Consequences of seasonal snow cover for carbon cycling of world forests: direct and legacy effects

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Forests are host to much of the world's biodiversity, and also provide many benefits to society, including the provisioning of clean air and water, opportunities for recreational activities such as hiking and the acquisition of valuable resources including timber and medicines. Forests also provide a less-appreciated benefit to humans through the cycling of carbon dioxide (CO2) between the air and the trees. As humans add CO2 to the air through the combustion of fossil fuels for energy, the amount of carbon in the atmosphere accumulates. This extra CO2 in the air alters the natural greenhouse effect, and is changing temperature and weather conditions across the planet. Part of the CO2 added to the air by human activities remains in the atmosphere, while some of it is absorbed by the oceans and land, especially by our vast forests. As a result, forests currently provide an important mitigating effect for climate change, slowing the rate of change. Seasonally snow-covered forests cover a large amount of land around the world, storing carbon in both the trees and soils. However, these areas are being modified by changing climate conditions and it is unclear how changes in snowpack will affect the ability of forests to store carbon. This project will investigate the unique influence of the snowpack on carbon cycling by using data collected across the northern hemisphere at research flux tower sites. The results of this project will advance scientific understanding of snow and tree interactions and will also be shared with the public through many activities at the Natural History Museum of Utah, allowing visitors to engage with and ask questions about the project. Forests play a critical role in the global carbon cycle, exchanging large quantities of carbon with the atmosphere. World ecosystems release an order of magnitude more CO2 to the atmosphere via respiration on an annual basis than humans do via combustion of fossil fuels and land use change. However, forests remove just a bit more CO2 via photosynthesis than they release via respiration, and the annual net uptake of CO2 by land ecosystems is smaller than the human CO2 production. This provides an important mitigating benefit to the rate of atmospheric CO2 increase and associated climate change. However, there are many uncertainties about forest carbon cycling that prevent robust forecasts of ecological processes into the future. This project will provide mechanistic insight into carbon cycling in snow-covered forests worldwide. The project will investigate the role of snowpack in forest carbon cycling to uncover the mechanisms behind both direct biophysical and indirect controls that reflect cross-season biophysical and biogeochemical legacies. Nearly 600 site years of carbon cycle data at over 60 unique seasonally snow-covered forests available from the worldwide FLUXNET and Fluxnet-Canada flux tower networks will be used. These sites represent a broad range of climate conditions and will provide fundamental information on the controls of snow-mediated carbon cycle processes across seasonally snow-covered forests globally. This information is crucial for the advancement of terrestrial biosphere models, improving our understanding of carbon flux response in seasonally snow-covered ecosystems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.