The Arbornaut, page 9
With the equipment list squared away and a beginner’s sense of the logistics for scaling tall trees, I still needed to think harder about what trees to climb, how many, and why. Field trips into the bush to locate study trees required booking a university car, packing a full set of camping gear, scrutinizing maps to locate rain forests, and learning the nuances of driving in rural Australia—not just keeping to the left side of the road but also anticipating kangaroos, logging trucks, and mud. On the second trip, I happily went solo and visited three national parks—Dorrigo, New England, and Royal—all primary rain forests in New South Wales safeguarded from poachers and clear-cutting due to their preservation status. On the first day, I set up a meeting with a retired Dorrigo forester whose name peppered the field guides in the botany library. Alex Floyd had authored the only identification guides to Australian rain forest trees at the time. I sent him a handwritten letter, as was the conventional communication of the late 1970s, and he replied to confirm our date to look at trees. I was especially eager to identify species in the field, and Alex kindly agreed to give me some initial pointers. We met in the parking lot at Dorrigo National Park in the pouring rain. It was easy to find him because no one else was there. In Australia, the only remaining rain forests to have survived a century of logging tended to be stands on extremely steep hillsides where the timber was too difficult to extract. So we two soggy botanists proceeded to slog along slippery slopes and try our best to look up at silhouettes of different trees while constantly wiping raindrops off our glasses. Due to our shared passion for rain forests, Alex became a loyal colleague, perhaps because there were only a handful of us throughout the entire country who learned to identify these trees. (I later taught botany to his son when he was a college student!) Starting at the edge of the parking lot, Alex taught me to identify sassafras: he crushed a leaf so I could appreciate its beautiful scent, like that of the North American sassafras growing on the forest floor of my childhood; the Australian version was a tall tree, though, not a small understory plant. The aromatic scent turns out to be the only similarity between these two species, which grow half a world apart. (Here was a future research project, to investigate how sassafras aromatics evolved separately in a temperate understory plant and a tropical tree.) Next, we confronted the red cedar, highly valued because of its outstanding timber. Popular for furniture making, it earned local notoriety as the species responsible for the clear-cutting of Australia’s rain forests (although people enacted the deforestation, not red cedars). And as one of Australia’s only deciduous trees, it piqued my leaf-loving curiosity for research potential, although Alex cautioned me it was quite rare due to continued poaching.
As we walked through the forest, blithely staring upward to the treetops, then looking down to plant our boots on the steep, muddy trail to avoid slipping, I saw blood seeping through the fabric of my bedraggled shirt. Had I been cut somehow? I cautiously peered inside. Nestled between my breasts was a slimy black, puffy creature over an inch long. I had no idea what was attacking me. Terrified, I could hardly speak and reluctantly described this invader to my senior colleague. He chuckled and said, “Just a leech.” Alex was very blasé, but I was horrified. In ignorance about the tropics, I had never heard of leeches living in the Australian rain forests, nor did I know how to remove one from my chest. Alex suggested to just leave them alone, and once they had a full blood meal they would drop off; that was not very reassuring, especially when a large leech was feeding on my chest. But by the end of the day, I had given a blood meal to at least a dozen leeches and eventually stopped concentrating on their invasion—Alex too had attracted his own population. Welcome to the Australian rain forest! Finding many more of those slippery suckers on diverse parts of my anatomy at the end of a wet day, I disgustedly flicked them out the window of the roadside motel. Even though their bite and subsequent bloodletting were not life-threatening, their attacks were a personal affront and hence I developed a lifelong mission to minimize their attacks. My initial combat method was to simply brush them off once discovered. But tossing them as you walk is considered impolite bush behavior, because they usually latch on to the person walking behind. Over the years, I resorted to more creative modes of leech removal: burning, cutting, salting, squishing, and even sewing canvas boots to my pants to prevent invasion, since leeches usually crawl up shoes to socks and then inside pant legs to the groin, seeking the warmest and coziest body crevices to suck a blood meal. As with so much rain forest research, I ended up with more questions than answers: Why are there no leeches in the American tropics? Does another organism occupy their ecological niche? Do these creatures inhabit the Australian canopy, or just the forest floor?
Alex introduced me to several dozen tree species, with handy tricks for field identification such as the smell of sassafras leaves or the red flowers of flame trees (Brachychiton acerifolius). Sometimes a little knowledge can be dangerous, and this field trip provoked many sleepless nights trying to sort out which trees would be both safe for rigging and offer unique foliage traits to study. As a solitary researcher and a woman, I also needed to think strategically about safety in the field. Australian rain forests are a pretty wild and remote region of the planet. Admittedly, I felt slightly apprehensive about driving, sleeping, and exploring alone, but simply had to buck up courage and move beyond those small-town fears of the unknown.
A discussion phase is critical for designing effective research. How could I mark branches overhead and find them again month after month? Could I camouflage each climbing site from human marauders? Which species offered the most intriguing leaf traits? Which trees were safest for climbing? Those friends in the caving club had been helpful with preliminary logistics, but now I required insights into the science. So I turned to the gang of coral reef students located next door in the Zoology Department. In terms of high diversity, rain forests are the land-based counterpart to coral reefs. The marine students and I found plenty to talk about because we shared similar questions about biodiversity and how to sample accurately in our complex ecosystems. Whereas I wanted to figure out how many leaves and at which heights I should sample to document foliage, they needed to determine how many fish on which patches of coral reef would answer questions about marine ecosystems. I needed an experimental design (essentially a recipe) for collecting field measurements over several years and then analyzing the results. But I also had to contend with different safety factors—snakes, leeches, muddy roads, biting ants, rotten branches, finding drinking water, worn ropes, and other unknowns as compared to the protected cocoon of an indoor laboratory. Like coral reefs, the canopy world was uncharted, so each element of research was more than simply a student exercise—it was a venture into the unknown. I probably spent half my time designing new methods and the other half doing the actual field research.
From my reading, I also learned that by the time I came on the scene in 1979, less than 10 percent of the country’s original rain forests remained. Governments like the one in Queensland were hell-bent on logging them for timber extraction, without any understanding of issues such as biodiversity, extinction, or restoration. Of the estimated ten million square kilometers (6.2 million square miles) of the world’s rain forest, less than one quarter of 1 percent existed in Australia (about 22,500 square kilometers, or 14,000 square miles), but it contained species found nowhere else on Earth. Less than 10 percent of that tiny percentage was safeguarded in national parks, so I felt a sense of urgency to explore those last remaining stands before they too disappeared.
I selected five tree species for long-term observations about leaf growth and death, a large-enough sample to ensure diverse patterns yet small enough for one arbornaut to manage. Each species was either representative of one of the major rain forest types and/or had an unusual foliage trait. They included:
Giant stinging tree (Dendrocnide excelsa), with extraordinary dense, sharp, stinging hairs on both leaf and petiole surfaces, which inspired my curiosity about their apparent defense armor to defy any hungry herbivore.
Red cedar (Toona ciliata), one of the few Australian rain forest trees exhibiting a deciduous leafing pattern, raising questions about whether its entirely different phenology had any survival advantages as compared to neighboring evergreen species.
Sassafras (Doryphora sassafras), the only tree species common to all Australian rain forest types, giving a chance to examine how its foliage adapted to different environments.
Coachwood (Ceratopetalum apetalum), with leaves that were elongated, smooth, and waxy, which was typical of most rain forest species, so it seemed important to study the “average leaf.”
Antarctic beech (Nothofagus moorei), which defied the conventional rules of rain forest tree diversity by growing in monodominant stands, leading me to wonder why insects didn’t overexploit such a homogeneous leaf supply.
I returned to my first coachwood for a pilot test of the field data collection methods and carefully enacted a protocol marking replicate leaves on three branches at three heights. I climbed to the first level of foliage, called the understory, which is deeply shaded and extends from zero to thirty feet high. I dropped a special, super-large forestry tape measure to record the exact vertical distance from the ground and repeated the same procedure for mid-canopy (ranging thirty to sixty feet high with intermittent sun flecks, small spots of sunlight streaming through the upper leaves), and then uppermost canopy, evident from the abundance of sunlight hitting the leaves (usually located above sixty feet). At each level, I selected three branches, each with five to fifteen leaves, and marked the first one by encircling it with an unobtrusive necklace of fishing line and yellow electrician tape labeled “Branch 1–1.” In a small yellow waterproof notebook, I transcribed the meaning of each label: branch number 1 and height 1 (for example, five yards). Each leaf was numbered, and represented data points at each height, so I could monitor changes throughout a leaf’s lifespan. I repeated this for branches numbered 2 and 3, also at the same height and light levels but simply replications.
The tricky part during the first climb of every tree was writing a legible number on all the leaves of each branch while dangling from a climbing rope. I had to avoid breaking a leaf when touching it or exerting undue pressure on a branch, even if wind swayed the rigging. The leaf at the base of each branch was numbered 1, and then 2 onward to the highest numbers toward the branch tip so I could continue the numbering sequence when new leaves emerged the following season. As with all plant growth, the new buds are at the tip of the branch, and so the new leaves emerge at the outermost region of the canopy. It required occasional acrobatics to reach along each branch from a swaying rope or sometimes flailing upside down in the harness to gently grasp the outermost leaves. I soon became adept at leaf marking and to this day have never broken a leaf or branch during many decades of treetop surveillance. But those first branches created great anxiety as I learned the nuances of how to make notes while dangling from a rope. One notable episode was my monthly visit to coachwood branch 2–2, situated in the mid-canopy of tree number 2, where I learned to push away from the tree trunk with my left foot, gently grab the branch with my left hand, and then lie almost horizontally in the harness to reach the newest leaves, which were growing farther away from the original rope transect.
During those first weeks of fieldwork, I bought a cheap orange mop bucket that became a mainstay, holding an ever-growing cadre of gadgets that had outgrown my waistbelt: waterproof Magic Markers, notebooks, pencils, rulers, graph paper, yellow electrician tape, tape measure, clippers, fishing line, acetate sheets (for tracing leaves), vials (for bugs), my all-time favorite pooter (a crazy sucking gadget that allows safe inhalation of a bug into a vial), camera, Oreos (always!), and water. I tied the bucket to a carabiner, which dangled from a clip on my waistbelt for easy access. I laid an inexpensive six-foot-square, ten-dollar tarp on the forest floor, to minimize mud on the ropes and field gear. We field scientists pride ourselves on ingenuity and an ability to make do. Lab scientists usually require expensive grants to purchase and maintain sophisticated machinery, but field science is typically conducted with relatively modest budgets and a few rough-hewn gadgets.
My fieldwork on that first tree took an entire day to rig ropes and number each leaf on three branches at three heights. It took two more days to do the same thing for trees 2 and 3. I created data sheets as the leaves were marked; each leaf had its own line and twenty-four months of blank squares set up to record monthly changes—herbivory, drying, color change, or death. Once satisfied with the methodology for this activity, I repeated the process for all five species to total three branches at three heights in three trees at three sites of three rain forest types, all within a day’s drive. Once the trees were rigged and their leaves marked at different heights, the monthly checks took much less time to revisit. I left nylon blind cords hanging in each tree, so it was easy to hoist the climbing rope into position every month. These slim cords were dark green, innocuous enough to remain invisible and not entangle any creatures. I bought several one-thousand-foot rolls of camouflaged cord, enough to leave in each rigged tree. Fortunately, no lines were ever yanked from a tree crotch. Every month, I inspected each leaf and devised coding to fit on the field data sheets. E stood for young/emerging; G for galls; Y for yellow; and other letters representing different ecological signatures, such as insect frass (aka poop), spider webbing, or presence of caterpillar gangs. Hugh, my loyal colleague from marine biology, volunteered as “dirt” on the ground to record data. Today, an electronic tablet could organize this type of work with far less effort, but we relied on old-fashioned pencils, waterproof paper, and the tedious process of transferring the data onto spreadsheets later. My brain was on overload during those first months of fieldwork and I was exhausted. Words could not express the level of excitement I felt at the forefront of discovery, and it was truly astounding that no one had ever studied the lifespan of an evergreen leaf in the rain forest canopy. Almost every month of sampling inspired a new piece of equipment or adjustment to do things more efficiently and safely.
During the second monthly visit, I was shocked to discover that many of my carefully numbered leaves had been partially eaten. Small holes, big holes, and even galls were evident on most foliage. I was quite affronted anything would dare to compromise those leaf samples, sometimes chewing directly through the ink numbers only recently inscribed. Herbivory emerged as a major factor threatening foliage survival, especially for new leaves. I became adept at recognizing different types of herbivory: chewing, which created outright holes in leaf tissue; mining, which comprised burrowed artistic tunnels between layers of leaf tissue; galls, which were small, swollen infection sites where insects had laid eggs; or fungal attack, which rendered black spots on the foliage. A young leaf is extremely vulnerable to herbivores not only due to soft, chewable tissue, but also because it is oftentimes more digestible before sequestering defensive chemicals. Plant and insects are engaged in an arms race—the plants trying to create foliage more resistant to successive generations of defoliators, while the insects rapidly adapting to digest them. Leaf survival strategies include toxins, toughness, and seasonality of leafing strategically adjusted to avoid insect emergence. Insect herbivores scramble to stay ahead of the leaf defenses, adapt to digest chemicals and chew tougher foliage, hatch out in time to consume new leaves, and overcome any other physical or seasonal mechanisms that plants might develop. For example, a tree that leafs out gradually over long periods of time can minimize onslaught by specific caterpillars that hatch synchronously. Equally important, an herbivore needs to find its foliage of choice amid a vast green expanse. In tropical forests, this includes thousands of different tree species with leaves that are soft versus tough, nutritious versus not, old versus young, common versus rare, already eaten versus still whole, protected by ants versus otherwise, sun versus shade, and high versus low. It occurred to me that the forest canopy was like the most complex salad bar on the planet. Just as humans select from various greens to create a salad, insect herbivores in the treetops confront an enormous choice of vegetarian fare, but only some of which they are adapted to digest. Beetles may fly many miles to find a coachwood tree with young leaves to suit their palate and jaw strength. Leafcutter ants (Atta sp.) in Costa Rica may forage several vertical miles up and down many trees to find a supply of a specific texture of Virola leaves for their thousands of workers to transport into underground fungal gardens. A specific weevil species may travel the entire length of a sassafras branch to find ideal sun-flecked conditions containing leaves with suitable texture so its proboscis can suck the leaf juices.
Another discovery during those initial climbs into the eighth continent was how leaves changed in size, color, and thickness at different heights. The vertical ascent in most trees was akin to a skyscraper where the penthouse differs significantly from the real estate in the basement—not just in terms of view, but of light, air quality, winds, and just about any other environmental factor. While climbing up the brown, snaky rope (at least to me it looked like a serpent coiling down through the leaf layers), I first encountered understory leaves at lower heights growing in conditions of shade, no wind, and high humidity. Those lower leaves usually slapped me in the face as I climbed because they were large, floppy, and thin. Dark green in color, they were speckled with insect holes and etched with circular, artistic trails of leaf miners. Sometimes the leaves were dirty with pollen or coated by dust due to the absence of high winds or pelting raindrops. Often, they were covered with a layer of moss, lichen, and other miniature biodiversity, things that thrived in the deep shade on a moist leaf surface. This layer of life upon a leaf was collectively called epiphylly, which is a veritable commune of Lilliputian creatures, all living on one phylloplane (a fancy word for the surface of a leaf), and to date only two scientists have dedicated their careers to study it.
