Porosity and Drag Determination of a Single-Row Vegetative Barrier (Maclura pomifera)

Deciduous trees of the species (Osage orange) are commonly established as vegetative barriers for wind erosion control throughout the U.S. Great Plains. Because there is no previous research on the aerodynamic effectiveness of these vegetative barriers during different seasons (leaf-on and leaf-off conditions), this study focused on determining the porosity and drag characteristics of this tree species. Digital image analyses were used to determine optical porosities that were then correlated with barrier drag coefficients. Images were taken in the field during calm wind conditions when the sunlight was suitable for digital imaging. Wind speeds were measured at different heights for a single-row Osage orange barrier using cup anemometers. Two anemometer towers were positioned relative to the barrier. One was located windward at 10H distance from the barrier; the other was located leeward and was movable to distances of 1H, 2H, 4H, 7H, 10H, 12H, 15H, and 20H from the barrier, where H is the average barrier height. The wind speeds measured in the field ranged from 4 to 7 m s-1, with lower wind speeds encountered during the leaf-off condition. As expected, wind speed reductions were greater for the leaf-on condition and ranged from 40% to 80% at 1H from the barrier, while the reduction was 20% to 38% for the leaf-off condition. The crown portion of the barrier was found to be responsible for much of the reduction. Mean values of the drag coefficient were 1.3 for the leaf-on condition, decreasing to 0.9 for the leaf-off condition of the Osage orange barrier, which corresponded to mean optical porosities of 20% and 61%, respectively Keywords: Drag coefficient, Image analysis, Osage orange, Porosity, Vegetative barrier, Wind erosion.

Modelling of the Influence of Vegetative Barrier on Concentration of PM10 and PM2,5 from Highway

The influence of different types of the vegetative barrier near a highway on dustiness was studied. Transport, dispersion and sedimentation of pollutants PM10 and PM2.5 emitted from the highway was numerically simulated. Mathematical model was based on the Navier-Stokes equations for turbulent fluid flow in Boussinesq approximation. The AUSM-MUSCL scheme in finite volume formulation on structured orthogonal grid was used.The influence of the shape of the barrier and of its obstructing properties on the concentration of pollutants was studied.

Woody Shrubs as a Barrier to Invasion by Cogongrass (Imperata cylindrica)

Cogongrass invades forests through rhizomatous growth and wind-dispersed seeds. Increased density and abundance of woody vegetation along forest edges may strengthen biotic resistance to invasion by creating a vegetative barrier to dispersal, growth, or establishment of cogongrass. We evaluated differences in dispersal of cogongrass spikelets experimentally released from road edges into tallgrass-dominated and shrub-encroached longleaf pine forests (Pinus palustris). Average maximum dispersal distances were greater in the pine–tallgrass forest (17.3 m) compared to the pine–shrub forest association (9.4 m). Spikelets were more likely to be intercepted by vegetation in pine–shrub forests compared to pine–tallgrass forests. Results suggest that dense woody vegetation along forest edges will slow spread from wind-dispersed cogongrass seeds.

Vegetative filter strips to control sediment movement in forest plantations: validation of a simple model using field data

A field study of sediment movement through vegetative barriers was carried out to assess the sediment-trapping effectiveness of vegetative barrier types typically used in forest forest plantation management in south-east Queensland, Australia, and to develop a simple methodology for predicting sediment movement through these barriers. For sites at the centre of Queensland's 110 000 ha Pinus plantation and 45 000 ha Araucaria plantation program, small field flumes (plots) were established on a range of vegetation types and slope gradients, and sediment-laden flows passed through them. Sediment trapping in the plots was assessed by comparing paired samples taken from the inlet and outlet of the plots at pre-determined sampling times. Measurements included total sediment and equivalent size distributions of sediment particles (the latter measurements being based on settling velocities). For plots that did not erode, the degree of sediment trapping, if based on total sediment only, was quite variable. However, if rates of transport were considered in terms of the various size fractions, results were very consistent. A simple conceptual approach equating the vegetated area to a sedimentation pond allowed deposition to be calculated on the basis of settling velocity, flow depth, and residence time within the vegetated area. Estimated transport rates of sediment through the vegetated areas were in close agreement with measured transport rates, confirming the eciency of this approach. The results highlight a number of issues for management of sediment movement from forest estates.