Plants Adapt to a Volcanic Landscape
Water is the limiting factor in plant growth and reproduction both on the lava fields of Craters of the Moon and on the surrounding sagebrush steppe. Plants have developed a combination of adaptations to cope with drought conditions. There are three major strategies:
1. Drought tolerance Physiological adaptations leading to drought tolerance are typical of desert plant species. The tissues of some plants can withstand extreme dehydration without suffering permanent cell damage. Some plants can extract water from very dry soils. Sagebrush and antelope bitterbrush exemplify drought tolerance.
Dwarf monkeyflower
Buckwheat
2. Drought avoidance Certain structural modifications can enable plants to retain or conserve water. Common adaptations of this type include small leaves, hairiness, and succulence. The small leaves of the antelope bitterbrush expose less area to evaporative influences such as heat and wind. Hairs on the scorpionweed reduce surface evaporation by inhibiting air flow and reflecting sunlight. Succulent plants such as pricklypear cactus have tissues that can store water for use during drought periods. Other plants, such as wire lettuce, avoid drought by having very little leaf surface compared to their overall volume.
3. Drought escape Some plants, such as mosses and ferns, escape drought by growing near persistent water supplies such as natural potholes and seeps from ice caves. Many other drought escapers, such as dwarf monkeyflower, simply carry out their full life cycle during the moist time of the year. The rest of the year they survive in seed form.
Pricklypear cactus
Ferns
Plant Microhabitats
Lava flows Most plants cannot grow on lava flows until enough soil has accumulated to support them. The park’s older volcanic landscapes, where soils are best developed, are clothed with sagebrush-grassland vegetation. On younger lava flows, bits of soil first accumulate in cracks, joints, and crevices. It is in these microhabitats that vascular plants may gain footholds. Narrow cracks and joints may contain desert parsley and lava phlox. Shallow crevices will hold scabland penstemon, fernleaf fleabane, and gland cinquefoil. Deep crevices can support the syringa, various ferns, bush rockspirea, tansybush, and even limber pine. Not until full soil cover is achieved can the antelope bitterbrush, rubber rabbitbrush, and sagebrush find suitable niches. On lava flows soils first form from eroded lava and the slow decomposition of lichens and other plants able to colonize bare rock. These soils can be supplemented by wind-blown soil particles until vascular plants gain footholds. As plants begin to grow and then die, their gradual decomposition adds further soil matter. These soil beginnings accumulate in cracks and crevices, which also provide critical shade and wind protection. Deep crevices provide lower temperatures favoring plant survival.
Rubber rabbitbrush
Syringa
Cinder gardens Compared to the lava flows, cinder cones are much more quickly invaded by plants. Here, too, however, volcanic origins influence plant growth. Compared to the relatively level lava flows, steeply sloping cinder cones introduce a new factor that controls the development of plant communities: topography. Here you find marked differences in the plant communities between the north- and south-facing slopes. South-facing slopes are exposed to prolonged, intense sunlight, resulting in high evaporation of water. Because of the prevailing winds, snow accumulates on northeast sides of cones, giving them far more annual water than southwest-facing sides receive. The pioneering herbs that first colonize cinder cones will persist on southwest-facing slopes long after succeeding plant communities have come to dominate north-facing slopes. It is on these north-facing slopes that limber pine first develops in the cinder garden. South-facing slopes may never support the limber pine but may be dominated by shrubs. Unweathered cinder particles range in size from 3 to 4 inches in diameter down to very small particles. They average about ¼ inch in diameter.
Cinquefoil
Wire lettuce
Ecological conditions at Craters of the Moon are generally so harsh that slight changes can make the difference for the survival of a plant or other organism. Life thrives in many rock crevices that are surrounded by barren exposed lava rock of the same physical composition. These microhabitats provide the critical shade and increased soil and moisture content required for plant survival. Over the years, particles of soil will naturally collect in rock crevices, which also have the effect of funneling precipitation into their depths. Their shade further protects these pockets of soil and water from wind erosion, excessive heat, and evaporation and leaching by direct sunlight.
Limber pines are the tree pioneers of the lava terrain. Their seedlings often find suitable conditions for germination in rock crevices long before surrounding landscapes support tree growth. Most common of all the park’s trees, limber pine is named for its flexible branches. Many park animals depend on this tree in some fashion for their livelihoods.
