Centuries Old and Busily Adapting

Peripheral (left) and axial (right) leaves - Chron photo

Redwood trees have been studied for over a century by scientists, lumber companies, and environmentalists. The groups have different agendas, of course, but no one was expecting surprising new knowledge to arise, such as the functioning of their leaves.

The trees’ peripheral leaves, like those on most trees, are food producers that convert sunlight into sugar through photosynthesis. But the axial leaves serve an entirely different role, researchers found — absorbing water...

According to the [UC Davus] study, published in the American Journal of Botany, a large redwood can absorb 14 gallons of water in just the first hour after its leaves become wet...

In some trees, when leaves get wet, they inhibit the photosynthesis process, the study found, But in redwoods, the different leaf types allow photosynthesis to continue — even in the rain and fog.

“Having leaves that aren’t for photosynthesis is in itself surprising,” said Alana Chin, a doctoral student in ecology at UC Davis and lead author of the study. “If you’re a tree, you don’t want to have a leaf that’s not photosynthesizing unless there’s a very good reason for it.”

The study also found that redwoods can change the location of their leaves depending on the climate. Along the west North Coast, water-absorbing leaves are found on the lower branches, leaving the upper branches for the sun-collecting and photosynthesizing leaves. In drier southern areas, the opposite is true with the water-gathering leaves near the tops of the trees where they can catch more rain and fog.

Muir Woods redwoods, 2007

Redwoods have not only developed specialized axial leaves to absorb water, but they move them higher or lower depending on climate conditions.

Walking through a redwood forest is a near-mystical experience. The coolness, the quiet, the towering trees, and even the forest smells are far removed from the urban and suburban worlds where most park-goers dwell.

But the interior life of the redwoods is not so quiet. They're observing and adapting to the changing weather in order to survive. To the science-minded, like your humble blogger fancies himself to be, that makes us appreciate them even more.

Sunday Worship

After we exited the ferry in Sausalito, I asked the Island visitors if they had ever seen a redwood tree. Yes, when Eisenhower was President. It was time to go again.

The cars were bumper-to-bumper on Highway 101 as we exited to Mill Valley. They peeled away as we approached Mount Tamalpais, so traffic was only moderate as we pulled into Muir Woods. Nevertheless, the parking lot was filled on late Sunday afternoon.

We ambled the main trail with dozens of other park visitors. The walkway was wide and worn, a blessing to those with hesitant hips and painful patellas. We were glad we had brought our jackets. The forest floor was dark and cool although it had been a bright 80 degrees in Sausalito.

The sun winked through the leaves. We craned our necks upward but couldn’t see the tops of the trees. We pondered the antiquity of a cross-section of a felled redwood, whose rings revealed that it had been born during the age of Charlemagne. No human eyes likely witnessed its birth, but its death had meaning that we memorialize.

We were invigorated; was the feeling due to the imagination or does the putatively higher oxygen content of the forest provide a scientific explanation?

People murmured softly, as if they were in a cathedral. Dwarfed by these giants, whose birth predated ours by centuries, perhaps they were. © 2007 Stephen Yuen