TREE GROWTH IN THE VICINITY OF GRINNELL, IOWA 



By Hi;nry S. Conard 

 Department of Botany, Grinnell College, Grinnell, Iowa 



We are filled with wonder when we stand today on what was once 

 the endless grassy prairie and find our view shut off on every side by 

 trees. Towns of thousands of inhabitants are almost hidden by foliage, 

 and of the school-houses that stand but two miles apart in each direc- 

 tion scarcely one-third would be detected in a bird's-eye view. Every 

 farm-house is sheltered, if not hidden, by trees, and there are groves 

 and orchards beside. Such, at least, is the landscape round about 

 Grinnell. We know not whether to wonder more at the evidence of 

 human industry or at the bountiful response of nature. Professor 

 Shimek^ has recently discussed in a masterly monograph the problem 

 of the prairie. Upon this ground, therefore, we now fear to tread. 

 The present paper presents some accurate data on tree growth in 

 Poweshiek, Jasper, and Mahaska counties, Iowa. These notes have 

 been collected by various observers during the past ten years; but the 

 fullest records are of certain tracts in Jasper County, collected by 

 Horace J. Adkins in the spring of 1912. 



Two types of soil cover probably 90 per cent of the region under 

 discussion — the Marshall and the Miami silt loams. Both are composed 

 primarily of the same fine-grained loess. The Marshall silt loam is 

 most typical on broad, level highlands, where the run-off of rainfall is 

 small. Soil moisture has favored the retention of humus from the 

 remains of countless generations of grasses; hence the dark color of 

 the soil. A large amount of calcium carbonate — triturated limestone 

 from the lowan glacial drift — keeps the soil sweet and friable. The 

 Miami silt loam is found on hilly ground, where better drainage favors 

 eremacausis. It is of a paler color and clayey texture, like the subsoil of 

 Marshall. In very small areas on hilly ground, where loess has either 

 failed to accumulate or has been washed away, appears the Marshall 

 loam. It is a pure, gravelly glacial drift, worked over by vegetation. 

 Along the streams is the black Kaskaskia loam. This forms a strip 

 proportional in width to the drainage basin in which it lies. On Skunk 



' Shimek, B. : The Prairies. Bulletin Lab. Nat. History, State Univ. Iowa, 

 Vol. 6, No. 2, pp. 171-240, 191 1. 



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