Spring is “springing” earlier now than in years past. Today’s early growing season green-up may arrive several days earlier than it did 20 years ago, and many researchers believe global warming is to blame.

Professor Tom Gower and scientist Douglas Ahl, both with the Department of Forest Ecology and Management at the UW-Madison’s College of Agricultural and Life Sciences, want to test that hypothesis in northern latitudes, where global warming is expected to have the biggest impact. The study, funded by NASA, will advance Gower’s long-term effort to systematically link field measurements, remote sensing, and ecosystem modeling to quantify the effects of global change on the carbon budget of boreal forests.

Although studies show global warming is likely affecting boreal forests, Gower and Ahl are not certain that it is the only factor contributing to the early-greening trend. They believe forest disturbance, especially wildfire, also plays a role.

Fire has always played an important part in the boreal forest ecosystem. It recycles biomass and nutrients, helps to maintain a diverse landscape of different vegetation ages and types, destroys dead or dying trees, and keeps forest pests in check. Some boreal tree species, including jack pine, require fire to reproduce.

Fire frequency in northern Manitoba and Saskatchewan boreal forests has increased by 200% or more in the last 20 years. Gower and Ahl believe that the corresponding earlier green-up may be more than just coincidence.

They headed to Canada in early June to establish their study sites. Gower and Ahl will measure vegetation in eight stands near Thompson, Manitoba, ranging from old growth black spruce stands to very young stands that originated from high intensity fires that reset succession.

They plan to set up light sensors in each stand, measure how much light is absorbed by the canopy, which can be used to quantify the phenology of the forest, and compare these data to MODIS satellite data. Gower and Ahl expect to begin receiving information in a few weeks, and will monitor the stands for two field seasons.

Data will show whether MODIS can accurately measure early growing season green-up and/or changes in vegetation composition following disturbance, and whether global warming is the primary cause for the early green-up.