This phenomenon, known as slope effect, is accentuated by the long, hot summers associated with southern California's Mediterranean climate. On the slopes that face northward, a coniferous forest extends nearly to the desert floor. Such is the profound influence of slope effect. There exists a confusion of classifications systems for California vegetation. Some are split into many small areas, sometimes only a few acres in size, while others ignore many of the special features of southern California.
Many authors use parts of one and parts of another or just make up their own.
This is because the patterns in California are very complex. This page follows Ornduff's system in Introduction to California Plant Life , part of the California Natural History Guide series. It was chosen because it includes streamside or riparian woodland as a community and because it lists bigcone spruce, numerically a very large part of the forest in the San Gabriel Mountains, as a component of the montane forest, both of which other popular systems do not. Classifications systems are often based on the structure of the community, its most common components and its location. Easy to understand examples are montane forest consisting of closely spaced trees in the mountains and foothill woodland consisting of widely scattered trees at the base of the mountains usually on gently-sloping land.