Biology Reference
In-Depth Information
State University, also served as a guide. Liba's specialty was none other than the
'akiapōlā'au—
'aki
for short—the renegade honeycreeper that had evolved to become the is-
land's de facto woodpecker. For several weeks, she had been watching a male make feeding
trips to a female and their young. Although it feeds like woodpeckers and sapsuckers, the
'aki does not nest in tree cavities; instead, it makes a cup nest in the terminal branches of the
'ōhi'a tree. If we were lucky, our group would see this rare honeycreeper, but to find even
one of the remaining 600 pairs spread over several thousand square kilometers in only three
hours would indeed require a blessing from the birding gods.
We walked through a stand of tall 'ōhi'a and giant koa trees—Hawaiian old
growth—which gave way to meadows and back again to forest. For a biologist and lover of
fantasy fiction, our hobbit-like experience of walking through open glades interspersed with
groves of giants with their odd architecture was like a walk through Tolkien's Middle Earth.
It's an ancient landscape, too: some of the 'ōhi'as have been carbon-dated at over 400 years
of age, making them possibly the oldest nonconiferous trees in the entire United States.
Jack's knowledge of Hawaiian natural history flowed nonstop. He pointed out that the lack
of native mammalian herbivores had allowed native vegetation over evolutionary time to lose
defenses against being eaten: spines and thorns and waxy leaf cuticles and other chemicals
that make plants taste bad. Thus, the native raspberry in Hawaii has many fewer and softer
thorns than do raspberries elsewhere, the native nettle has lost its stinging hairs, and the local
mints no longer produce the strong aromatic oils that emit their characteristic fragrance in
other lands. David crushed the leaves of a nearby 'ōhi'a, expecting the small, fuzzy foliage
to release a strong guava-like aroma. This dominant Hawaiian tree is a member of the eu-
calyptus family, known for the powerfully volatile oils infusing the trees' leaves and bark.
He inhaled deeply, but there was no smell. Like other native Hawaiian plants, the 'ōhi'a no
longer needed to repel large browsing mammals as had its evolutionary ancestors, and so,
over time, its costly perfume factory had shut down.
Koa (
Acaciakoa
), the other old-growth tree species here, is one of a strange-looking group
of acacias. Most wildlife tourists associate “acacia” with the umbrella thorn acacia,
Acacia
tortilis
, the flat-topped tree of postcard East Africa. Most amateur botanists recognize the
genus
Acacia
by its bipinnate compound leaves and wicked thorns. These features aren't
present in the koa, though. That's because there aren't any leaves, at least not on adult koas.
Instead, koas photosynthesize with structures botanists call phyllodes—flattened petioles, or
leaf stems, that serve the purpose of leaves and resemble small green boomerangs.
Acacia
species with phyllodes instead of leaves are a phenomenon seen only in Australia and the Pa-
cific islands. Nearly all Australian acacias lack thorns and photosynthesize with phyllodes.
And with no giraffes or elephants in the Hawaiian fauna, koa trees, of course, didn't need
thorns either.
