As Earth warms, satellite images send strong indications of Arctic greening. But a greening signal belies greater complexity. Climate change brings a ground war to the tundra as plants compete for dominance. In many tundra regions, taller shrubs are invading areas once bare — or with short cover — from like plants like lichen. Understanding Arctic vegetation change is vital to understanding carbon storage and feedback mechanisms to help improve climate change models.
But revealing granular details is challenging in an environment that is remote, difficult to access and sparsely populated. For decades, remote sensing has provided Arctic eyes in the sky, but with drawbacks. Ecologists are challenged with trying to extrapolate fine-scale patterns from coarsely grained satellite observations. Emerging research suggests drones could help bridge mismatches of scale.
Much of the evidence for Arctic greening comes from data from satellites orbiting Earth since the 1970s. Satellite data provide coarse-scale resolution. Pixel sizes can correspond to areas as large as 24 square miles (64 square kilometers), explains vegetation ecologist Isla Myers-Smith at the University of Edinburgh.
In contrast, for nearly two decades at Qikiqtaruk in Canada's Yukon Territory, Myers-Smith's research team has quantified Arctic vegetation change in square-meter plots about the size of a coffee table. Year after year, her team dropped 100 pins in each plot, recording every plant, leaf and stem the pins contact. It's painstaking work. Assessing each square takes hours.
But the tundra is vast. Only tiny Arctic fragments can be examined in such detail. The overall greening signal provided by satellites — the normalized difference vegetation index (NDVI) — is unmistakable, but are plants growing bigger? Are different plants encroaching? Are changes homogeneous? These questions intrigue tundra ecologists wanting to know what's happening on the ground.
It's difficult to scale from square-meter plots to what satellites see over large spatial extents. "You end up with that gap in between," says Andrew Cunliffe, research fellow at the University of Exeter in the United Kingdom. He led a recent study addressing this gap, published in Environmental Research Letters. Coauthored with Myers-Smith and three others, the study represents a broader effort to bridge scale gaps using drones.