163 years ago, Henry David Thoreau moved in to a small cabin in Concord, MA in the woods next to Walden Pond. He lived deliberately, and took very detailed notes about the animals and plants that shared his woods.
After his death, his woods were well protected. Concord is prosperous and liberal even by Massachusetts standards, and takes its historical and natural heritage quite seriously. Over 60% of the areas that were wild during Thoreau's time are still protected.
Nevertheless, most of the flowering plants Thoreau observed are locally extinct or soon will be.
Even worse, there is strong evidence that the local extinction is just one small piece of the ongoing global extinction caused by Global Warming, and provides still more evidence that Global Warming may kill most of the world's species of plants and animals.
From 2003 to 2007, a graduate student from Boston University performed a careful analysis of all the flowering plants that could be found in the Walden Woods. They then compared this to a similar catalog of 473 species noted by Thoreau between 1852 and 1858, and another catalog made by the naturlist Alfred Hosmer in 1878, and 1888-1902. The results of this comparison (and subsequent analysis performed by computational biologists at Harvard) were published (pdf)in the Proceedings of the National Academy of Sciences.
Walden Pond and woods in autumn
The major result the recent survey found was that
27% of the species documented by Thoreau have been lost, and 36% exist in such low population abundances that their extirpation may be imminent
However, certain types of plants were hit hardest, particularly asters, bladderworts, buttercups, dogwoods, lilies, louseworts, mints, orchids, saxifrages, and violets.
Asters
The scientists naturally wondered what these had in common, and why they went (locally) extinct. The answer turned out to be fairly straightforward.
Species that survived tended to 1) flower earlier in the year than they used to, 2) be more flexible about what time of year they could flower as temperature conditions changed, 3) have more of their range located south of Concord, and less to the north. Species that vanished, or are vanishing, tend not to have these characteristics.
And these results, in turn, have a simple explanation. The average temperature in Concord has increased by 2.4C (about 3.8F) over the last century. Some plants have managed to adopt by changing their flowering times, or else were already accustomed to slightly warmer temperatures of more southerly climates.
Plants that were not able to adapt to these modest temperature changes disappeared.
Lillies
This study (like all good studies) leaves some open questions. Why would a change of only a few degrees cause such dramatic effects? The authors of the study don't know, but they note that insects' life cycles are cued to temperature, and that insects have therefore adapated to warming already. Flowers have to adopt to insects (to ensure they are fertilized and to avoid getting eaten). Flowers that adopted to temperatures in sync with insects have survived, while others have not.
Implications
This example illustrates a few clear lessons of climate change:
A temperature change of a few degrees can have large effects.
In order for a species to survive climate change, all the species on which it depends must do so as well.
Protecting land and/or leaving it undeveloped will not ensure its species will survive.
Finally, there is no reason to believe that Concord's experience is unusual. Other studies have shown that birds are moving north in other parts of the world as the climate warms. If they can not find food in their more northerly range, they will die.
All around the world, some species will move north in response to climate change. Others will adjust their life cycles (as did the surviving plants in the Concord's study). Still others will do nothing (because their life cycle events are cued by hours of daylight or something similar). Any species that find themselves out of sync with predators or prey will die.
Climate scientists know this. As the great climate scientist James Hansen wrote:
If we continue on [our current carbon emissions] path, a large fraction of the species on Earth, as many as 50 percent or more, may become extinct.
But it now seems that Hansen was too optimistic. The extinction of 50% of species is not something that "may" happen. Even in the pristine woods of Thoreau's Walden Pond in a wealthy, liberal community, it now appears inevitable.
Violets