[LLOYD & scarth] BOG-FORESTS OF MEMPHREMAGOG 47 



suggesting a climax of destruction about that date; but measurements 

 of annual rings in a large number of tree trunks of all ages gives a 

 complete and graphic record of the struggle with environment. The 

 method was to measure the radial increase in 10 year periods, taking 

 an average radius, or, if necessary, more than one, in each tree. 

 Error due to variation with age is largely eliminated by the greatly 

 differing ages of the trees. 



Tree growth in Barton and Cherry River swamps. — Average radial 

 increment in millimeters of coniferous trees (8 tamaracks, 8 cedars, 

 and 1 pine), of ages varying from 30 to 300 years, and of ash trees 

 (40 to 130 years old) during ten year periods ending: 



It will be seen from the table that the rate of growth began to fall 

 ofï about 70 years ago and fell most, rapidly about 30 years ago — i.e., 

 at the same time that (from evidence of coastal erosion) the spring 

 floods were at a maximum. The decrease has slowed down since then 

 in the case of coniferae in general, and has even been followed by an 

 increase in the case of ash trees. 



Cause of the destructio?z. — A comparison with the dates of erection 

 of the various dams at Magog (1834, 1882 and 1914), while it does not 

 eliminate the possibility of the 1882 dam having some effect, strongly 

 indicates some other agency, especially since, as we have seen, it is 

 the fîood level and not the summer level that is, or has been, exces- 

 sively high. 



Precipitation records of the past 45 years- yield no evidence of 

 any marked correspondence between either the total annual fall or 

 the effective winter plus spring precipitation and tree growth. 



There remains the factor of deforestation, assisted by artificial 

 drainage, which is well known to cause increased seasonal fluctuations 

 in the levels of stream and lake. The curve of tree growth harmonizes 

 well with the probable rate of removal of the forest covering,^ at first 

 gradual, reaching a climax over 30 years ago, and more recently 

 balanced by new growth. 



^McGill University records, and also Richmond, Que., as far as available. 

 'No actual records being available, we take general opinion from various 

 sources at its face value. 



