FORESTRY QUARTERLY 



Vol. XII December, 1914 No. 4 



A MECHANICAL MODEL OF A REGULATED FOREST. 

 By O. L. Sponsler and E. C. Luebben. 



A mechanical model designed to demonstrate the growth of a 

 "clean-cut and planted" forest, under regulation, was built and 

 used as a part of the annual exhibit given jointly by the students 

 of the Engineering Department and of the Forestry Department 

 of the University of Michigan. The incentive for making this 

 model was a desire to impress, at a glance, the idea that a forest 

 can have a crop of timber to harA^est at regular intervals and 

 that all of the different sizes are gradually becoming larger. We 

 wanted to show a series of 10 areas, each with a different age 

 class ranging from 1 to 10; and we wanted the stand on each 

 area to slowly grow taller, while the people were looking on, 

 until the end of its rotation, when it would disappear and a new 

 crop start on the denuded area. We did not intend to show an 

 ideal area arrangement of the age classes of a forest, and the 

 model does not do that; but rather we wanted to visualize a 

 growing forest and convey the idea of crops harvested at regu- 

 lar intervals. At least 10,000 people saw the exhibit and the 

 majority of those who were interested in this model, which in- 

 cidentally formed quite a center of attraction, readily saw the 

 points we wanted it to demonstrate. We mention this to show 

 that the model is worth while and worth more thought. 



Our first model, the one described and illustrated, is a very 

 crude affair in construction and had to be built in a hurry, 

 so simplicity was a necessity. The single cam idea on a main 

 shaft for raising each compartment, was adopted as the simplest 

 and most easily made, after quite thoroughly considering various 

 arrangements of two cams for each compartment, individual and 

 main shafts, racks and pinions, and sprockets and chains com- 

 bined in many different ways. 



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