4 BULLETIN 933, U. S. DEPARTMENT OF AGRICULTURE. 



INFLUENCE OF SOIL AND CLIMATE UPON DISTRIBUTION. 



Throughout its wide range the local distribution of walnut is con- 

 trolled by climatic and soil factors, which affect not only its abun- 

 dance and commercial value but also the other species with which 

 it characteristically associates in the forest. In general, walnut is 

 found on rich, moist but well-drained soils. It is more dependent 

 upon these conditions than are many of its associates, and a rela- 

 tively slight inferiority in any of these respects may be reflected 

 either in a scarcity of walnut or in slow and scrubby growth. Its 

 dependence upon good soil is more marked, however, in regions in 

 the western part of its range, which have a relatively scant precipi- 

 tation, than it is in well-watered regions like those in the southern 

 Appalachians. In the latter situations it makes a better develop- 

 ment on rocky and shallow, though by no means sterile, soils than 

 could be expected elsewhere, compensation for the deficiency in soil 

 qualities being made by the abundance of the summer rains. 



West of the Wabash River and in the Mississippi Valley below 

 Illinois walnut of good development is almost invariably on rich 

 bottom lands. An exception to this is its occurrence in the Boston 

 Mountains of Arkansas, where because of the heavier precipitation 

 it is found on flat mountain tops and benches. It is, however, by no 

 means a stream-bank tree in the sense in which sycamore, river birch, 

 and willow are. These species, though frequently growing near by, 

 are rarely seen in intimate mixture with walnut except in the moister 

 places in the eastern part of its range. This is probably because the 

 soil for walnut must be not only moist but well drained and aerated 

 as well — a fact which, no doubt, also explains in large measure the 

 lack of walnut in such places as the Mississippi bottom lands, which 

 are subject to protracted flooding. The deficiency in soil aeration 

 may also be responsible for the exceedingly slow growth and virtual 

 failure of certain plantations on rich but exceedingly compact bot- 

 tom-land soils, heavily sodded and never thoroughly broken. 



LOCAL FORMS OF GROWTH AND ASSOCIATED SPECIES. 



Walnut is found in three characteristic situations — as scattered 

 field and fence-corner trees, as scattered trees in hardwood stands, 

 or as pure stands, usually on the edge of the hardwood forest. 



In fields, particularly in the Ohio River basin, it sometimes rep- 

 resents a remnant of the original stand, left because of its value when 

 the land was cleared for agriculture. The fence-corner trees have 

 come up because the uncultivated soil attracted squirrels to bury the 

 nuts there and because in such situations the trees were protected 

 from injury. Ever since the days of the great popularity of walnut 

 furniture there has been a tendency among farmers to conserve this 



