The Growth and Evaluation of Some Mexican Oaks and Other Trees in Los Angeles, California

Mexico encompasses innumerable ecological zones stretching from deserts to tropical rain forests and is a meeting place of temperate vegetation from the north and tropical vegetation from the south. Thus, it is no surprise that Mexico is blessed with an incredibly rich and diverse flora. One of the groups of plants that is unusually diverse in Mexico is the oaks (Quercus). With more than 160 indigenous species, Mexico is the primary center of oak diversity in the world. In 2001 I traveled to northeastern Mexico and with Mexican botanists made collections of several, handsome oak and other tree species. The oaks included Q. affinis, Q. crassifolia, Q. polymorpha, Q. rysophylla, and Q. sartorii. The seeds were germinated, seedlings grown on, and small plants out of 3.8-L containers planted out in 2005 at the Los Angeles County Arboretum and Botanic Garden in Arcadia near Los Angeles where they have been evaluated for landscape suitability for 8 years. Nearly all of the oaks and other species have grown remarkably well, clearly demonstrating their adaptability and suitability to the southern California climate. They received no special care other than occasional irrigation. They were unpruned for the seven years after planting out and most had attained about 10–15 m in height, had branches and foliage to the ground or nearly so, had trunks 12–20 cm in diameter, and were flowering and fruiting. That most of the oaks had adequate, if not superb, conformation and structure without any pruning after seven years from planting is a testament to the trees’ inherent ability to grow well without human intervention. Perhaps the most amazing tree, though, is a Mexican sycamore (Platanus mexicana) that after only six years in the ground is 17 meters tall and has a strong, straight bole, and has a 33-cm diameter trunk. These trees will be prized for their strong, robust growth of good to excellent conformation with few or no structural defects, handsome leaves, mostly evergreen habit, and suspected low-water use. This presentation will illustrate and discuss tree performance, cultural requirements, and landscape adaptability.