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Introduction

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Virtual Windbreak

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Density

Windbreak density is based on the a view of the long side of a windbreak.  It is the ratio of the solid portion of the windbreak to the total area of the windbreak.  Density is a very important component of windbreak structure because it affects the length of the protected zone, both upwind and downwind from the windbreak.  Windbreak density is usually divided into rather broad ranges:

 

  • <20% - Young, establishing windbreaks or old, mostly-dead single-row windbreaks. Minimal protection provided.

  • 20-40% - Established single row windbreaks consisting of deciduous trees (Fig. 2-1).

  • 40-60% - Established single row windbreaks consisting of conifers.

  • 60-80% - Multiple-row windbreaks, usually consisting of a mixture of conifers and deciduous trees (Fig. 2-2A and B).

  • >80% - Multiple-row windbreaks often including more than one row of densely-branched conifers such as spruces (Fig. 2-3).

 

Figure 2-1. Single-row deciduous windbreak, 20-40% density.  This density is effective in crop protection, but the higher density at the bottom of the windbreak will not allow much snow spreading across the field.  Photo by Joe Zeleznik.

Single-row deciduous windbreak, 20-40% density. This density is effective in crop protection, but the higher density at the bottom of the windbreak will not allow much snow spreading across the field

 

 

Figure 2-2. Multiple-row, mixed deciduous and conifer windbreaks, in summer and winter. A. Summer density is 50-70% at the top, >80% at the bottom of the windbreak.  B.  Winter density in a similar windbreak is 40-60% at the top, 60-80% near the bottom.  These windbreaks are vital in controlling snow placement and are both used as "living snow fences" along roads and highways.  Photos by Joe Zeleznik.

Multiple-row, mixed deciduous and conifer windbreak in summer.Summer density is 50-70% at the top, >80% at the bottom of the windbreak. These windbreaks are vital in controlling snow placement and are used as "living snow fences" along roads and highways.

Multiple-row, mixed deciduous and conifer windbreak in winter. Winter density is 40-60% at the top, 60-80% near the bottom. These windbreaks are vital in controlling snow placement and are used as "living snow fences" along roads and highways.

 

 

Figure 2-3.  Very-high-density mixed deciduous and conifer windbreak, >80% density.  Wind protection in winter is outstanding, but remains for only a short distance downwind of the windbreak. Summer temperatures behind this windbreak may be stifling, as winds will barely penetrate the tree canopy.  Photo by Joe Zeleznik.

Very-high-density mixed deciduous and conifer windbreak, >80% density. Wind protection in winter is outstanding, but remains for only a short distance downwind of the windbreak. Summer temperatures behind this windbreak may be stifling, as winds will barely penetrate the tree canopy.

 
 

How does a windbreak work?

Density

Length of protected zone

What is the correct density?

Natural changes in density

Insects and diseases