Do plant communities commute?

ELISABETH M. BROWN

The idea that plants grow in plant communities is well-established,

and it’s a convenient shorthand to defining a group of plants and

animals that live in the same area and interact with each other. This

insect pollinates that particular flower, this bird nests in that

kind of cactus, this animal spreads that plant’s seed by eating its

fruit. Here in Laguna, the hillsides and canyons are covered by the

coastal sage scrub community.

With the advent of the cool and rainy season, our hillsides are

greening up. The few light green cactus plants that were so easy to

see among the browns and grays of the dormant shrubs are fading into

the background. On a recent walk through Laguna Coast Wilderness

Park, we found that nearly all of the shrubs that lose their leaves

during the drought season were leafing out.

In a couple of months the blue-white Dudleyas, also called Chalk

Lettuce, will bloom spectacularly. These big succulents grow mainly

on dry hillsides and sandstone cliff faces, but they’re easy to

overlook except at flowering time. Then they are suddenly very

noticeable as they grow long, graceful stalks carrying red

bell-shaped flowers.

In the Laguna coast area, Dudleya are a minor part of the

community, but in drier Baja it’s a different story. Below the border

the coastal sage scrub has more cactus and fewer shrubs, and the

sandstone cliffs are loaded with succulents.

Coastal sage scrub is not the same everywhere; to the casual eye

it looks pretty much the same, but the mix of plants changes with its

location. Some shrubs, like California Sagebrush, California

Buckwheat, and Bush Sunflower, are widespread, but others are more

variable.

Going north into Ventura county and a wetter climate, cactus and

Dudleya become scarcer, while shrubs grow taller and closer together.

An attractive shrub with bright green holly-shaped leaves called

Coyote Brush becomes more common in the community. Locally, Coyote

Brush is restricted by our drier conditions to growing only in damp

places.

How can one plant community have different mixes of plants? As

Reid Moran, a well-known botanist from San Diego, stated loudly more

than once, “Communities don’t move, plants move.”

Plants grow wherever conditions are favorable, and plants living

in the same geographical area have similar, but not identical,

requirements. That’s why the Dudleyas grow on dry sandstone cliffs,

but the Coyote Brush is found in wetter areas.

At the end of the last Ice Age, there was a general reshuffling of

North American plant communities as the climate warmed and dried, and

melting ice sheets uncovered new land to the North. Plants from both

wet, cool north and warm, dry south areas moved into the coastal

area. They grew where they found conditions to their liking, and

altogether they created coastal sage scrub, in a somewhat different

mix up and down the coast.

Botanists have different names for each of these variants: Diegan

CSS in the south, Riversidian CSS inland, and Venturan CSS to the

north. And what is Orange County? Venturan-Diegan CSS; a sort of

coastal sage scrub crossroads.

* ELISABETH BROWN is a biologist and the president of Laguna

Greenbelt Inc.