Showing papers on "Undergrowth published in 1991"

Population dynamics and demography of the bank vole in different tree stands

Abstract: The seasonal and multi-annual changes in numbers and demography of the population of Clelhrionomys glareolus (Schreber, 1780) in nine different stands which differed in spatial structure and plant species were analyzed. The density and distribution of the undergrowth influenced the density and demography of the population. On plots where the undergrowth was more evenly distributed (random) there was a higher density than on plots where it was clustered. The multi-annual cycle showed a synchronizatio n of density changes (across all plots). The number of sexually active males and females decreased as the clumping of undergrowth increased. The number of recruits to the population was proportionate to the number of sexually active females at the beginning and end of the reproductive season. In late summer there was a decrease in recruitment to the population, especially on plots with randomly distributed undergrowth. The number of recruits to the population in a given trapping series was inversely related to the number of individuals persisting from the previous trapping series. The higher survival rates of individuals marked in the early summer on plots with random dispersion of undergrowth caused the age structure of the individuals on these plots to "become older" than on plots with clustered undergrowth. These results are in agreement with Anderson's model for utilization of habitats along a decreasing gradient of suitability for the bank vole and indicate that processes regulating the population most effectively occur early in the season.

Forest growth conditions analysis using multiple source digital image data

Abstract: Relationships between multiple source raster format data and forest growth factor combinations were analyzed. The growth factors were assumed to become apparent as dominant tree species and type of undergrowth vegetation. The study area, centered at 63" 28' N, 26" 14' E, was located in Middle Finnish boreal forest. The field data were 2 1 1 1 sample plots of the National Forest Survey. Image data consisted of Landsat MSS images, topographical, soil, geochemical and geophysical variables. The main analysis methods were t-test, correlation, discriminant and clustering analyses. The best image variables to estimate growth factors were MSS channels, gamma radiation and geochemical variables.