Vegetative and Reproductive Growth Patterns in Desert Willow (Chilopsis linearis (Cav.) Sweet)

Abstract

The patterns of leaf and fruit production of desert willow, Chilop- sis linearis (Cav.) Sweet, in relation to temperature and precipitation patterns in the Chihuahuan Desert of southern New Mexico were examined by harvesting shoot samples monthly during four growing seasons. On a site with 1.1 individuals per hectare, leaf production was about 5 kg-ha-1 and fruit production was about 1 kg-ha-1 in two years with dry springs and moist summers. In a year with a moist spring and a moist summer, leaf and fruit production was doubled. This high rate of production in the field during favorable periods supports previous laboratory studies that Chilipsis has a high acclimation potential under cool to moderate tem- peratures. However, in a year with a hot, dry spring and summer Chilopsis was adversely affected. This also supports previous studies that the net photosynthesis rate of Chilopsis was greatly reduced under high preconditioning temperatures and rapidly decreased as water potentials dropped below - 10 bars. Desert willow, Chilopsis linearis (Cay.) Sweet, is a small, deciduous tree. It varies from 4 to 9 m in height, with numerous long branches and willow-like leaves. The white flowers are orchid-shaped with purple stripes. The fruits are 10 cm or more long, and narrow, with wings of the seeds dissected into hairs (Kearney and Peebles 1960). Chilopsis occurs throughout the desert areas of the southwestern U.S. and northern Mexico (Hastings, Turner and Warren 1972). In the Sonoran desert, it occurs along the larger drainage channels with mesquite and other species requiring the more favorable moisture con- ditions of this riparian habitat (Shreve 1964). In the southern New Mexico region of the Chihuahuan desert, it is also restricted to larger drainages. Freeman and Dick-Peddie (1970) found Chilopsis in lower elevation riparian habitats of the Sacramento Mts., but not in similar habitats of the Black Range. Gardner (1951) found it in large arroyos and tributaries to the Rio Grande from the mouth of the Rio Puerco south to Las Cruces. Balding and Cunningham (1974) described the