Small autumnal changes in the San Diego Zoo

This time of year some of us recall Midwestern or New England autumns; the mind's eye selects images: copper sumac and russet sycamore and ash, Mercurochrome red maple. Wind knocks leaves off one by one. Children run with leaves running at their back. Perhaps you remember (I do) crisp crackle underfoot. Perhaps, steeped deep in retrospective melancholy, you call up leaves burning and your memory of that acrid odor commandeers a thin spiral of smoke rising through skeletal branches, up, up, up and out, above your old neighborhood. Then off a favorite tree, one last leaf hangs, and the flat grey sky promises snow. But seasons sneak up on you here. One day it’s summer and the next day trees are trimmed with Christmas lights and the next day Is Superbowl Sunday, then, spring.

It was with such thoughts that I went to visit San Diego Zoological Society horticulturist Chuck Coburn. Would he, I asked, walk with me around the zoo and show me what happens to zoo flora in fall? Would he show me fail happening, autumn at work? He agreed, and at eight o'clock on a weekday morning we met outside the zoo offices. The sky was spotless, and a breeze scraped fronds on palms growing in a raised fieldstone planter. Against that breeze’s coolness. Coburn had draped a navy blue sweater around the shoulders of his white shirt. Coburn’s is one of those boyish faces that in middle age has retained an open, hopeful expression, and when he greeted me. I felt at once in good hands.

Directing my glance to the sky. Coburn said. ’’In fall, one of the most obvious changes is in light. Particularly in morning and evening. This time of year the quality of light is different. The light is lower in the sky, is coming through denser atmosphere, and therefore has a filtered appearance. It’s a beautiful light in many ways. It's the quality of light that we associate with great art: beams of light streaming aslant through windows’’

I knew what Coburn meant. The Emily Dickinson poem we all learned in school suggests it:

There’s a certain Slant of light.

Winter Afternoons —

That oppresses, like the Heft of Cathedral Tunes —

"The sun.’’ Coburn continued, “is of course the primary source of energy for our world.

Light controls the length of day and night and. generally, determines life cycles of living things. If people are tuned in. day to day. to nature, as farmers are. they notice these shifts. If a person has become citified, he often has become more removed from cyclical changes.”

Southern California. Coburn believes, isn’t the only part of the world where people are relatively unaware of seasonal turnover. In industrialized nations, because of insulation between themselves and the natural world, people also suffer, he said, from an “aseasonality.”

In fact, said Coburn, evidences of seasonality are everywhere. If we don’t see them, it’s because we’re not looking. “If we open our eyes. It’s like,’’ Coburn turned to me, grinned, “when you’re in love, then suddenly the world is absolutely vibrant, fantastic. It’s the same thing with seasonal change. It’s all here but sometimes we don’t see it.”

The zoo had not yet opened for the day when we walked through the gates. Zoo employees greeted Coburn, and he greeted them in return. He told me he'd been with the zoological society for 18 years, that he knew zoo plants and trees the way keepers knew the animals. His tone solemn, he said, "Some trees here I planted.”

Coburn pointed out deciduous trees planted along the area between the zoo front gates and the tour bus station. Deciduous trees, he said, shed their leaves in fall and become dormant until spring. In fall, he said, the profile of deciduous trees changes. By May, if we looked up through these trees, the canopy they provide would be thick; we would see little sky. But now, leaves have fallen off, there is less canopy, and we see wide expanses of blue.

We stopped. "Another way you know fall is here," said Coburn, "is sound. There’s a different vibrancy. It's deeper, heavier, more still. It’s a difference in rhythm. In springtime, there are all those rhythms going on simultaneously. Now, in fall, when growth is slowed, rhythms are slower. There are fewer songs being sung. There is less light bouncing.”

He directed my gaze toward an approximately 100-foot tall eucalyptus, the underside of its green leaves showing their silvery hue. "Look at that tree. It has a heavier feeling. By heavier I mean it’s less fresh, it’s more mature, it’s more rigid. This tree is losing vitality, storing juices, dosing down.”

Heading toward the Safari Kitchen, where workers were setting up open-air food stands for the day’s business. Coburn said that he had not started out with any particular interest in botany. At San Diego State, he majored in philosophy, with a special emphasis on religious studies and Eastern philosophy. After he graduated, he started gardening. “I wanted a way of expressing what I felt about life, and I didn’t know what it was. I didn't want to be a businessman. I’m not knocking business it just wasn't what I wanted.”

Zoo flower beds had been watered. The scent of damp humus mixed with the towering eucalyptus tree medicinal tang. Our footsteps sounded on the asphalt walkway, from a distance came the hoarse, anguished cries of the howler monkeys.

"Philosophy and gardening, given the way I look at the world, they work together. I think of plants as really, really lively and communicating. Plants are real smart and well adjusted. They don’t have strange emotional upheavals like people do. They just do what they do.”

What plants, both annual and perennial, do in fall, said Coburn, is to gather in on themselves (annual plants complete their life cycle in one year; perennial plants have a life; in of more than two years). "Plants anticipate seasonal changes. They don’t wait for cold weather to come, they get ready for it. The plant begins to shut down. Plant tissues harden. Colors generally deepen.

"Now the annual is going down, going back into the earth. At this stage in the life cycle, annual plants will lend to get dis and be more easily attacked by insects. Both annual and perennial plants at this time of year are more subject to bacterias. This is a natural thing and is exactly like a person’s body decaying. People led this process keenly." Coburn said soberly. "We want to resist it, but we can’t.

"You can generalize and say that this time of year nature as a whole is drawing in. When perennial plants are drawing back, drawing in. as they are now, it is almost like what in spiritual practice we call centering. During this time of year these perennials gather the energy together and go bade into themselves; they are preparing for spring — for buds."

Coburn hesitated, looked embarrassed. "I hope I am not taking these things too far, but this is how I fed.”

His wife, Coburn said, recently got a video from Blockbuster about colors. "You know how people will say that colors have different characters, like green or soft blue is feeling and yellow is clarity and cheer?”

At first, he said, he thought this colors and seasons video was a little silly. But then he thought about it, and it made some sense to him, that colors predominant at different seasons have something to do with how we experience seasons and seasonal change and therefore something to do with variances in mood and "feeling tone.”

"During spring and summer, when plants are actively growing, the range of colors is far wider. There is a greater variation in shades of green, also an intensity and vibrancy in the new green foliage. When fall comes, that color range narrows."

If he were choosing color crayons and wanted a green that would best express spring and summer color, I asked, what would he choose? “Definitely a lime green," Coburn said. And for fall? "A foresty deep-blue green."

What, Coburn asked, did I know about leaves? About their function? Little. I confessed. He explained. Leaves take in energy from sunlight and use that energy to convert carbon dioxide and water into sugars. Leaves' green pigment, called chlorophyll, harnesses the energy in sunlight.

I asked Coburn how, then, in fall, green leaves turned other colors. He answered that in order to make the most of sunlight, leaves often have pigments in addition to chlorophyll. These pigments absorb light of different wavelengths and pass that energy on to the chlorophyll. Among these pigments are the carotenoids (present in carrots), which can be orange, yellow, or red; xanthophylls, which are yellow; and anthocyanins, which are blue and purple. When a deciduous tree begins to shut down for the year, the balance among these pigments changes, and with that change comes a dazzling fusillade of yellows and pumpkin oranges, russets and nutmeg browns. "So,” Coburn concluded, “with leaves that are apparently changing color, what you are really seeing is the absence of green. Photosynthesis is shutting down and green cells going away. Therefore, you begin to see other colors that were already in the leaf."

At Safari Kitchens, we had taken a right turn and stopped at the Moreton Bay fig tree, a massive 60-foot-tall tree native to Eastern Australia. "Unlike the common yard in San Diego," said Coburn, "the zoo has imported so much from so many places — Northern and Southern hemispheres, new world and old — that it's not only the San Diego biological clock we see at work here."

The zoo, Coburn explained, has at least a dozen distinct temperature zones or microclimates. ‘The zoo’s western side, where we are walking, gets most of the breezes, if we get a frost, then it freezes hardest there. The zoo's eastern side is warmer, more protected, and is where we grow tropical plants."

Coburn allowed to a fondness for plants native to savannah and tropics, then added, all in a rush. "I like fruit trees really a lot. I have strong associations with my grandfather. He came out from Italy to the San Bernardino Valley. He was on Route 66 and he raised Concord grapes and figs, and he had a fruit stand there. He sold to all the Okies coming through.” Did Coburn grow up there? “No, my mother was an artistic soul. She didn't like the fruit-stand life. She went to San Francisco."

We examined the Moreton fig. Its trunk is as big around at its base as an elephant's waistline, and the bark is the same mottled gray as elephant skin. At elephant eye level, the trunk splits into three branches, and off the branches the stems produce a leathery leaf about eight inches long, green on top and copper-colored underneath. Leaves had turned brown, fallen from the tree onto the dirt.

Coburn stirred the leaves with a stick. "One of the finest composts you can have is a leaf compost made up of a tree's own leaves. Leaves covering the ground create a stable climate in which there is water in the right amount; there is proper drainage. The organic material from those leaves supports microorganisms. Earthworms will get in there, and you will get more water penetration into the soil."

In fall, Coburn noted, changes are going on above and below ground. Soil temperature is lower. I touched the crumbly dirt onto the fig leaves had fallen and thought it felt cool. The air at the tree’s base smelled tarnished, coppery. "This time of year, said Coburn, "microorganisms in the soil are less active. Leaves are being eaten and dying. Food isn’t coming through. So even if the plant were going whole hog, as it is in spring the nutrients would not be there.

"Just picture a root below ground growing through a warmer, more active, vibrant medium as compared to a colder, more closed medium. This time of year, it's much tougher going. Also, remember that in fall, roots have become woody and no longer as absorbent.

"A plant has to serve masters at both ends of itself to be successful. But in fall, except for the ends of a plant - growing tip and rootlets - the rest is simply having things done to it."

Headed toward the zoo restaurant to look at bamboos, we stopped before a black pine. The air knelled like those pillows stuffed with pine needles for sale in New England gift shops. Lateral branches struck off to either side of the main trunk. The bark felt rough and was grayish-brown. Once-green needles had turned brown and fallen onto earth around the tree. Coburn took a branch tip between his fingers. "It’s got little buds here that you can see at the growing tip. We call them 'candles.' Now, these tips are hard, not very flexible. This is a good example of what a bud is doing this time of year, as opposed to what it will become when spring arrives. In spring, it will soften and begin to produce new growth.

"For current history, you look closest to where a plant is growing. You look not only for what is happening at the growing tip, but further back also." Coburn pulled away yellowed needles. ‘See, here its losing needles. The energy is going toward the tips, and these older things." Coburn reached further down the branch, gathered a handful of brown needles, “are giving way and naturally falling down. You can say this pine is moving away from its past.”

Dew sparkling on filaments of a spider web spun between two of the pine’s branches caught our eye. "Where you get the dust and debris, you tend to get spiders and other insects that are not too helpful to the tree. We will come in here with a hose and with water pressure clean off the branches.”

We stopped then before a freeform rangy shrub covered with small glossy leaves and bright purple flowers, the Grewia ocddentalis, or lavender star flower. Coburn caught hold a stem and pulled it toward us. “You will see flowers on it this time of year only because it flowers almost all year. But here you can see that yellow pod behind the petals.” Coburn showed me a yellowish seed the size of an olive pit. ‘That is the ovary, or fruiting body, and it has begun to set up the seed.”

Arriving at the bamboo. Coburn smiled.

“Here” he said, running his hand down the bamboo’s long papery green leaves, "is a good example of something that is really San Diego: giant timber bamboo. Not our best-looking crop, but it is a good example.

"This is probably 25 feet high now. It has put out that much growth since April. When the shoots first emerge from the ground, they are sufficiently tender that people can eat them. The longer the bamboo grows, the woodier it gets. When it reaches maturity, as it has now. it’s incredibly strong.”

As a bamboo grows, fibrous sheaths protect its emerging tissues. The timber bamboo’s sheaths had begun to drop. Coburn pointed toward them with the toe of his tennis shoe. “To fertilize bamboo, one of the best things you can do is to let these sheaths fall on the ground and compost, because the silicon in the sheaths is one of the essential nutrients for this plant.

That’s why we leave them here. Again, nature knows what it’s doing."

I thought of Basho's poem about fall

sweeping the garden

but letting the temple keep

the willows' droppings

On our way to Fern Canyon, we stopped next to a coral tree, from whose branches hung only one brown sere leaf. “Gradually the food and flow of materials back and forth from this leaf has been shut down,” said Coburn, pulling the leaf off the branch, holding it up. Light shone through the leaf, producing an X-ray effect that allowed us to see the veins spread out across the leaf from its midrib. Several spots in the leaf’s interior looked like an intricate lace. Bites had been taken from the leafs edge. “A caterpillar ate there.,” said Coburn. "Had a meal that complemented its life cycle and then went on to better things."

Coburn handed me the leaf, said. "Imagine a positive and a negative flow. Sometimes there’s enough positive going on that a leaf is beating death. Other times, as in this case, death comes. ‘Boom, boom, boom!’’’

We passed the duck pond, watched for a moment the black-headed swans and small speckled mergansers swimming across the pond's surface, leaving behind them minuscule wakes. We crossed the walkway, strode past the bright red popcorn wagon, and stepped down into Fern Canyon.

Water roared down the grey rock. The air felt fat. thick with moisture. Immediately, the green surrounded us: the wide-leafed acanthus (larger here than it is as a potted house plant), jacarandas, heliconias, ferns, fig trees, banana trees, the two- and three-foot-long blade-like leaves of the rice paper plant seeming to burst exuberantly out from grey rocks set into the canyon’s sides. Bright colors dotted this wide compass of green red fruits trimmed the chamaedorea palms: bromeliads sat like macaws on tree limbs.

"Even in tropical forests," Coburn said, "most trees cannot grow nonstop. They have to rest. In San Diego, plants and trees that we consider tropical can be briefly deciduous.”

We approached a tall, overarching jacaranda tree. Coburn pulled a branch toward us. “If you look at this and don’t look closely, you think.

‘Ah. this is just pretty lacy foliage.’ But look at it more carefully, you see brown, tiny leaflets." I did. Dry little leaves. I touched them. They were brittle. I saw that these same leaves were drifting down onto dirt beneath the tree. I felt something in my hair. It was a leaflet from the jacaranda.

We looked at the sausage tree. Its long, brownish seedpods hung from the limbs, swayed in the swift breeze. "In summer," said Coburn, "where those big sausages are hanging now. there were flowers, deep, deep purple flowers. The tree's seeds are in those sausages, awaiting dispersal."

I said I was convinced. I saw fall. Coburn grinned, gazed down into a puddle of shadow cast on the walkway by the jacaranda. said again that he hoped he was not taking things too far. "A good way to reflect upon this phase of the life cycle of plants is this: It's like when some guys turn 40, they go out and buy a red Corvette and have an affair. The other side of that Corvette-affair story is that the guy is feeling his mortality. That same sense of seasonality we’ve been seeing here is embodied in people. Men and women arrive at the autumn in their lives and feeling their mortality upon them, begin to say. This is what really matters to me. I am going to be sure I do this.’”