To study the influence of a forest canopy on thermodynamic processes taking place within the Atmospheric Boundary Layer (ABL) a prognostic one-dimensional ABL model including a forest canopy was developed further. It is the aim of this study to simulate for a horizontally homogeneous environment the energy fluxes as well as the vertical profiles of meteorological quantities and some turbulence parameters within and above a vertically high resoluted tall vegetation canopy with variable leaf area density. The set of non-linear model equations used in this study includes additional vegetation-specific terms. To avoid the complex formulations of higher-order closure but also a simple flux-gradient approach the model equations are closed by using one- and-a-half-order (K-b-l) closure principles that contain the advantage of small computational time requirements. Results of several numerical experiments substantiate the sensitivity of the model to different closure conditions (mixing length formulations) and values of the plant-specific parameters.