Dendroecology and climatic impacts for a relict, old-growth, bog forest inthe Ridge and Valley Province of central Pennsylvania, USA

We report on the 440-year dendrochronological history of a relict, bog fore st in the Ridge and Valley Province of central Pennsylvania that contains e xtreme southern, disjunct populations of Picea mariana (Mill.) BSP and Abie s balsamea (L.) Mill. The forest is dominated by Tsuga canadensis (L.) Carr . (49% relative importance value), Picea mariana (16%), and Acer rubrum L. (15%). The few remaining Abies balsamea trees are in a advanced state of de cline. Many Nyssa sylvatica Marsh. and T. canadensis trees recruited from 1 560 and 1700, respectively, until 1890. However, the majority of the other tree species recruited during a 40-year period following selective logging of the forest in the 1890s and fires in about 1900 and 1914. We found a sca rcity of tree saplings and no evidence of recruitment into the tree-size cl ass for any species after 1950. The master tree-ring chronology for both N. sylvatica and T. canadensis exhibits a marked increase after the 1890s log ging and a decrease after a 1900 fire. In addition, a large number of relea ses in individual tree chronologies occurred over the last 400 years, indic ating the frequent occurrence of small-scale disturbances. Tree-ring growth during the 20th century was reduced by droughts and cool temperatures in t he 1920s and in the early to middle 1960s. Abies balsamea cores exhibit a m arked growth decline in 1986. Tsuga canadensis growth was very low between 1970 and 1998, despite a generally warm and wet climate during that time. P icea mariana had a dramatic increase in growth during very warm and wet cli mate between 1995 and 1998. Most Abies balsamea trees have reached their pa thological age of 50-85 years and have active Armillaria root rot, insect i nfestations, and very poorly developed crowns. These symptoms or severe gro wth declines are not present in Picea mariana. It appears that the 10 000 y ear history of Abies balsamea presence at Bear Meadows will end soon, with no opportunity to reestablish itself because of the lack of a local seed so urce. The results of this study suggest that relict tree populations in the eastern United States may be particularly sensitive to direct and indirect anthropogenic impacts and climatic variations, and represent important ben chmarks for comparisons with future studies.