ECOLOGICAL RELATIONS OF THE FLORA. 



53 



the same apparent lack of plant food materials.f The soil at West 

 Olive is given as jack pine barren. It would thus seem that in the 

 determination of the factors responsible for the predominance of the 

 jack pine the poor mineral content of the soil must be considered. 



If Livingston is correct, the chief force in preventing the betterment 

 of the barrens is the fires which not only destroy all growth but 

 burn the small accumulation of humus as well. Beal (1888, p. 28) 

 has shown that jack pine seeds have great vitality and can last over 

 a great many years, which explains in a wa}'' the invasion and ecesis 

 in the burned over sections, for the seeds of many species falling on the 

 newh^ denuded area are not able to last over until a favorable time. 



It was observed at Sand Point that the sand dune could be rapidly 

 clothed by heath and sod and this in turn be replaced by jack pine 

 and scrub oaks. With these trees the humus building is very slow, 

 but the sod formed by Poa compressa and the gradual accumulation 

 of humus after a time enables Pinus resinosa to replace the jack pine. 



tAnalyses of Soil Water from W. Olive, Michigan, made July 25, 1904. 

 (Analyses furnislied by Prof. F. S. Kedzie, Michigan Agricultural College.) 



* Analyses of Soil of Jack Pine Barrens. 



Sample 1 is from Airgin soil from experimental farm at Gra3iing (in Jack Pine plains). 

 Samples 2 ami 3 are from fields which have been cultivated and had various green crops 

 (legumes) plowed under for three years. 



.\dapted from Kedzie, R. C. Mich. Agr. Sta. Bull. 99. 



