FOREST SURVEYS ON MICHIGAN STATE FORESTS 569 



Preliminary Instruction. — The men are given several days of prac- 

 tice and instruction in the work before starting the strip-cruising v^rork. 

 Several miles of line are run, and the methods of mapping topography, 

 need of accuracy in the work, methods of determining sites, types, etc., 

 thoroughly discussed. 



While two men are running the preliminary control lines the third 

 man is busied at making a silvical study of the forest. This includes 

 especially a study of the growth of the trees, of the age classes, of site 

 qualities, of identification of brush and herbs, of relations of insects 

 and fungi to the forest, and of those other matters concerning which 

 questions are asked on the questionary for the forest description. This 

 initial study, lasting only four or five days, but repeated whenever time 

 allows, is considered to be of real worth in assisting the men to a better 

 understanding of the forest in which they are working. The forest 

 descriptions and the site and planting maps certainly are done better 

 as a result of this study. 



Intensity of Work. — Two strips are run through each forty, thereby 

 making the usual lo per cent estimate. 



The forest descriptions, including the estimates, are applied to the 

 individual forties, which are here usually the permanent compartments. 

 If there is more than one type on a forty (usually there are at least 

 two types on each forty), then the descriptions and estimates are 

 written separately for each type (or lot). 



TOPOGRAPHIC MAP 



The lay of the land of the forests is mostly level ; what hills there 

 are here are not steep. In order to correctly portray this gently sloping 

 land a contour interval of lo feet is used. Mapping contours is not 

 easy, owing to the fact that an error of but a few feet in the elevation 

 determination of a point will often throw the location of the contour 

 at some considerable distance from its true location. Unless the eleva- 

 tions along adjoining strips are determined accurately the contours 

 drawn will not connect. To make them connect a good deal of fudg- 

 ing of lines must be done, with the result that a terrain is pictured that 

 is not found in replica in the field. In order to overcome this, the error 

 per mile of strip line in elevation is limited to five feet, and it is be- 

 lieved that after this total error has been distributed over the mile that 

 no point on the line is in error more than two or three feet. 



Owing to the lack of definite topographic changes and well-marked 

 lines of drainage, the use of form lines — that is, lines drawn in the 



