Changes in the flora of Thoreau's Concord

摘要

To determine the effectiveness of conservation efforts, scientists and land managers must evaluate the ability of conservation areas to protect biological diversity. The historic town of Concord, Massachusetts, home of the philosopher and naturalist Henry David Thoreau, provides a unique opportunity to examine how well conservation areas preserve biodiversity in a suburban landscape. About 35% of total land area in the town has been protected, and botanists, including Thoreau, have surveyed plants in Concord five times over the last 170 years. We spent 5 years (2003-2007) re-surveying a subset of Concord's flora for species presence and abundance. Of the species seen by Thoreau in the mid-19th century in Concord, we could not locate 27%, and an additional 36% persist in one or two populations where they are vulnerable to local extinction. Most species losses appear to have occurred in the past three to four decades. Certain groups, such as orchids, have shown particularly severe losses. More native species are declining in abundance than are increasing. Non-native species represent an increasing percentage of the flora, with many increasing in abundance. The flora has experienced a net loss of species over the past four decades, with 82 species gained and 236 species missing. Because many species are rare on a local scale, persisting as one or two small populations, local extinctions will likely continue in coming decades. Habitat management, primarily to prevent tree establishment, appears to have allowed many rare species of open habitats to persist and recover. Active management of existing sites will likely be the key to protecting the species diversity of the Concord flora and maintaining the living connection to the writings of Thoreau.