Seedling characteristics and elevational distributions of pines (Pinaceae) in the Sierra Nevada of central California: a hypothesis

Seven species of the genus Pinus occupy a 3000-m elevational gradient on the western slope of the Sierra Nevada in central California. Three species of 3-needled pines replace each other abruptly over the mountainsides as do three species of 5-needled pines. The seventh species, a 2-needled pine, is found on the upper half of the mountainsides. Observed associations of pines on these slopes consist of a 2- or 3- needled species (or both) with a 5-needled species. A hypothesis is presented that interspecific competition between seedlings, ultimately for water, has led to the distributional patterns observed. This hypothesis is examined in terms of the morphological characteristics of seedlings and their needles that reflect their relative usage of water.