|
ЧАПАРЕЛЬ, или креозотовый куст The Creosote bush (Larrea tridentata, formerly Larrea divaricata) is an evergreen shrub of the Zygophyllaceae family. It is a prominent species in the Mojave, Sonoran, and Chihuahua Deserts of western North America, including portions of California, Arizona, Nevada, Utah, and western Texas in the United States, and northern Chihuahua in Mexico. The wand-like stems of the plant bear resinous, dark green leaves and small yellow flowers. It also exhibits a characteristic odor of its creosote namesake. Some specimens have been found with heights of three meters, but typical plants do not exceed one meter.
Now, however, it has been shown that the root systems of mature plants are simply so efficient at absorbing water that fallen seeds nearby can not accumulate enough water to germinate, effectively creating dead zones around every plant. It also seems that all plants within a stand grow at approximately the same rate, and that Creosote Bush is a very long-living plant. From this, it can be concluded that all the plants inside a stand are of equal age.
Contributing to the harshness of the germination environment above mature root systems, young Creosote Bushes are much more susceptible to drought stress than entrenched plants. Germination is actually quite abundant during wet periods, but most of the young plants die very quickly unless there are optimal water conditions. Ground heat compounds the young plants' aversity to water stress, and ground temperatures can reach upwards of 70° C (160° F). To become established, it seems the young plant must experience a pattern of three to five years of abnormally cool and moist weather during and after germination.
Mature plants, however, can tolerate extreme drought stress. In terms of negative water potential, Creosote Bushes can operate fully at -50 bars of water potential and have been found living down to -120 bars, although the practical average floor is around -70 bars, where the plant's need for cellular respiration generally exceeds the level that the water-requiring process of photosynthesis can provide. Cell division can occur during these times of water stress, and it is common for new cells to quickly absorb water after rainfall. This rapid uptake causes branches to 'grow' several centimeters at the end of a dry season.
Creosote Bush's small leaves have a high surface-volume ratio, optimizing the rate at which heat escapes and water content is retained. Water loss is further decreased by the resinous, waxy coating of the leaves. Plants do drop some leaves heading into summer, but if all leaves are lost, the plant will not recover. Accumulation of fallen leaves, as well as other detrius caught from the passing wind, creates an ecological community specific to the Creosote Bush canopy, including beetles, millipedes, pocket mice, and kangaroo rats.
|