Long-term Growth Trends Research Articles

A Model-Based Approach to Tree Ring Analysis

SUMMARY The traditional steps in a tree ring analysis are reviewed and evaluated using a model-based approach. A growth model formulation is developed that allows all of the traditional steps to be handled simultaneously. The new method is applied to slash pine (Pinus elliotii Engelm.) tree cores from a nearly even-aged stand in Mississippi. The Kalman filter provides the analytical machinery for these applications. Tree rings offer a look into the past of a temperate forest that may be unavailable from any other source. The fact that tree rings can be crossdated [in the sense of Fritts (1976)] is key to their analytical value, and one of the most successful early uses of tree rings was for dating Peublo Indian structures in the Southwestern United States (Trefil, 1985). Currently, tree rings are being used in the study of air pollution effects on forests, and crossdating plays an important role in ensuring that replicate time series are obtained by coring a number of trees. Following data collection and crossdating, analyses of climate relationships and long-term patterns of growth are of interest. Dendrochronologists have recommended procedures for analyzing tree ring data that are critically reviewed here. The motivation behind these procedures is sound, but the possibility for user subjectivity to bias the end results exists, and the need to process each core individually can become overwhelming on large data sets. Therefore, following a critical review of usual procedures, a model-based method for analyzing long-term growth trends and climate relationships is developed. The model-based approach handles the entire analysis simultaneously and can be evaluated more easily in terms of model validity and statistical tests than the traditional approach.

Decline in long-term growth trends of white oak

White oak (Quercusalba L.) tree-ring collections from 89 locations throughout much of its range, from Connecticut to North Carolina to Iowa, were examined for evidence of growth decline initiated in the 1950's. The expected trend of annual basal area increments, based on pre-1950 growth, appears to be linear, with the slope varying among collections relative to site quality. Growth decline, defined as departure of actual growth below that expected, was identified in 40 of 60 collections judged to have not been affected by local site histories. The percentage of collections showing decline was essentially the same in the Northeast, the Midwest, and the Southeast. Onset of decline began during a relatively narrow time window from the mid-1950's to the early 1960's. Since then the growth trend has been linear and appears unrelated to changes in regional sulfur and nitrogen oxide emissions. It is postulated that events or conditions, unique to the 1950's, initiated a growth rate change in about two thirds of the white oak stands examined. Initiation of the decline appears to be unrelated to tree age, geographic location, site quality, climatic trends, or regional emissions of sulfur and nitrogen oxides.

Long-Term Cyclical Trends in Growth of Lake Whitefish in South Bay, Lake Huron

A 39-year series of samples (1947–1985) was obtained with gill nets and trawls from a discrete population of lake whitefish Coregonus clupeaformis within the innermost basin of South Bay, Manitoulin Island, in northern Lake Huron. Back-calculations based on scales allowed growth in weight to be estimated for 47 year classes of lake whitefish. Growth of young fish prior to entry into exploited sizes was slow in the mid-1930s, increased to a maximum in the early 1950s, declined again to a minimum in the late 1960s, and increased again during the 1970s and early 1980s. Trend analyses with Fourier transformations provided cyclic sine wave models with a 32-year period that fit growth trends better (higher r2) than either linear or polynomial models. Long-term cycles in water level and temperature correlate significantly with the observed growth cycle. These two environmental factors account for 88% of the variation in lake whitefish growth, leaving 12% to be accounted for by community interactions. Based on observations in South Bay and fishery studies in other areas of the province, a hypothesis is suggested that long-term fluctuations in the hydrological cycle and other climatic factors interact to control long-term fluctuations in fish production throughout Ontario.