A Pulsating Palette
Over the course of millennia, white snow cover, vibrant autumn foliage and bright bursts of green have punctuated the rhythmic cycles of winter frosts, spring showers and long, warm summer days. Animals have evolved to be in sync with seasonal change: They bring young into the world just as nutritious green sprouts emerge in spring, and molt to blend in with winter whites and summer green-browns. It’s an intricate dance scientists refer to as phenology.
Richardson’s efforts to decipher this color code began in the 1990s, shortly after his return from an eight-month trek in Canada’s Yukon Territory. “It was the vegetation, the transition from forest to tundra and how the colors changed through the seasons that really captivated me,” he recalls. Richardson had recently abandoned pursuit of a Ph.D. in economics at MIT and found himself in awe of nature’s colorful clockwork — so much so that he redirected his studies.
Richardson enrolled in Yale University’s forestry program in 1996 and a few years later threw himself into a project lopping off balsam fir and red spruce branches in the White Mountains. He measured how much light the needles reflected in different wavelengths. This is an indicator of stress and “a very precise way of measuring color,” he explains.
Richardson showed that needles in the harsh, resource-poor high altitudes invested in stress-protection pigments to cope with wind, cold and blazing sun.
Reading the Leaves
“Phenology is really sensitive to weather,” Richardson explains. “If it’s a cold spring, leaves will come out later. If it’s a warm spring, that will happen earlier.”
Forests in the United States absorb and store more than 750 million metric tons of carbon dioxide each year, or more than 10 percent of national carbon emissions. Warmer temperatures triggering earlier green sprouts could produce a longer growing season in some places and more photosynthesis — and thus more carbon uptake. But early growth followed by frost or drought could damage fragile sprouts and reduce the amount of carbon that certain plants are able to absorb. Some species also respond to warming by fast-forwarding through their life cycles, narrowing the window for photosynthesis and carbon uptake.
Nature’s color palette already shows effects of climate change. Along the East Coast, where the “green wave” of spring leaves sprouting from maples, oaks and poplars historically has rolled from Miami to Maine in 75 days, atmospheric scientists with Princeton University predict the wave could take just 59 days by the end of the century. In parts of New England, fall colors arrive a few days later than they did 20 years ago, and the reds are more muted as autumn temperatures in the region warm.
But scientists don’t know what new rhythms will arise across different regions — whether bursts of green will be brighter but shorter-lasting, for example, or more muted but longer-lasting. Nor do they know what such changes mean for the food web; for life-cycle events like migration, breeding and nesting; for the amount of moisture that trees will suck from the soil; or for the amount of carbon dioxide stored by plants.
That’s what Richardson hopes to tease out. “As we build up a big archive — warm years, cold years, wet years and dry years — we can use the data to develop models of how weather and phenology are related,” he says. These models can then be mapped against climate forecasts to predict how phenology could shift in the future, painting a picture of landscapes in a world of warmer temperatures, altered precipitation and humidity, and changes in cloud cover. “We want to use phenology as a biological indicator of the impacts of climate change on ecosystems,” Richardson says.