the Sky Islands of the Andes
Walk through the soaring peaks of the tropical alpine. In this world
of wild extremes, it is summer by day, and winter by night.
By Holly McKelvey. Photographs by Daniela Martínez Medina
Summer, in the temperate latitudes, slides out from under heavy snow through the muddy blossoming of spring, and slips into the humid hum of pollinators amidst leaf-laden branches. Between the tropics and the poles, summer unfurls in a wash of warmth, often in stark contrast to the winter months before.
But some parts of the world do not adhere to this seasonal template. As we move towards the equator, Earth's axial tilt holds less and less sway over seasonal change, blurring December into May into August without a wrinkle. But the tropics do have their own wild extremes that echo the winter/summer dynamic: at elevation, temperatures can fluctuate as dramatically as any seasonal change.
This is the tropical alpine: the rolling grasslands between treeline and snowline in the high mountains of the tropics. In the northern curve of the South America Andes, this region is called the páramo. As we walk through these rich ecosystems, we place our feet gently amid the hummocks of cushion plants and knots of browning grasses: these plants are the páramo's adaptations to wild extremes.
By day, the páramo is gentle. On an inviting summer afternoon, temperatures reach into the mid-80s (30°C). Warmth radiates down from the tropical sun overhead and up from the peaty soils below.
But night paints a different story. Temperatures plummet below freezing; frost gathers on exposed surfaces, and the water captured in soil or plants freezes and expands, ripping apart roots and breaking up the delicate cellular structure inside the plants' leaves.
And then, abruptly, after a brief but brutal six hours of sub-freezing nighttime winter, the páramo and its plants are plunged back into the warm and gentle day. The hot tropical sun rises, the frost melts, and summer begins again. Rinse. Repeat.
Summer by day, winter by night. In this world, plants survive only if they are braced for extremes.
The plants adapted to this harsh environment survive through insulating layers that help them stay warm at night. This insulation? Their own dead material. Like coral reefs, mound-like cushions of plants grow layer upon layer on top of themselves, creating great peaty hummocks with old plant material contained inside, which slowly decomposes. This process of decomposition generates that same heat you feel if you thrust your hand into the center of a compost pile. This heat is what keeps the overlying youngest layer alive during the harsh night.
Gray-green grasses, clumped together, keep their dead material aboveground, and closely gathered around their living blades of grass; over half of the blades in a single clump might be dead, but their proximity to the living blades creates a protective insulation.
What's more, in this region where extreme temperatures provide such a harsh limitation to growth, plants are remarkably non-competitive. The hummocky cushion plants are composed of multiple species cohabiting the same mound, keeping their neighbors alive as much as themselves as they grow outward layer by layer. In these harsh conditions, cooperation is a far safer option than competition.
The elegant cooperative nature of these highland species is echoed in the daytime tranquility of this ecosystem. Walking through it is to walk through another world, one perched high in the Andes, an island in the clouds
Dani is a Colombian biologist and bat-lover, pursuing a Masters in Applied Ecology at the University of Kiel, Germany. She loves to find hidden details in the world around her through her camera lens, and her jokes in English are just as funny as her jokes in Spanish. Reach her at firstname.lastname@example.org
Holly is a graduate student in Environmental Management at the University of Kiel, Germany, where she cycles a lot, drinks tea, and enjoys the brief lapses of sunshine. She can be reached at email@example.com