Although much of Craters of the Moon National Monument is covered by young lava flows, it supports a surprising diversity of plant communities. Uniquely adapted plants and a variety of abundant vegetation can be found here.

Over 661 different types of plants (taxa) have been identified in the Monument. Vegetation in different successional stages can be found on lava flows, in cinder areas, on kipukas, and in mountain and riparian areas. Many unique plants have developed ways to adapt and to survive the extreme conditions they face here.

The types and density of vegetation vary considerably and depend on such factors as geology, availability of soil and water, aspect, air temperature, and exposure to wind. The density of vegetation on lava flows depends primarily on the amount of soil available. Although lava flow surfaces support only lichens, vascular plants are able to grow in depressions on those surfaces. When basalt rock is very young, the only soil available is whatever blows into cracks and fractures. As soil develops within these cracks over time, vegetation can begin to grow. The depth of crevices, cracks, and depressions fixes the amount of soil and moisture that can be held. The size of the crack also determines the types of plants that will grow and what degree of protection they will have from harsh climactic conditions, such as extreme air temperatures and exposure to high winds.

Cinder cones support three different plant communities: cinder garden, shrub, and limber pine and/or juniper trees. These communities are determined primarily by aspect and by succession. In the early stages of succession, cinder gardens are colonized by species that produce spectacular spring wildflower displays. As soils develop on the cinders, antelope bitterbrush (Purshia tridentata) dominates shrub communities. And on the north-facing slopes where sufficient moisture is available, limber pine trees (Pinus flexilis) and/or juniper trees (Juniperus spp.) dominate.

Kipukas are islands of native vegetation that have developed on old lava flows surrounded by newer flows. Some kipukas in the monument have been protected from alteration by areas of rough lava and represent rare examples of undisturbed shrub steppe habitats. Dominant kipuka vegetation includes three-tip sagebrush (Artemisia tripartita), big sagebrush (Artemisia tridentata), bluebunch wheatgrass (Elymus spicatus), and needlegrass (Stipa spp.).

The portion of the monument north of U.S. Highway 20/26/93 is characterized by mountain and riparian areas that contain three vegetative types absent from the rest of the monument: Douglas-fir/mountain snowberry (Symphoricarpos oreophilus), upland quaking aspen, and riparian. The three types cover only a small percentage of the monument, but they provide critical wildlife habitat. The Douglas-fir forest (Pseudotsuga menziesii) is found on relatively steep, north-facing slopes of older cinder cones and along Little Cottonwood Canyon. The quaking aspen groves (Populis tremuloides) are in upland sites away from permanent stream courses. Riparian zones occur along creeks in drainages and are characterized by dense woody and herbaceous vegetation.

Scrublands

The most common vegetation type in the Intermountain West can be called sagebrush steppe, sagebrush grassland, shrubland, cold desert shrub, or simply western rangeland. Although there are differences in these terms and in the vegetation communities they describe, the common component among them is the presence of shrubs. A particular shrub called sagebrush dominates many of these communities, and occurs in combination with complex mixtures of other shrubs, grasses, and forbs. Climate, soil conditions, parent material and topography determine the general distribution of sagebrush and the various characteristics of shrubland communities. The dominant species of sagebrush in the northern part of Craters of the Moon is mountain big sagebrush. Mountain big sagebrush is widespread throughout the monument and is found in combination with the following types of grasses: bluebunch wheatgrass, Sandberg bluegrass, needle grasses, Idaho fescue, and cheatgrass. The five other species of sagebrush found at Craters are basin big sagebrush, Wyoming big sagebrush, three-tip sagebrush, early low sagebrush, and low sagebrush. Other common shrubs at Craters are antelope bitterbrush and rubber rabbitbrush. These two species are especially common on cinder cones. Sagebrush becomes a common vegetation component in areas with older substrates (geology) and where adequate soils have developed. The sagebrush steppe ecosystem provides an important watershed and valuable habitat for wildlife at the monument, including sage grouse, mule deer, pronghorn antelope, songbirds, and small mammals. Management protection afforded by the area’s wilderness status, along with the natural protection the surrounding barren lava flows provide, help keep many of the monument’s plant communities in pristine condition.

Nonnative Species

The National Park Service strives to preserve natural resources at Craters of the Moon National Monument and Preserve, including the native plants and animals. Non-native species are those which occupy lands as a result of the deliberate or accidental activities of people. Non-native species often alter ecological processes, disrupting food chains and nutrient cycles by out-competing native organisms in their own habitat. Diverse native plant communities which provide food and cover for a variety wildlife can be rapidly replaced by a dominant non-native weed which provides neither food nor cover for native animals.

Not all non-native plants present the same degree of threat to native plants and animals. Those capable of rapid spread are often called invasive weeds. Those with serious economic impacts are designated as noxious weeds. Noxious weeds affecting Craters of the Moon include spotted and diffuse knapweeds, leafy spurge, Canada thistle, and rush skeletonweed. Non-native invasive weeds are a significant threat to the remaining pristine vegetation communities within the monument. Management of noxious weed infestations through prevention of new introductions and by control or elimination of existing infestations is a high priority resource issue for the National Park Service at Craters of the Moon.

Several non-native birds make their homes at Craters. Some species such as Chukar or Gray Partridge may not have a significant impact on native species. Others can be a serious problem for native species. These problems range from Rock Doves which can change the nutrient levels in caves to Starlings and English Sparrows, which evict native birds from their nests. Craters is working with neighboring agencies and landowners to identify, locate, control and where feasible eradicate non-native species that threaten our natural resources. The issue of non-native species is likely to receive continued attention at Craters and around the world for many years to come.

Wildflowers

Despite the seemingly barren nature of the cinder cones and lava fields, spectacular floral displays occur at Craters of the Moon each spring. Starting with the arrival of the wild onion in late April and ending with the disappearance of the yellow blossoms of the rabbitbrush in September, some variety of wildflower can be found blooming within the monument's boundaries. The ability to grow in this harsh environment means overcoming a lack of moisture, meager soil, and surface temperatures that exceed 150 degrees Fahrenheit. Many of the unusual characteristics of the wildflowers are adaptations for survival.

Grasses

Although individual grasses sprout almost anywhere there is soil, grasses at Craters of the Moon are most commonly found as the understory (plants that grow beneath) of sagebrush steppe. Grasses play an important role in the ecosystem by stabilizing soil, helping hold moisture, and providing forage for wildlife.

Most grasses fit into two groups: bunch or sod-forming. With the exception of cheatgrass (Bromus tectorum), an annual European sod-forming grass accidentally introduced to the United States in the 1800s, Craters has almost exclusively native bunch grasses. Bunch grasses are classic desert plants that occur in scattered clumps. This type of growth pattern reduces competition for the limited soil nutrients and water available here. The principal grasses found at Craters include bluebunch wheatgrass (Elymus spicatus), Sandberg bluegrass (Poa secunda), needle grasses (Stipa spp.), Idaho fescue (Festuca idahoensis), and Great Basin wildrye (Elymus cinereus). These grasses are a vital part of a sagebrush steppe ecosystem that provides habitat for a variety of mammals and birds. Native grasses are a key component of successful rangeland fire rehabilitation, and in healthy communities they can provide resistance to invasive weeds.

Trees and Shrubs

The dominant tree in the northern half of Craters of the Moon is limber pine (Pinus flexilis). In the southern half Juniper (Juniperus spp.) is the dominate tree species.

Limber pine habitat provides important cover and food for wildlife. The large, wingless seeds of limber pine have a high energy content and provide a critical food source for rodents and birds. Clark's nutcrackers are major dispensers of seeds, caching groups of seeds in the ground. These cahes are relocated by Clark's nutcrackers, pilfered by rodents or are forgotten and germinate under favorable conditions. Limber pines are more abundant on aa than pahoehoe flows, but in both cases are able to grow where water collects, and especially where the trees receive protection from the fierce high desert winds.

In the southern protions fo the monument, stands of Rocky Mountain juniper (Juniperus scopulorum) and Utah juniper (Juniperus osteosperma) provide scarce structure and food source for birds and other wildlife. Although many were harvested by early settlers, some rare stands of old growth junipers (700+ years old) remain on the lava fields.

A few other species of trees are also found here, but in very limited numbers and geographical areas. The portion of the monument north of U.S. Highway 20/26/93 contains some Douglas-fir and upland quaking aspen stands. Douglas-fir forests are found on the relatively steep, north-facing slopes of older cinder cones and along Little Cottonwood Canyon. Quaking aspen groves are in upland sites away from permanent stream courses.

Several shrubs typically associated with mountain or riparian habitats are uniquely able to find similar growing conditions in the cracks of barren lava flows at Craters of the Moon. Examples include the fern bush and syringa. In order to resist being robbed of moisture by wind, the fern bush (Chamaebatiaria millefolium) grows inside deep crevices in the lava. It has aromatic leaves that resemble the fronds of ferns and that contain an oily substance which also helps the plants retain moisture. Native Americans rubbed the leaves over their bodies to repel insects. Deep crevices in the lava flows also provide the soil, moisture, and lower temperatures needed for the syringa (Philadelphus lewisii) plant to grow. Named after Meriwether Lewis of Lewis and Clark fame, this medium-sized shrub bears numerous large white flowers with four petals. It is very fragrant and serves as the state flower of Idaho.

Other common shrubs include sagebrush, antelope bitterbrush, and rubber rabbitbrush (Chrysothamnus nauseosus).

The dominant species of sagebrush in the northern part of Craters of the Moon is mountain big sagebrush (Artemisia tridentata ssp. vaseyana), which is part of a sagebrush steppe ecosystem that includes different types of grasses. Basin big sagebrush, Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis), three-tip sagebrush (Artemisia tridentata spp. tridenta), low sagebrush (Artemisia arbuscula spp. arbuscula),and early low sagebrush (Artemisia arbuscula spp. longiloba) are also found here.

Antelope bitterbrush provides browse for mule deer during the summer months, is a frequent host of thousands of tent caterpillars, and is identifiable by abundant yellow flowers and small, three-lobed leaves.

Rubber rabbitbrush grows to two meters tall and produces yellowish-green flowers from July to September. Native Americans made chewing gum by pulverizing its wood and bark. Rubber rabbitbrush can also be used to make tea, cough syrup, yellow dye, chest pain medicine, and is a small commercial source for rubber extraction.

Cheatgrass

Cheatgrass (Bromus tectorum) has drastically altered landscapes in the Snake River Plain and throughout the American west. This non-native annual grass arrived in shipments of European wheat during the late 1800s, and quickly established itself in many areas. Cheatgrass now covers over 100 million acres.

Cheatgrass is well adapted to the high desert climate and can out-compete many native plants. This is partially because cheatgrass uses a growth strategy unlike any other in the high desert ecosystem. While most desert plants are dormant during winter, cheatgrass germinates in the fall and spends the winter building roots and storing energy. By early spring, cheatgrass is ready to begin its aboveground growth while other plants are just breaking dormancy.

Since this strategy appears so effective, it is interesting that no native plants make use of it. Scientists explain this in two ways. First, it is possible that climate change has created a new "niche" that no native plants are able to exploit. Secondly, it is also possible that extreme climatic events which native plants can survive might someday wipe out this relative newcomer. In addition to germinating earlier, cheatgrass also uses subsurface water more efficiently and colonizes disturbed areas more quickly. As a result, native sagebrush steppe communities are increasingly rare, especially where wildfires or livestock grazing have occurred. In areas where cheatgrass dominates, both biological diversity and soil health decline.