Susan Letcher, Purchase College (SUNY)
Leigh, Mareike, and I have been out in the rain forest measuring trees for 5-6 days a week since June. We just finished data collection; now comes the analysis and writing. Since not many people get the chance to experience life as a tropical forest researcher, I decided to use this space to describe Thursday last week, a typical day in the field—the highs, the lows, the odd details that we’ve begun to take for granted.
5:15 am: The howler monkeys are roaring in the trees and the buff-rumped warblers along the riverbank have commenced their ear-splitting morning chorus. As the sky lightens outside, we dress in our field clothes and boots and walk through the jungle towards the comedor (dining hall), pausing on the suspension bridge to check for caimans on the bank and green ibises in the trees.
6:30 am: Another cup of coffee to wash down the fruit, eggs, and gallo pinto (a traditional Costa Rican breakfast dish of rice and beans fried with cilantro and diced onions). Rice and beans for breakfast is a decidedly acquired taste, but fortunately both of my students have picked it up. We linger around the breakfast table sharing adventure stories and jokes with other researchers. Carlos de la Rosa, the station director, points out that we’ve already broken the La Selva rainfall record for the month of July.
7:30 am: We’ve picked up our sack lunches, field gear, and a radio. Leigh goes to the sign-out board to record our planned location; Mareike is putting little X’s of medical tape on her heels to prevent blisters. I fill up my water bottles and accommodate the gear in my pack so that the meter tape won’t dig into my back as we hike. Just as we leave, as usual, it starts to rain.
9:04 am: We’ve reached our destination, CC 1750. La Selva trails are marked every 50 meters with numbered posts. The CC (Camino Central) is a muddy, hilly trail that bisects the eastern half of the reserve. Close to the station buildings the trails are paved with concrete for bike access, but this far out—1100 meters on the CCL and an additional 1750 meters on the CC—there’s not a lot of infrastructure. The trails consist of a muddy slash where the understory has been cleared away, often doubling as streambeds when the rain gets heavy.
We take out the data sheets that show the location of our trees. Both of my students are using long-term data from the TREES project, an NSF-funded investigation of how trees grow and reach the canopy. In temperate forests, it’s possible to take a core from a tree and examine annual growth rings. In tropical wet forests, where trees keep their leaves year round, there’s no annual growth cessation to produce rings. So the only way to really understand how fast trees are growing is to go out and measure them directly. The TREES project was founded in 1983 by Deborah and David Clark. Every year, expert technicians measure a set of approximately 2000 trees, ranging in size from knee-high seedlings to giant emergent trees that loom over the rest of the forest, of ten different species. I became involved in TREES in 2011, and every summer since 2012 I’ve had students working on associated projects. This summer, Leigh is measuring the amount of lianas (woody vines) on fast-growing tree species and Mareike is investigating the trees growing in the neighborhoods of four seedling species to examine whether the relatedness of neighbors affects seedling growth and survival.
9:06 am: After a water break, we take out our compasses and locate our first tree, 60 meters away at a bearing of 120°. Rather than a plot-based survey, the TREES project relies on an inventory of individuals scattered across 250 hectares (about 625 acres) of old-growth forest, and the trees are referenced to one another with a series of compass bearings and distances.
The tree we’re aiming for is a giant, stately, white-barked Balizia elegans, an emergent tree that spreads its great arms out above the rest of the forest canopy. The trunk glimmers like a beacon through the dark understory and layers of dripping leaves. As we approach, its true size becomes apparent: the trunk is well over a meter in diameter, and the tallest branches are probably 40 meters high—about the height of the space shuttle. A series of other compass bearings and distances leads us to a shaggy-barked Minquartia guianensis with a fluted hollow trunk where we can hear bats chirping inside, and then to our ultimate target, a feathery-leaved seedling of Pentaclethra macroloba.
We lay out a set of four 10 meter-long tapes from the central point and measure the diameter of all the trees falling into our circular plot. I squint up into the canopy to identify them. For some of the less-evident trees, I make a tiny scratch on the trunk to look for sap and test the odor. Hernandia didymantha has a heavy medicinal smell; Dendropanax arboreus smells like carrots; the genus Protium smells like incense; the Lauraceae vary from sweetly cinnamon-scented to a sharp chemical odor like asphalt on a hot summer night. In my now 11 years of work in this region, I’ve learned to recognize most of the trees. For the ones I’m not sure about, we pick up some fallen leaves and make notes in the data book.
11:15 am: We find a fallen log that looks like a good resting place. After checking that it’s not a thoroughfare for ants, Leigh and Mareike spread out a poncho and I sit on the plastic bag that keeps the data sheets dry. We chow down on sandwiches, cookies, and plantain chips.
12:30 pm: The next tree on our data sheet is across the Salto, a stream that runs down the middle of La Selva. In ordinary years it’s a rock-hop to the other side, but with the record rains this July it’s a rushing mud-brown torrent at least two meters deep. We confer. Luckily, there’s a fallen tree not far downstream that looks like it will convey us safely across. I go first: if it supports my weight, it will definitely hold up for my students. As I cross, I clear away the spiny vines that cling to some of the branches. The log bobs up and down disconcertingly and there’s one stomach-dropping moment when I look down to the rushing water below, but it holds up and there’s a good access point on the other side. Leigh and Mareike make their way across, and we search for a way up the muddy hill in front of us.
1 pm: A series of compass bearings leads us to one of Leigh’s liana trees. It’s a pink-barked, glossy-leaved Simarouba amara. As a fast-growing tree species, Simarouba generally avoids lianas. Not this one, though: its canopy is overshadowed by a dense mat of liana branches and leaves. One thick stem wraps around the trunk, and others hang down from the canopy. We measure the diameters of all the lianas at 1.3 meters from their rooting points—not always easy to determine, for a liana—and we walk around the Simarouba tree peering up at the canopy to assess the percentage covered up by lianas.
2:15 pm: We make our way back to the river and across the log, pausing only to take some photos. The long, muddy trail is calling, with showers and coffee waiting at the other end.
6:00 pm: Dinner at La Selva—the comedor fills up with the sounds of happy researchers returning from a wet day in the field. We load up our plates with rice, beans, vegetables, chicken for the meat-eaters and some sort of soy concoction for vegetarians like me. As the rain picks up outside and distant lightning flashes illuminate the clearing, we share jokes and stories and speculate on how much rain we’ll get tonight. There’s also talk of graduate school, experimental design, biostatistics, and taxonomy, and most of all there’s practical advice for building a life in the sciences. Many of the conversations in that comedor have guided me through my career. Looking around the table, I can tell that the students are picking up much more than they came for. When they leave here this summer, they’ll know more about themselves. They’ve pushed the boundaries of their comfort zones, whether it’s crossing jungle rivers on fallen logs, handling spiders and bats, or struggling with new methods of analysis they’d never heard of before the program. Most of all, they know what field biology is like and why we do it.
9:20 pm: We’re gathered on the back porch of the lab with several guitars, singing old favorites in English and Spanish. Someone’s come up with a new variant of “Let It Be:”
I wake up to the howler monkeys singing serenades for me,
$%%&! I think it’s gonna rain on me.
And though it may be cloudy now the monkeys’ song is telling me
Pretty soon it’s gonna rain on me.
Rain on me, rain on me, rain on me, rain on me…
$%%&! I think it’s gonna rain on me.
A friend once described La Selva as “summer camp for jungle nerds.” There is definitely a summer camp feeling to our time here—the endless days out in the woods, the silly in-jokes that develop, the nights singing along to someone’s guitar. The nerd part is more important, though. There’s a powerful spirit that develops in a place where everyone is fascinated by knowledge and lets that enthusiasm shine. Along with scientific papers, La Selva’s main export is the joy that comes from building an understanding of the natural world. When our students go back to the “real world,” they’ll carry it with them.