WINDBREAKS: THEIR INFLUENCE AND VALUE 



A REVIEW OF FOREST SERVICE BULLETIN 86. BY CARLOS G. BATES 



BY GEORGE L. CLOTHIER 



IS publication fills a long felt want and is the most exhaustive treat- 

 merit of the subject of windbreaks ever attempted in this country. 

 The magnitude of the investigations made by the Forest Service as 

 a basis for this bulletin may be appreciated when it is known that the extent 

 of branching of the various species was determined from measurements of 

 1319 plantations. The effect of plantations on evaporation was learned from 

 865 hourly readings of evaporometers. The observations were distributed 

 through the months of June, July. August, and September, 1908. 



The horizontal extent of tree roots into cultivated land adjacent to the 

 windbreaks was determined for 152 groves representing eight species. Effects 

 on temperature were derived from 30 readings, and crop yields were studied 

 in 12 fields. 



The bulletin is divided into four parts. Part I is a synopsis of the 

 conditions which the study attempted to measure. Part II is a record of 

 the measurements of the physical factors entering into the problem with 

 interpretations of the physiological effects of these factors upon animal 

 and plant lift. Part III deals with the timber production of windbreaks 

 and shows how to assess their cost against the land they have damaged and 

 occupied. Part IV summarizes the protective value of windbreaks and 

 calculates the profitable area to devote to windbreaks of various species. 

 Specific recommendations for planting in the several regions needing wind- 

 breaks are found in the concluding pages of the bulletin. 



The study was carried on chiefly in the States of Kansas and Nebraska, 

 although some measurements were made in Iowa and Minnesota. The sea- 

 son chosen for the study proved to be more humid than the average with less 

 wind in the summer months than usually occurs in the region, hence the 

 effects abserved may be taken as underestimates rather than over estimates 

 of the influence of windbreaks. 



The study showed that a windbreak may be both beneficial and harmful 

 to the crops of an adjacent field. The observations showed that for the 

 summer months a windbreak may reduce the mechanical force of the wind, 

 lessen evaporation, stagnate the air or reduce its velocity, increase extremes 

 of temperature both in the air and the soil, and change the distribution of 

 moisture in the soil. In studying both beneficial and harmful influences, 

 measurements and observations made in and near the windbreaks were com- 

 pared with measurements made far enough away to be outside of the in- 

 fluences. The distances through which the effects of the plantations were 

 manifested were measured in all cases in terms of height of the trees, since 

 both beneficial and harmful effects are directly proportional to the height of 

 the trees. 



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