Biologists in Massachusetts are drawing on the work of Henry David Thoreau to study the effects of climate change on wildlife. The author of ‘Walden' left diaries with extensive notes on the biodiversity of the Concord area. Looking back through these diaries, scientists have been able to compare the wildlife of Concord with what it was 150 years ago.
Thoreau was many things - a thinker and philosopher, a school teacher, a caretaker, and even the inventor of an improved pencil. He is best remembered however, for his retreat into the woods in 1846, as an experiment in simple living. It was during this time that he took his meticulous notes of the environment, as he explored every inch of the countryside. "I cannot preserve my health and spirits," he once claimed, "unless I spend four hours a day at least, sauntering through the woods and over the hills and fields."
On these walks Thoreau made notes of what he came across. He wrote down the animals and birds he saw, made note of the first buds, flowers and fruits on all the plants, and when the leaves fell. He took the temperature of the lake, measured the thickness of the ice, and when it first appeared and finally melted. All these things were fascinating to Thoreau, the "living poetry" of the earth, as he called it. ‘Walden' is full of his poetic descriptions of the Concord wildlife, from the loon that "makes the woods ring with his wild laughter", or the red squirrel that darts and pauses "as if all the eyes in the universe were fixed on him."
Now his descriptions have come to the attention of scholars at Boston University and Harvard. Aside from his notoriously small and difficult handwriting, the diaries are a perfect record of plant and animal behaviour for hundreds of species over a two year period. It is an invaluable and unique resource, and also a compendium of what has been lost. Comparisons between Thoreau's record and current field notes reveal that a full 26% of Concord's species have vanished, and a further 36% are now so rare that their disappearance is almost inevitable. "Thoreau was the earliest person to keep detailed records of when plants flowered in the US" says Richard Primack from Boston University. "If you came out here looking for the flowers Thoreau saw, you wouldn't find many of them."
Since much of the area has been preserved, this loss of biodiversity cannot be attributed entirely to development or habitat loss. Mean temperatures in the area have risen 2.4 degrees Celsius (4.3F) over past decades, making climate change an important factor. As temperatures have changed, plants have either adapted or died off. To keep up with the changing seasons, wild flowers are now blooming a week earlier, or in some cases even three weeks earlier, than in Thoreau's day.
These changing blooming times are crucial to species adaptation to climate change. One of the key findings of the studies is that the plants that have disappeared are the ones that have not been able to change their blooming times. Orchids, buttercups, roses, violets and lilies have all been unsuccessful at adapting, emerging too late in a changing springtime, and going out of synch with pollinators. "It had been thought that climate change would result in uniform shifts across plant species," says Harvard's Charles C. Davis. "Our work shows that plant species do not respond to climate change uniformly or randomly. Some plants around Walden Pond have been quite resilient in the face of climate change, while others have fared far worse."
After examining wild flowers, other groups are analyzing Thoreau's observations on birds, marshalling local bird-watching groups to help out - a collaboration between nature lovers present and past. As this NPR report concludes, Thoreau would probably be pleased that his notes have proved so useful to science. What he would think of the species loss is another matter altogether.
