Satellite assessments of recovery from climate stresses must be backed up by on-the-ground data, researchers argue

Tracking how landscapes recover from droughts and wildfires with satellite observations alone risks misunderstanding their response to these climate stresses, according to a new study.

The method - known as remote sensing - measures electromagnetic signals from orbit.

Scientists rely on these signals in combination with models and other assumptions to understand what’s happening on the surface below.

Instead, much stronger links between remote sensing and field ecology are needed, according to an international team of researchers led by the University of Connecticut and supported by Cardiff University.

Their studytests how effectively one of these top-down satellite observation strategies, known as Temporal Autocorrelation (TAC), captures the drought status and physiological state of trees.

Their findings, published in the journal Nature Ecology & Evolution, begin to uncover the ecophysiological mechanisms of trees which underly TAC as an ecosystem resilience metric.

Dr Paulo Bittencourt, one of the paper’s co-authors based at Cardiff University, said: “In recent years, remote sensing has become an increasingly powerful and widely used tool for monitoring our planet. However, its growing popularity has often come at the expense of understanding the biological mechanisms operating at the scale of the individual organisms and ecosystems on the ground. Not only that, but existing remote sensing metrics have also not yet been rigorously tested or validated.

“In this work, we used an Amazon-wide plant hydraulics dataset that I developed with colleagues over the past decade to test the mechanisms underlying remotely sensed ecosystem resilience metrics.”

The researchers used data from 114 tree species and more than 342 individual trees across nine Amazon forest plots to assess how close they were to suffering damage from lack of water.

They compared these data with satellite observations of changes in forest vegetation over time.

The satellite-based estimates of forest recovery speed matched on-the-ground measurements of how well trees can withstand drought.

“Our study demonstrates the need for a much closer integration between the broad observational capacity of remote sensing and the mechanistic understanding provided by field ecology,” explains Dr Bittencourt, a Tropical Plant Ecologist based in Cardiff University’s School of Earth and Environmental Sciences.

Despite their results, bridging the gap between remotely sensed observations and the physiology of individual trees in the field remains a major challenge, according to the team.

They say much more field-based research is needed to test the key assumptions about how trees, and life in general, function.

“Only then can we ensure that the wealth of remotely sensed data available, together with the powerful analytical and AI tools used to analyse them, reliably reflects the conditions that ecosystems are actually experiencing,” added Dr Bittencourt.

Their paper, ‘Physiological fidelity of a satellite-derived forest resilience indicator in the Amazon,’ is published in the journal Nature Ecology & Evolution.