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Abstract
This study addressed three general problems: (1) present an ecological description of Maine's forests, (2) characterize population parameters under various biotic, abiotic, and disturbance conditions, and (3) investigate relationships between disturbance and species composition.
Data were from 769 permanent plots measured in 1957, 1969, and 1981 as part of ongoing statewide forest inventories. While data provided new characterizations of forest land by climate, soil, slope, elevation, and productivity, ordination techniques revealed that some environmental variables important for explaining forest community structure were not gathered. Analyses identified problems with productivity classifications and which site variables provided redundant information. Species abundances best fit a geometric series distribution, supporting the niche pre-emption hypothesis of division of community resources.
A four-stage matrix population model estimated population growth and survival/mortality rates for balsam fir, red spruce, and red maple. Elevation, soil site quality, and rooting depth had no consistent influence on population parameters. Higher stocking levels led to lower population growth and survival rates, and shade tolerance was not a dominant factor determining species response. Harvest had a greater impact than natural disturbance. Balsam fir was affected most by disturbance. The assumption of time-homogeneous transition probabilities in stationary Markov chains is invalid in many situations, and projections can vary widely without proper accounting of disturbance. Results showed a decline of spruce-fir populations between 1957 and 1981, which may be explained by multiple factors (e.g., species longevity, disturbance, and air pollution).
A new technique of coupling detrended correspondence analysis and Euclidean distance dissimilarity measure was used to evaluate relationships between disturbance and species composition of red spruce-balsam fir stands. Much of the variation of successional paths across the 23-year period was due to various types and severities of disturbance, but many other factors were important. There were no significant differences between shorter intervals with respect to compositional change. Results indicated that cutting changed composition more than natural disturbance. Increased spruce budworm activity resulted in an increased rate of succession, with balsam fir declining relative to red spruce. More specific data on disturbance would enhance the value of forest inventories in studying forest succession.
