摘要：Recent field experiments in tundra ecosystems describe how increased shrub cover reduces
winter albedo, and how subsequent changes in surface net radiation lead to altered rates of
snowmelt. These findings imply that tundra vegetation change will alter regional energy
budgets, but to date the effects have not been documented at regional or greater scales.
Using satellite observations and a pan-Arctic vegetation map, we examined the effects of
shrub vegetation on albedo across the terrestrial Arctic. We included vegetation classes
dominated by low shrubs, dwarf shrubs, tussock-dominated graminoid tundra, and
non-tussock graminoid tundra. Each class was further stratified by bioclimate subzones.
Low-shrub tundra had higher normalized difference vegetation index values and earlier
albedo decline in spring than dwarf-shrub tundra, but for tussock tundra, spring albedo
declined earlier than for low-shrub tundra. Our results illustrate how relatively
small changes in vegetation properties result in differences in albedo dynamics,
regardless of shrub growth, that may lead to differences in net radiation upwards of
50 W m − 2 at weekly time scales. Further, our findings imply that changes to the terrestrial Arctic
energy budget during this important seasonal transition are under way regardless of
whether recent satellite observed productivity trends are the result of shrub expansion. We
conclude that a better understanding of changes in vegetation productivity and distribution
in Arctic tundra is essential for accurately quantifying and predicting carbon and energy
fluxes and associated climate feedbacks.
