the domain of multiple oak species. There’s the coast live
oak, the valley oak (deciduous, tall, sculptural, sweeping
branches, checkerboard trunk), and even a few black oaks
(deciduous, with bright, shiny, big leaves). Joining in are
bay trees, in the watercourses, and buckeyes, their leaves
turning brown well ahead of fall, which is a defensive shutdown strategy against the dry conditions.
Herlocker points out examples of the oaks’ web of
life. The mature trees have many cavities that birds and
insects use. An oriole nest hangs like a loose sack from
a branch in a valley oak; the bird wove it from fibers
shredded from a tarp. In mid-story, Herlocker would say,
“I hear a lazuli bunting” — or an oak titmouse or ash-throated flycatcher. We never see the birds.
Herlocker leads the way to a massive valley oak and
says, “This tree was around when the Civil War started.”
He estimates that it’s 300 years old, with a diameter of
five to six feet. It’s struggling now. Recently a limb as
large as most trees split off, but even lying on the ground,
it maintains a lifeline to the trunk. Despite its terminal condition, the tree is full of life. A close look reveals
hundreds of holes drilled into the trunk by acorn woodpeckers. This is their “granary tree,” where the birds
store acorns in their own personal pantry. There are also
hundreds of smaller holes, which Herlocker says were
formed by wood-boring beetles as they left the trunk.
Nearby we see another part of life: ghostly, sun-bleached
remains of victims of sudden oak death. The pathogen was
discovered in Marin County (“ground zero”) in the mid-1990s
and has spread through forests of Northern and Central
California, killing more than a million trees. Herlocker says
the current drought has slowed the spread of the disease,
which is worse in wet years. He puts it in perspective: “A
healthy forest is a mosaic of species, living and dead.”
To get to our final stop, we bump along the trail for
another half mile to Hidden Lake, actually a vernal pool,
one of those temporary ponds that fills up in winter and
spring and usually dries up in summer. In early sum-
mer it was totally dry, but its bottom was lined with an
assortment of plants specifically adapted to the quirky
boom-or-bust conditions.
Here in the preserve’s drier eastern half is a cross-
roads of diverse natural habitats. Herlocker attributes
it to “Marin’s scrambled climates” — different microcli-
mates and soil conditions close together. The trees are
scrambled too. Edging the pool are five different species
of oak that have found the right conditions: live oaks, a
particularly “stately” valley oak and three less prevalent
types. Blue oak (Quercus douglasii ) is deciduous, with
small, bluish leaves that absorb less heat, which allows
the tree to grow in hotter, drier places. Black oak prefers
shaded protected spots. Oregon oak (Quercus garryana)
prefers, well, Oregon. Near the southern edge of its range,
Herlocker calls attention to its shiny, dark green leaves and
the “intricacy of the branching.”
“Oaks are promiscuous,” is how Herlocker explains
the interesting phenomenon going on here that most of us
would otherwise miss. In this botanical melting pot, the
proximity of diverse habitats encourages cross-pollination
(wind scatters the pollen) and the creation of hybrids — such
as an oak offspring, sprouting from an acorn, that looks a bit
like both its parents, say, blue oak and valley oak.
Leaving the pool area, we almost step on a two-inch oak
seedling fighting for space in the grass. It’s a hybrid. Even
Herlocker can’t identify exactly what it is or its parentage.
Whatever it is, this seedling tells a story of the determination of oaks in the face of development, pathogens, drought.
I can’t help but think that they’ll be around when most
everything else is long gone. M
