Collecting three leaves

Sometimes ecologists don’t look like they’re working very hard. I had a day where the major accomplishment was collecting three leaves from the forest. But what if I told you that each leaf was thirty-four feet long? The scourge of our research project is the giant Attalea butyracea. We are measuring the average area of leaves for all the dominant species in our transects, and the American oil palm happens to be one of them.

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Palms are evolutionarily very strange. They don’t develop wood in the same way as other species, relying instead on a diffuse growth of fibrous tissue to provide structural support (think of them as grasses gone bad). The woody structures you see above are actually enlarged leaf petioles, the usually flimsy bases of leaves that attach them to stems. The things that look like leaves are actually evolutionary equivalent to leaflets (pinnae) like you might see on a mesquite or ash tree.

The consequence of this evolutionary biology digression is simple: when we measure leaf area, we can’t just collect a single pinna and declare victory. We have to cut down the entire leaf and carry it back to our lab without damaging it. This is a bigger challenge than it appears. You may have seen landscaping crews trimming palm trees in parks – but they use mechanized lifts and power tools, and have complete freedom of movement because of roads. We have to hike all our equipment in and out, and often can’t see where we are cutting because of other trees and vines. These leaves weigh dozens of pounds, have sharp edges, and fall from thirty or forty feet in the air. How do we do it without getting hurt, and why does it take all day to collect three?

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We use a chain saw to cut the leaves out of the canopy, like the one you see here. The main challenge is getting the saw blades on top of the leaf. To solve this problem, we attach the saw to a rope, the rope to a bean bag, and the bean bag to a long extensible metal pole. We then carefully raise the bag up into the canopy, get it stuck a few times, and eventually maneuver it over the leaf. Then with some more pole work we pull the bean bag down, and are ready to start cutting.

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Cutting too hastily is a bad idea. Imagine a thirty-foot long heavy sharp stick crashing out of the sky, and imagine all the other things it might bring down with it. Sometimes the falling leaves catch on other trees and abruptly swing in another direction, which can be an unwelcome surprise for the field crew.

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Once we’ve found a safe location, we use two people to pull on the saw, and wait for the loud cracking sound that indicates the triumph of gravity over leaf. The leaf is now on the ground, but we’re far from finished. We have to bring it home without damaging it. This leaf we cut more than two kilometers away from our laboratory, and the forest is full of trees and vines that make it difficult to navigate with a heavy object of this side.

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Extra care needs to be taken before moving a leaf too far. There are some arboreal spiders that call the pinnae home, and they make unwelcome guests when a leaf is wrapped in one’s arms. This one was loathe to leave its home, but quickly found its way to another nearby tree once we had carefully dislodged it with a (very long) stick.

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After the brief spider inspection, we begin the long and sweaty task of dragging each leaf home. This was the first time I ever had to make a K-turn outside of a vehicle!

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Once we get the leaves back, we have to measure leaf area, which was the original goal of the entire adventure. The leaves are far too large to scan using normal office equipment, so we resort to taking photographs of leaf sections. Here you can see us removing pinnae (more than 200 in total) and placing them on a white background – a shower curtain – for photography with a scale bar.

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Each leaf took up to sixteen photographs to completely image, and involves several other scientists gawking at our slow progress.

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By sunset, we were able to finish three leaves, from start to finish. I don’t think any of us much like palms, but I hope you see how much work it takes to measure them.

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