Censusing and modeling the dynamics of a population of Eastern Hemlock (Tsuga canadensis) using remote sensing.

W. Robert Lamar, Biology Department, West Virginia University, rlamar@swva.net

James McGraw, Biology Department, West Virginia University, jmcgraw@wvu.edu

A population of Eastern Hemlock (Tsuga canadensis) was censused over a three-year period (1997-1999) from the ground using traditional field methods and from the air using large scale, high-resolution aerial imagery. 529 of the 1401 individuals measured on the ground were also visible in the aerial census. Tree size, crown density and crown position all played roles in determining a crown’s visibility from the air. Almost all large, upper canopy hemlocks were detected in the aerial census. Small, suppressed hemlocks occupying the more open forest locations comprised nearly 40% of the aerial population.

Automated spectral and spatial segmentation procedures were developed to identify and measure individual crown modules within the population. A crown module was defined as a distinct portion of crown canopy segmented from its neighbors on the basis of size, shape, and distance. Within the multi-temporal imagery, 65.7 - 70.7% of the identified crown modules were closely associated with a single hemlock individual censused on the ground. The other crown modules represented isolated portions of a single hemlock crown or multiple crowns growing in a clumped cluster. An automated crown reconciliation procedure was developed to ensure the compatibility of multiple year data sets. The population of crown modules was divided into a size classes and the fate of individual modules followed over time. Transitions between size classes, the appearance (birth) of new modules and disappearance (death) of modules were incorporated into a matrix population model. Population characteristics; overall population growth rate, reproductive values, elasticity values, and stable stage distributions are derived from the model.