Plant Communities of the San Gabriel Mountains
Table of Contents
Introduction What is a plant community? Why are the plants different in different places? What classification system is used? How are these pages organized?
Plant Communities Coastal Sage Scrub (Soft Chaparral) Chaparral (Hard Chaparral) Valley and Foothill Woodland Riparian Woodland Montane Forest Pinyon Juniper Woodland Joshua Tree Woodland
Angeles Crest Highway Road Guide: Plant Communities
What is a plant community? Munz in A California Flora, 1973, has the simplest definition:(a) Plant Community (is)...(a) regional element of the vegetation that is characterized by the presence of certain dominant species.The keywords are "regional" and "dominant". Regional is where you are and dominant is what you see. In other words, a plant community is what you see where you are.
In the San Gabriel Mountains, this might change if you merely turned 180°.
Why are the plants different in different places? In an area as complex topographically as the San Gabriels, many factors influence the differences in vegetation:
All these factors combine here to make the vegetation patterns on these mountains highly unusual. Schoenherr in A Natural History of California, 1995, expresses it this way:
- elevation: affects temperature and precipitation
- slope effect: north or south facing, affects temperature, precipitation, evapotranspiration, radiation
- available moisture: wet or dry, sometimes affected by amount of fracture and faulting of base rock
- soil: derived mainly from granitic rocks with lesser areas of schist and anorthosite
- topography: saddles wetter or drier depending on wind direction, peaks and ridges windier, canyons shadier and moister
- fire history: recent burns, evenness of ageThe Transverse Ranges (of which the San Gabriels are one) are ecologically unique. The side of these ranges that gets the greatest amount of precipitation is covered with drought-tolerant scrub vegetation known as chaparral. These scrub-covered slopes face southward and therefore receive direct sunlight. Even though these slopes get 30 to 40 inches of precipitation per year, the amount of evaporation is so high that moisture-loving plants cannot survive. 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. This side of the Transverse Ranges actually gets about half the precipitation of the south-facing side--about 15 to 20 inches per year--for the same reason that the eastern side of the Sierra Nevada is dry: It is in the rain shadow. Yet on this north-facing side of the Transverse Ranges, evaporation rates are lower and snow melts more slowly, so it is actually the moister side of the mountains. Such is the profound influence of slope effect.
What classification system is used? 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. More difficult to comprehend are names such as coastal sage scrub and chaparral. "Coastal" means between the mountains and the ocean which sometimes can be sixty miles apart! "Sage" is for the common plants collectively known as Salvias - white sage, purple sage, and black sage, while "scrub" refers to "stunted trees or shrubs". The origin of the name "chaparral" is more obscure. It is the Spanish word for a place where the evergreen scrub oak, chaparro, grows.
The plant communities are not uniform and they intergrade. Generally no sharp line divides them. But these being the San Gabriels, anything is possible. Thus, it is, that sometimes, on a knife-edged, east-west trending ridgecrest you can place one foot in one community and the other foot in a different one. Frequently, you can look cross canyon from under deep, cool shade of canyon oaks and see sun-baked chaparral only a few yards away.
How are these pages organized? Each plant community has its own page giving this information:
- The description lists the characteristics of the community by which the community can be identified without knowing the names of the constituent plants. It generally gives size, shape, spacing, stem form and leaf structure.
- The location tells where you would expect to find the community, whether it is on the coastal or desert side of the mountains, at what elevation, whether it is on the north- or south-facing slope and specific places where it is easily accessible or an outstanding example exists.
- Dominant species lists the larger plants that are most likely to be seen. Images of individual plants may be found by using the excellent CalFlora database.
- Outlined sections called Special Features highlight unique aspects of particular communities which are often overlooked.
- Links given For More Information are sometimes technical, sometimes about a certain species, and sometimes good pictures.
The Plant Communities of the San Gabriel Mountains
Coastal Sage Scrub (Soft Chaparral) Chaparral (Hard Chaparral) Valley and Foothill Woodland Riparian Woodland Montane Forest Pinyon Juniper Woodland Joshua Tree Woodland
Go to Field Guide to the San Gabriel Mountains: Natural History: Plants
Copyright © 2000 by Jane Strong
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Jane Strong
Updated January 21, 2000.