| Popis: |
Crystal Fen in north-central Maine has become well-known as a locality with numerous rare plants. Recent observations of apparent drying and an increase in abundance of woody vegetation in the fen have led to concerns that an adjacent railroad bed and drainage ditch may be causing changes that threaten the habitat of several rare and interesting plant taxa. A description of these changes comes from analysis of (1) aerial photographs dating from 1938 to the present; (2) characteristics of the present vegetation, including the age of living woody plants; (3) evidence of fire on the fen; and (4) the fossil-pollen and charcoal stratigraphy for the past 200 years from an area of the fen that is becoming increasingly wooded. Results indicate that during much of its history the fen may have been at least partially wooded, except in the area that is wettest and most open today. Construction of the railbed in 1893, and the passing of cinder-producing steam locomotives along the tracks thereafter, apparently promoted expansion of fen vegetation by impeding drainage and by igniting occasional fires that reduced the abundance of woody stems. Thus, the extensive open habitat where populations of some rare plants occur is, in fact, an artificial result of human activities. Recent drier conditions post-date the construction of a drainage ditch in 1937 and the introduction of diesel-powered locomotives around 1950, which largely eliminated the ignition of fires and allowed the re-expansion of woody taxa over most of the fen. This trend represents a partial retreat to natural conditions. The study demonstrates that (1) rare plants occur in a variety of habitats (open, lightly forested, and heavily forested) at Crystal Fen, suggesting that these populations would be best served by maintaining such habitat diversity; and (2) past human disturbance led to expansion of open areas, which is the habitat most suitable for some of the rare taxa. In the future, both open fen areas and overall habitat diversity could be artificially enhanced using a variety of management practices including cutting, prescribed burning, and manipulating drainage to maintain a mixture of vegetation types. |
