Effectiveness of shelterbelt with a non-uniform density distribution

The ecological project of shelterbelts in oasis–desert ecotone is a main measure to wind–sand damage, which is one of the most serious eco-environment problems in arid regions. The effectiveness of shelterbelts with a non-uniform density distribution, planted perpendicular to the prevailing wind direction, was studied through field observations. The results showed that the main factor influencing wind speed is the density distribution of a particular shelterbelt of a specifically given tree specie. In this study, the shelter effects of a sparse shelterbelt was compared with a dense shelterbelt and it corresponded with most previous reports, namely that dense shelterbelts resulted in a higher wind reduction whilst the sparse shelterbelts have a longer shelter distance at the leeward side of the belt. For shelterbelts with a non-uniform density distribution and wind blowing from high density to low density, wind speed changes will be similar to that of a high-density shelterbelt at both the windward and leeward sides of the shelterbelt. However, when the wind blows from the opposite direction, the flow fields change greatly as compared to an evenly distributed shelterbelt. A combined effect of density manifested, thus providing better shelter effects by balancing the reduction in wind speed with the shelter distance.