40 The Botanical Survey of Nebraska 



average daily rate of evaporation is an important factor where 

 high water losses are concerned. 



FURTHER STUDIES IN THE FOREST COMMUNITIES 



It has already been pointed out that the dififerent forest dom- 

 inants, although frequently occurring in apparent mictia, usually 

 are grouped in more or less distinct communities. Even casual 

 observation shows the dominance of Tilia americana and Quercus 

 rubra in the ravines at the bases of the moist slopes ; of Quercus 

 macrocarpa on the drier crests, with Quercus velutina, Hicoria 

 ovata, and other trees occupying intermediate positions. 



Belt transects lo meters wide were run from the crest to the 

 foot of several slopes. At intervals of 8 meters cross tapes were 

 inserted and in the areas thus delimited a census was taken of the 

 tree population together with their diameter B. H. Each tree was 

 charted in its relative position in the area. One of these transects 

 showing the height and slope of the hill, the charted areas and the 

 plant communities they pass through is shown in figure 15. 



This figure is very illuminating and worth careful considera- 

 tion. The transect at the foot of the chart -shows the exact num- 

 ber, diameter and position of every woody plant (exclusive of 

 seedlings) growing on the area. The transect at the top of the 

 chart is merely a summary statement of the corresponding areas 

 shown below. In every case the dominants have been placed 

 first. They are preceded by numbers which, indicate their abun- 

 dance in the area and are followed by an exponent which gives the 

 average diameter in inches. In a similar manner the other trees in 

 the particular area are summarized. For example, an examina- 

 tion of the area (10 X 8 meters) on the extreme right at the foot 

 of the figure shows that Tilia is dominant, that seven trees of this 

 species occur in the area and that they have an average diameter 

 of 7 inches. Also one Quercus rubra with a diameter of 4 inches 

 occurs here. This is summarized in the corresponding area at 

 the upper right corner of the figure. 



From these summaries it is relatively easy to delimit in a quan- 

 titative manner and with a considerable degree of accuracy the 



46 



