102 JOURNAL OF FORESTRY 



Miami soil is Oucrcus macrocarpa. It attains a diameter of 3 to 5 feet 

 and a height estimated at 50 to 60 feet. One bur oak in our Jasper 

 County area yielded 137 fence posts. With it occur Querciis alba, 

 Quercus velutina, Quercus rubra, Carya ovata, Prunus serotina, Pop- 

 ultis tremuloides, and Ulmus americana. Tilia americana and Celtis 

 occidentalis are found at lower levels. Acer saccharinum is local. 



The foliage of these trees never attains great density. Thick under- 

 growth of hazel and other shrubs is common, and in many places at 

 present good pasturage of blue-grass (Poa pratensis) is found through- 

 out the groves. The trees also stand sparsely on the ground. On one 

 area near Searsboro (Mahaska County) 62 trees were found on an 

 area 50 by 100 feet, making about 496 trees per acre. Of these 62 trees, 

 only 29 were of a diameter of 6 inches or above. This was an espe- 

 cially dense patch of fenced timber, untrodden by stock. The ground 

 was covered with leaves and leaf mold ; there was no grass and com- 

 paratively little underbrush (see Table i ) . A plot in Poweshiek County 

 showed 211 trees per acre (see Table 2), of which 156 were 6 inches 

 or more in diameter. 



The outstanding characters of all the timber in this vicinity are the 

 low stature of the trees, the rather thin covering of foliage, admitting 

 much light, and the thinness or absence of leaf mold on the ground. 

 It is further noticeable that the timber is much more plentiful on the 

 slopes which face north or northeast than on any other slope. These 

 slopes are usually steeper than those on the opposite sides of the valley 

 and therefore less clearing has been done upon them. The timber may 

 also have prevented general erosion and tended to produce this peculiar 

 topography. 



Several observers agree that since this region was settled the oak and 

 hickory timber has spread up and out upon the prairie. Looking across 

 the hills southwest of Searsboro, we are told that 50 years ago one 

 could see over the hilltops for miles, where now the view is entirely 

 shut in by natural timber. Marked encroachment has occurred also 

 southwest of Grinnell. This advance cannot be accounted for by a 

 change of climate. It must be due either to the weakening of the prairie 

 grass due to tillage and pasturage or to the elimination of the prairie 

 fires. Under the circumstances, the latter theory seems decidedly pref- 

 erable. 



The rate of growth of timber on the Miami silt loam is good, but 

 very few of the trees attain to any great age. Three or four foot oaks 

 must have been some hundreds of years in growing ; but we rarely find 

 such. Few counts run over 100 years, and this of course dates far back 



