Growth Forms in Arctostaphylos glauca

Abstract

Arctostaphylos glauca has evolved two growth forms in the San Bernardino Mountains of Southern California. A chaparral ecotype of upright shrubs with relatively long leaves occurs in chaparral on the south and west sides of the mountain range. A desert woodland ecotype of low, compact, spreading shrubs with shorter leaves occurs in pinyon woodland on the north and northeast sides of the same range. The chaparral ecotype flowers early and fruits heavily. Upon periodic destruction by fire its populations are replaced by numerous seedlings. The woodland ecotype flowers late and fruits sparingly. Its lower seed reproductive potential is further indicated by the lower total number of floral units, by a lower proportion of fruit set, and by an apparent truncation of the flowering season before all the flower buds open. An alternative strategy, involving long life, compact growth form, and the exploitation of new soil resources by layering and vegetative reproduction in the absence of regular fire recycling has evidently adapted an old chaparral plant to recent desert woodland conditions.