Detecting long-term canopy change and vegetation shifts in northern peatlands using LAI and climate data

Northern peatlands store vast amounts of carbon, part of which might be released to the atmosphere as climate warming alters peatland canopies. To track these changes, we analysed recent greening and browning across northern peatlands, defined here as increases and decreases in leaf area index (LAI), from 2001 to 2023. We assessed vegetation change using gap-filled, sensor-independent LAI climate data record at 500 m resolution across the peatland-dominated pixels north of 45° N, defined as pixels with at least 90 % mapped peatland cover and no detected wildfire during 2001–2023. To our knowledge, our results provide the first multi-decadal assessment of peatland canopy change based strictly on mapped peatlands rather than on the broader Arctic and boreal domain in which peatlands are usually embedded. Although greening was widespread at the pixel level (77 % of studied peatlands; greening-to-browning ratio 3.5:1), the area-weighted LAI trend at the map scale was not significant. LAI anomalies were weakly positively correlated with air temperature and weakly negatively correlated with precipitation; multi-year mean annual precipitation, rather than air temperature, was retained in the model of long-term LAI trends. Higher tree cover was associated with less greening, but this association was weaker in peatlands with deciduous needleleaf cover and where precipitation was higher. Most peatland pixels showed a linear LAI trend with no breakpoints; where non-linear trends occurred, their breakpoints were often temporally aligned with phase shifts in the Pacific Decadal Oscillation. These non-linear trends differed by region: trends in which LAI first decreased and then increased were concentrated in West Siberia, whereas trends in which LAI first increased and then decreased were widespread across Europe, northeastern Asia, and Canada. Protected peatlands did not show different LAI trends once differences in climate and canopy were accounted for. Overall, recent peatland canopy change was not a uniform increase in greenness but rather reflected moisture-sensitive, tree-composition-dependent responses modulated by decadal climate variability.