In his meticulous notes on the natural history of Concord, Massachusetts, Henry David Thoreau records the first open flowers of highbush blueberry on May 11, 1853. If he were to look for the first blueberry flowers in Concord today, mid-May would be too late. In the 160 years since Thoreau’s writings, warming temperatures have pushed blueberry flowering three weeks earlier than in Thoreau’s time. The climate around Thoreau’s beloved Walden Pond is changing, with visible ecological consequences. In his new book, Walden Warming, Richard B. Primack, PhD, Professor of Biology, Boston University,  uses Thoreau and Walden, icons of the conservation movement, to track the effects of a warming climate on Concord’s plants and animals. Under the attentive eyes of Primack, the notes that Thoreau made years ago are transformed from charming observations into scientific data sets. Primack finds that many wildflower species that Thoreau observed have declined in abundance or have disappeared from Concord. Hear how warming temperatures have altered these and other aspects of Thoreau’s Concord, from the dates when ice departs from Walden Pond in late winter, to the arrival of birds in the spring, to the populations of fish, salamanders, and butterflies that live in the woodlands, river meadows, and ponds. The Arnold Arboretum program will take place Wednesday, April 30, from 7 – 8:30 in the Hunnewell Building of the Arboretum.  Free for Arboretum members, $5 for nonmembers.  Register online at www.my.arboretum.harvard.edu.