212 ILLINOIS STATE ACADEMY OF SCIENCE 



more tolerant species, while not competing with the over- 

 wood of cottonwood and sycamore, will persist at a 

 slower growth rate, or will seed in under the tolerant 

 trees. With the removal of the latter the site will be oc- 

 cupied and held by the elm, maple, oak, hackberry, honey 

 locust and ash. 



Within this grouping of the more tolerant species there 

 will be a sharp struggle for crown space, and the check 

 in crown expansion will be reflected in a correspondingly 

 poor diameter growth. 



Thus, under the conditions which exist in these all-aged 

 stands, the two species which show unusually rapid 

 growth are the species which must have an abundance of 

 sunlight; therefore they occur locally in the bottomland 

 as an early stage in the transition from the new land to 

 the ultimate forest, and where occurring, make a uni- 

 formly high rate of growth. 



In attempting to grow either sycamore or cottonwood 

 in pure even-aged stands the average diameter growth 

 would probably be less than that of these same species 

 growing in a mixed stand, for the reason that in the 

 mixed forest the sycamore or cottonwood carry their 

 crowns well up above the other species with consequently 

 more leaf exposure to sunlight. The average diameter 

 growth of the more tolerant species grown in pure even- 

 aged stands probably would be increased, because at no 

 period of their growth would there be an overwood with 

 consequent suppression. In the management of such 

 even-aged stands the suppression resulting from lateral 

 crowding would be modified by thinnings in the plan- 

 tation. 



In the natural grouping of this all-aged virgin bottom- 

 land stand the average yield per acre is 15,000 B. F. The 

 average age of the merchantable trees is slightly over 

 100 years. Cottonwood and sycamore made a diameter 

 growth inside the bark on the stump of 20 inches in 40 

 years, pin oak in 58, honey locust in 57, soft maple in 59, 

 hackberry in 125, elm in 127, and ash in 150 years. 



In conclusion, it seems evident that the highest re- 

 turns can be secured from a naturally stocked bottomland 

 area by encouraging the sycamore, cottonwood, pin oak 



