Cloud forests
Iwas sitting on the patio of the Cafe Caburé looking across a dirt road into the densely forested Bajo del Tigre Reserve. A car drove by, kicking up a dust cloud. These are not the clouds you look for in the damp, verdant cloud forests of Monteverde, Costa Rica. But it had been a really dry year.
A gust of wind traveled upslope toward the cafe, and the brown cloud dissipated. I reached for my sweatshirt. Although this was the tropics, I was 4,600 feet up the mountain. The air was comfortably cool.
Then a clear, metallic call cut through the wind. A Froot Loops-colored beak protruded from the tree line. Tourists and birders jumped out of their chairs, eyes pressed to their binoculars. “Look! To the left, it’s the keel-billed toucan. Can you see it?” I heard the shouts but was focused on something else: the shocked and distressed faces of locals and other scientists like myself. The toucan was not supposed to be there. For the last decade, I have made regular visits to Monteverde to study the soil in the surrounding cloud forest, situated on the Pacific side of the Cordillera de Tilarán.
Clouds have a significant effect on what happens high up in the mountains. Less sunlight hits these forests, and in the cooler, wetter conditions that prevail, processes like decomposition operate at a slower pace than in lowland rain forests. These forests are packed with species found nowhere else.
But things are changing in Monteverde. The cloud layer is moving up the mountain. Warmer temperatures in the lowlands are causing clouds to form higher up than they should, and the forests that were once enveloped in these mists now suffer long dry spells. This is affecting not only the animals and plants, but also the soils I study. As the damp ground dries, dead plants break down faster, releasing carbon dioxide into the atmosphere.
In these changing situations, species either adapt, move or die. That’s why the keel-billed toucan we saw was so high on the mountain. The toucan was moving up as the climate below warmed.
Of course, this is a problem not just in Costa Rica. Uphill migrations are happening throughout the tropics right now. Tropical plants and animals tend to tolerate only very narrow temperature ranges. Small deviations are a big deal. So mountains can provide temporary relief for lowland species as temperatures warm. That is, until they get to the top and there is nowhere else to go.
This can lead to local extinctions, as species vanish from certain areas. And although these local extinctions do not always lead to global eradication, they do give us a good indication of how a species might fare overall in the future.
We don’t just have studies that indicate such movement is taking place; you can see it happening, even during a meal on a patio.
My interrupted lunch was three years ago. Now the keel-billed toucan hangs out 460 feet higher up the mountain. There are only 1,000 more feet to the top. Caitlin Looby is a Ph.D. candidate in ecology and evolutionary biology at the University of California, Irvine.