Changes at Walden Pond

“It is astonishing how soon and unexpectedly flowers appear, when the fields are scarcely tinged with green. Yesterday, for instance, you observed only the radical leaves of some plants; to-day you pluck a flower.”  -- Henry David Thoreau

Henry David Thoreau, 1856. Credit: Photo courtesy of The Thoreau Society Collection at the Thoreau Institute at Walden Woods
Henry David Thoreau, 1856. Photo courtesy of The Thoreau Society Collection at the Thoreau Institute at Walden Woods

Great Meadows National Wildlife Refuge is located in Concord, Massachusetts. The area was home to a dedicated naturalist in the mid-1800s. He built himself a house on 14 acres of woods on the bank of Walden Pond. He dutifully and diligently recorded the flowering times of hundreds of plants as well as the behavior of rabbits, red squirrels, mice, birds and other animals for six years.

His name was Henry David Thoreau.

Thoreau provided an extensive array of data that has proven invaluable as a baseline for phenological research that continues today. Phenology is the study of events in nature that are influenced by climate and seasonal change.

A study conducted by Abraham J. Miller-Rushing and Richard B. Primack found that climate change is causing many plants to flower much earlier today than they did in the past. The two researchers used Thoreau’s observations, as well as the work of Alfred Hosmer, another naturalist who studied the ecosystem around Concord, as a comparison to their own modern-day observations. Their research concludes that in Concord, plants are now flowering seven days earlier on average than they did in Thoreau’s time.

But not all plants are equally impacted by climate changes. Some species have the ability to track seasonal temperature change and will flower earlier when temperatures are warmer. Other species don’t track temperatures as well, and will continue to flower at the same time every year—regardless of temperature variations. The ones that don’t track temperatures as well are more likely to suffer a decline in numbers; they also tend to be related to one another, so entire plant families are impacted.

Unfortunately, research also suggests that non-native species may be the ones that adapt the best to climate changes. A study conducted in Thoreau’s woods shows that non-native plant species are far better able to respond to recent climate change by adjusting their flowering time. The researchers discovered that mayweed chamomile (Anthemis cotula L.), which is native to the Mediterranean, shifted its flowering time over the years and now blooms 23 days earlier than it did in 1900.

The impact of thriving non-native species can be devastating to the environment. Non-native plants that propagate and become invasive can have tremendous negative impacts—both ecologically and economically.  An estimated 5,000 alien plants exist in the United States, displacing native species. One example is the European purple loosestrife. It has been spreading at a rate of 115,000 ha/year and has been blamed for reducing the biomass of 44 native plants and endangered wildlife, including bog turtles and several species of ducks that depend on the native plants. Loosestrife now occurs in 48 states and costs $45 million per year in control costs and forage losses.

New England aster at Great Bay National Wildlife Refuge. Credit: Greg Thompson/USFWS
Butterfly on a New England aster at Great Bay National Wildlife Refuge. Credit: Greg Thompson/USFWS

As climate change affects plants, it also affects the rest of the ecosystem, including:

In nature, timing is everything. It can influence recreation, agriculture—even economics. Whether people come to see the fall colors, watch migrating whales or catch a glimpse of rare birds, visitors to the Northeast impact the economy to the tune of millions of dollars. As the timing of nature’s events change, so will the timing of the tourist seasons.

“It matters if a plant changes flowering by even one day,” said Miller-Rushing, one of the country’s top phenology researchers, now with the National Park Service. “How it changes is relative to what it is dependent on. If pollinators are late or water isn’t available, that has a real impact. Small changes can fundamentally change an ecosystem.” 

Citizen Scientists

A “budding” scientist examines a blooming azalea in her front yard Credit: Photo courtesy of Frank Wolff
A “budding” scientist examines a blooming azalea in her front yard  Credit: Photo courtesy of Frank Wolff

There is an ongoing effort to share phenological data from around the world through the USA National Phenology Network. The group has partnered with the U.S. Fish and Wildlife Service, The Wildlife Society and the U.S. Geological Survey to create a program that anyone from an amateur in their own backyard to a skilled scientist in the wild can collect data that can be shared, integrated and compared to data sets over time.

In addition, the U.S. Fish and Wildlife Service is a sponsor of Project BudBurst—a network of volunteers who collect data on the timing of leafing, flowering and fruiting of plants. The data they collect is shared with scientists across the country in an effort to learn more about how different species of plants respond climate changes.

It’s a great way for school groups, scout troops, backyard naturalists, ecologists, nature-lovers and others to provide valuable scientific data—even in their own backyard.

All the tools and information are available on the Project BudBurst website. 

Story by Frank Wolff, Wellons Communications

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