The former high school biology teacher founded the California Chaparral Institute, a nonprofit environmental group, and gives talks all over the state.
Through science, Halsey wants to show chaparral's subtle beauty and the limits of its remarkable adaptations to survive.
It is a lesson in the ecology of drought and fire.
The story of the senile Eastwood's manzanita, its muscular root anchored to fissures in the granite boulder, is as good a way as any to start the lesson. The stocky stalwart with a bright green head of leaves was actually born of fire.
As a seed, it fell from its parent and, by good fortune, landed in a crevice in the rock where water and dead leaf matter naturally amassed. It may not have sprouted for years. In fact, the seed may have just sat there, dormant, for more than a century.
Then came a fire. Smoke from its incinerated forebears woke the seed.
Scientists don't understand the precise chemical mechanism of this process, but it is the only way to germinate the five species of manzanita in Southern California, as well as many other endemic plants. As fire destroys one generation, it primes a new crop.
When the next rains came, the seed sprouted, its rock confines actually helping it. Manzanitas have strong roots that pry open fissures and hair-like capillaries that extract microscopic drops of moisture from between the crystals in the granite. In fact, the rock actually retains water much better than soil does.
While evaporation off the leaves pulls water and nutrients up through the roots like juice through a straw, the manzanita must drink slowly in this dry terrain. Its silver-green leaves point to the sky so the midday sun doesn't beat down straight on them. Fine hairs create a buffer layer of air around the leaf to limit wind from speeding up the evaporation process. And the microscopic pores in the leaves where the water exits -- the stomata -- are narrow, sunken and tangled with hair.
"The stomata on a manzanita look like an old man's ear," said Halsey. "Full of hair and wax."
This slows photosynthesis and growth.
So a century-old plant such as this one is only 15 feet tall -- and Southern California is a land of shrubs.
Hiking through the chaparral and coastal sage scrub of Southern California, Halsey never gave much thought to the shrubs. It wasn't until the mid-1980s, when he was teaching biology at Serra High School in San Diego on a windy day, that a crusty old sycamore leaf drifted through the door like a drunken epiphany.
