The above mentioned processes allow shrubs and trees themselves to take
more advantage of an increased water availability than nearby herbs or
crops. However, windbreaks in crop land areas are claimed to be able to
increase crop yields by increasing moisture availability due to lower
evapotranspiration and improved infiltration [14, 35]. Recent studies throw
doubts on this simplistic explanation [54]. Under dry conditions in the USA
protected crops may produce less, due to damage resulting from higher
temperatures [19]. Expectations for semi-arid West Africa mostly refer to the
case of the Majjia-valley in Niger, where deep, sandy soils, a high water table
and strong year-round winds, offer optimal conditions for the use of windbreaks.
However, no significant increase of crop-yields was measured [31].
On shallow soils windbreaks are difficult to establish and will cause a
decrease of overall crop-yields [26]. If windbreaks result in more water
becoming available for crops, it does not necessarily result in more production.
In such a case increased nutrient inputs may increase the effect of the
windbreak.