The size of the snowdrift trapped by the belt is also affected by the density. Green ash is a less dense species and, therefore, snow distribution behind a green ash shelterbelt will be more evenly spread across the field. Shrubs, such as caragana, chokecherry and Villosa lilac, provide superior snow trapping and wind protection due to their density but are not as tall as the ash or pine. These species can be used in areas where snow is not a concern, or where maximum protection is required. Figure 2 To get the appropriate density use species possessing the desired characteristics.
Many people choose to mix ash into a shrub row to provide extra height.
This results in a shelterbelt with the density of a shrub row, but the height of a tree row. A series of shelterbelts is a more effective shelterbelt system then a single row planted to protect a large area. The first row to meet prevailing winds should be less dense allowing for a more even snow distribution across the field. As this first row may intercept snow blowing from a considerable distance you should be aware of the amount of snow this shelterbelt could potentially trap. The other rows in the shelterbelt system can consist of denser species as there will be significantly less snow for these trees to trap.