Abstract:

The dynamic balance method was used to deduce the relative power formula of the upper air flow to accurately assess the impact of a wide range of oasis protection forest on the upper air power speed. Based on the measurement at four different geometric structure grids, and the fitting estimates with the wind speed data collected from a 50 m flux tower at the Dengkou Desert Ecological Research Station, it was found the upper relative power speed during April and May gale periods within the oasis region was about 1.3. The following formula was built to estimate the ground layer relative wind speed (γ) and further to evaluate the effects of a wide range of oasis area on wind protection: γ=v_*'α√2l/[2α²l+(1-α²)A².This formula, based on the analysis of mechanisms of oasis protection forest edge zone and the upper power speed change, and constituent elements of power speed under shelterbelt trees, provided a ground resistance evaluation method of oasis area. This formula could also illustrate the relationship between wind penetration coefficient (α), forest space (l, which is the multiple of tree height), ratio of average wind speed and power speed below tree height in the control areas (A), and wind protection effect of the whole shelterbelts.

Key words: farmland shelterbelts, relative wind speed, permeability of windbreaks, distance between main belts, power speed