NPS Photo by Neal Herbert
Plants are critical components to all ecosystems, and Natural Bridges is no exception. Plants capture particulate dust in the air, filter gaseous pollutants, convert carbon dioxide to oxygen, provide animal habitat and possess raw materials useful to humans. A variety of adaptations in leaves and roots enable plants to survive the moisture and heat stresses here. Plant survival strategies are grouped into three basic categories: drought escapers, drought resistors and drought evaders.
Drought escapers are plants that make use of favorable growing conditions when they exist. These plants are usually annuals that grow only when enough water is available. Seeds may lie dormant for years if conditions are not favorable. Spring annual wildflowers are escapers. They sprout following winter and early spring rains, and sometimes again after late summer rains.
Drought resistors are typically perennials. Many have small, spiny leaves that reduce the impact of solar radiation, and some may drop their leaves if water is unavailable. Spines and hairy leaves act to reduce exposure to air currents and solar radiation, limiting the amount of water lost to evaporation. Cacti, yuccas and mosses are examples of drought resistors. Yuccas have extensive taproots that are able to find water beyond the reach of other plants. Moss, a plant not commonly associated with deserts, thrives because it can tolerate complete dehydration: when rains finally return, mosses green up immediately.
Another fascinating adaptation to resisting drought can be found in the Utah juniper, one of the most common trees in the southwest. During drought conditions, junipers can self-prune, diverting fluids from one or more their branches in order to conserve enough water for the tree to survive.
Drought evaders, the final group, survive in riparian areas where water is plentiful. Monkey flower, columbine and maidenhair fern are found in well-shaded alcoves near seeps or dripping springs. Cottonwoods and willows require a lot of water, and only grow along river corridors and intermittent streams where their roots can reach the water table easily.