ecosystem. New Mexico Journal of Science, Crawford, C.S., L.M. Ellis and M.C. Molles, Jr. 1996.
• Bosque Background, New Mexico Museum of Natural History and Science, Lisa Ellis, Ph.D.