Wildflower declines in Thoreau's Concord woods are due to climate changes

Rapid changes in temperature which have led to changes in the timing of seasonal activities, such as flowering, make some closely related groups of species – notably orchids, dogwoods, lilies and many sunflower relatives — more susceptible to swift declines than others.

These cautionary findings were developed based on a continuing study of 473 species in the fields, wetlands and deciduous forest of Concord, Massachusetts where changes in flowering times were first inventoried by Henry David Thoreau 156 years ago and regularly updated since then.

A phylogenetic or evolutionary context now provides an important predictive value for thinking about which plant species will be lost due to rapid climate change, noted Boston University conservation biologist Richard Primack. He is an author of the research study titled “Phylogenetic patterns of species loss in Thoreau's woods are driven by climate change,” that appears in the Proceedings of the National Academy of Sciences online today.

Since 2002, he and his students have actively tracked how warming temperatures have shifted the flowering times of plant species in the woods at Walden Pond and elsewhere in Concord. . They now find that wildflower species are also declining and being lost due to climate change.

The other authors are Charles G. Willis, Brad Ruhfel and Charles C. Davis of the Department of Organismic and Evolutionary Biology at the Harvard University Herbaria along with Abraham J. Miller-Rushing, formerly of Boston University's Department of Biology.

They concluded that the climate-influenced loss of plant diversity has been so great in Concord, despite 60% of the area being well protected or underdeveloped since Thoreau's time, that a global approach to conservation prioritization is necessary to minimize future species loss. And conservation strategies will require information both on the current ecology of the species as well as their past evolutionary history.

Their study, which examines changes in species abundance and habitat along with two separate measures of flowering time response to temperature, notes that since Thoreau's time species flower an average of seven days earlier. Moreover, the mean temperature in the Concord area has risen 2.4 degrees Celsius over the past 100 years and is expected to climb between 1.1 and 6.4 degrees Celsius during the next 100 years. These temperature changes are linked to flowering times.

“Species whose flowering time are not responsive to changes in temperature are decreasing in abundance,” the study states. “Most strikingly, species with the ability to track short-term seasonable temperature variation have faired significantly better under recent warming trends. In addition, species whose flowering times have shifted to be earlier in the years over the long-term have also fared significantly better under recent warming trends. Based on our regression estimates, change in abundance over the last 100 years is greatest when assessed against species' ability to track short-term seasonal temperature versus long-term flowering shifts. Thus, the association between flowering time tracking and change in abundance is a better estimator of species response to rising temperatures.”

The study also accounted for other plant life cycle influences such as the lack of available insect pollinators or the increased flower or seed predation. The authors found the phonological response to insects may correlate with seasonable temperatures. This suggests that plant species that respond to temperature changes may be better at maintaining important periodic interactions with pollinators or better at avoiding negative interactions such as predation.

The population declines of specific flowering species – those that did not respond to temperature – included anemones and buttercups, asters and campanulas, bluets, bladderworts, dogwoods, lilies, mints, orchids, roses, saxifrages and violets.