Cacti / Desert Succulents
More than most plants, the cactus seems perfectly suited to life in an arid climate. The cactus, especially the saguaro, has become emblematic of the American southwest. Eleven species of cactus are found in Canyonlands, though the saguaro is not one of them.
Cacti are plants that have succulent stems, pads or branches with scales and spines instead of leaves. Cactus pads are actually modified stems with a waxy coating. The prickly spines are modified leaves that break up the evaporative winds blowing across pad surfaces, and help shade the stem. Root systems are usually broad and shallow, and rainwater is soaked up quickly. Small rain roots actually grow as soon as soil is moistened by rain, and later dry up.
All plants photosynthesize, collecting carbon dioxide through holes in their leaves called “stomata” and converting it into sugar and oxygen. Cacti utilize CAM photosynthesis, a process unique to succulents. In CAM photosynthesis, stomata open only at night when the plant is relatively cool, so less moisture is lost through transpiration.
However, photosynthesis also requires sunlight. The CAM process includes a way of chemically storing the carbon dioxide until the sun comes out, when it can be used to complete the photosynthetic process. Stomata are like windows; they have to be open to let air and water in or out, but sunlight can come in even if they’re closed.
Despite their prickly armor, cacti are not immune to predators. Many rodents gnaw on cactus pads, and other mammals, including bears and humans, enjoy the sweet red fruit of the prickly pear.
Grasses grow throughout Canyonlands. Individual grasses sprout almost anywhere there is soil. Grasslands form in areas where wind-blown sediment and erosion have created a layer of soil that is several feet thick. Small grasslands form in potholes that have filled with dirt. Most desert grasses can be fit into two groups: bunch and sod-forming.
Bunch grasses are classic desert plants that occur in scattered clumps. This growth pattern reduces competition for limited soil nutrients and water. Indian ricegrass and needle-and-thread are bunch grasses. The relatively large ricegrass seeds are rich in protein and were an important source of food for Native Americans. Needle-and-thread has a sharp seed attached to a wound “thread” that drives the seed into the ground as it unwinds. Both of these grasses are perennial, becoming dormant during droughts. Ricegrass plants have been known to live over 100 years.
Sod forming grasses are what most people have in their yards. Galleta and blue grama are sod-forming perennials native to Canyonlands, and usually grow together. Unlike most desert grasses, galleta can withstand heavy grazing and is important forage for bighorn sheep and mule deer. The seed head of blue grama looks like eyelashes.
Cheatgrass is a sod-forming grass that was accidentally brought to the United States in the 1800s. This European annual is now established throughout the west and frequently takes over areas disturbed by fire or livestock grazing.
There is a great deal of exposed rock in Canyonlands, and much of it is covered by lichens. Lichens usually colonize north-facing surfaces since reduced solar radiation is an advantage for many organisms in the desert. Lichens also grow on healthy, mature cryptobiotic soil crust, and occasionally on live or dead plant material. Many species of lichen are found in Canyonlands.
A lichen is actually a simple community of at least two organisms, namely fungi with green algae or cyanobacteria, though sometimes with both. The lichen structure is more elaborate and durable than either fungi or algae alone. Green algae and cyanobacteria manufacture food via photosynthesis, while fungi provide a buffer against weather and are capable of extracting nutrients from soil and rock.
Lichens are well adapted to arid climates. They can carry on food production at any temperature above 32º Fahrenheit. Lichens can absorb more than their own weight of water, and can absorb temporary water like dew almost directly into their algal cells (the water does not need to go through roots and stems as it does in vascular plants).
Many plants benefit from the presence of lichens. The cyanobacterial component of lichens can transform atmospheric nitrogen (unusable to most organisms) into a form that is an essential nutrient for life. This is especially important in desert ecosystems, where lack of nitrogen is known to limit productivity.
Mosses and Liverworts
Mosses and liverworts are some of the many organisms found in Canyonlands that most people do not associate with deserts. Mosses can tolerate long periods of complete dehydration and occupy a variety of habitats in Canyonlands, including exposed rocks, cryptobiotic soil crusts, riparian areas and sometimes trees. They do best in shady canyons, north-facing slopes and at the bases of shrubs. Most liverworts must be near water to survive, and are very rare in the park.
Mosses and liverworts are small, primitive, non-vascular plants. They lack the conductive tissue most plants use to transport water and nutrients. Instead, moisture is absorbed directly into cells by osmosis. The most abundant mosses in Canyonlands can remain dry for years, and will rehydrate in seconds after contact with water. Some species begin photosynthesizing less than one hour after being moistened.
There is no complete inventory of mosses and liverworts in Canyonlands. At least 20 moss species are known to colonize cryptobiotic soil crusts, with Syntrichia caninervis being the most common. Grimmia orbicularis accounts for 80 percent of the moss found on rock surfaces.
Like all photosynthetic organisms, mosses are primary producers that build biomass through photosynthesis. They enrich ecosystems with organic matter, forming the basis of the food chain. As a component of cryptobiotic soil crusts, mosses trap airborne soil particles, reduce erosion, retain water and may enhance water infiltration.
Trees and Shrubs
Studying the woody plants of Canyonlands is made easy by the fact that, as a rule, they grow rather small and far apart. Limited by lack of water, shrubs and trees must disperse in order to survive. Once established, these desert plants are tenacious. Their roots will split rocks in search of nutrients, and many can live over 100 years.
Shrubs and trees are distinguished by their height (a less reliable indicator in the desert) and the number of stems (shrubs have several). Common shrubs include Mormon tea, blackbrush, four-wing saltbush and cliffrose. Mormon tea contains a drug similar to ephedrine, which is used in nasal decongestants. Blackbrush is a favorite food of desert bighorn sheep, despite its thorny nature.
Many trees grow in Canyonlands, though most are limited to the riparian areas where water is plentiful. These include netleaf hackberry, Russian olive, tamarisk and Fremont’s cottonwood. Both Russian olive and tamarisk are non-native species that can supplant native trees and significantly alter stream environments.
Mixed stands of pinyon pine and Utah juniper cover millions of acres in the southwest. These trees grow closely associated and dominate the landscape in dry, rocky terrain at elevations between 4,500 and 6,500 feet. In Canyonlands, pinyon-juniper woodlands thrive on mesa tops like the Island in the Sky and the Orange Cliffs west of the Maze. As elevation decreases, trees become more scattered.
Pinyon pines have crooked trunks, reddish bark and are very slow growing. Trees 4 to 6 inches in diameter and 10 feet tall may be 80 to 100 years old. Their root systems are extensive and often mirror the size of the above ground tree. Pinyons produce compact cones that contain tasty, protein-rich seeds called pinenuts. Pinenuts were a major source of food for Native Americans and are still popular today. Animals like the bushy-tailed woodrat, the pinyon mouse and the pinyon jay also prize them.
The Utah juniper is the classic desert tree. Its twisting, often-dead branches seem to epitomize the struggle of life with little water. When moisture is scarce, a juniper will actually stop the flow of fluids to some outer branches so that the tree has a better chance for survival. Scale-covered leaves and bluish, waxy-coated seeds help the tree conserve moisture.
Desert annuals like wildflowers are adapted to the arid environment in many different ways. These include thick, waxy coverings on leaves and stems which reduce exposure and thus evaporative water loss; small leaves which reduce water loss while the plant transpires or “breathes” and receive less solar radiation; and deep taproots to reach further into the soil or shallow widespread roots that absorb surface water quickly.
Despite these adaptations, most desert wildflowers avoid drought and heat by surviving as seeds or bulbs stored in the soil, sometimes for decades. These seeds will only germinate after significant seasonal rainfall, so wildflower growth in Canyonlands is highly variable year to year. April and May are generally the best months to see wildflowers, then again in early fall if there are a lot of summer monsoons.
Some desert plants take advantage of the nights’ cooler temperatures to flower. These evening-blooming plants include evening primrose, sacred datura, sand verbena and yucca. The yucca and the yucca moth have a fascinating nighttime association. After mating, the female moth gathers pollen from one yucca flower, packs it into a ball, and then flies into the night, locating other yucca flowers primarily by “smelling” with her antenna. She visits several flowers, each time laying some eggs in the base of the pistil and packing some of the pollen from her pollen ball down the pistil for her young to feed on. Thus she fertilizes the yucca flowers. Yucca flowers are only pollinated by yucca moths, and yucca moth young only feed on yucca pollen.