The Relation of Cladonia Mats to Soil Moisture 



Ci:i)KU I.. I'OKTICK AND MaKJOKIK 1.. W'OOI.I.ETT 



During the course of study of the establishment of seedlings 

 in cladonia and moss mats, data on soil moisture were obtained 

 thru the snmmer of 1927. The areas under observation are 

 located in the northern end of the southern peninsula of 

 Michigan near the I'niversity of Michigan Biological Station. 

 The soil is glacial sand. The areas were originally covered by 

 a dense forest of white^and Norway pines, Finns strobits and 

 Finns resinosa. Following lumbering and repeated fires, they 

 are now o\ergrown with aspens dominated by Fopnliis grandi- 

 dentata and bracken fern, Fteris aquilina. Where gaps appear 

 in the \egetation, the soil is loose and sandy. In many such 

 places large beds of almost pure Cladonia rangiferina are fre- 

 quently found. These, for the most part, occupy open places 

 nearly or quite unshaded by the surrounding trees. Seeds of 

 herbaceous and wood>- plants are available in abundance, but 

 seedlings usually fail to become established in Cladonia beds. 

 The moisture content of open surface soil is very low. Often 

 no moisture may be detected. The summer of 1927 was quite 

 ordinary with but one short period of high temperature and the 

 usual succession of fair, dry weather and light rainy days. 

 There were no thoroughly dry periods, consequently the soil 

 moisture during this year was reasonably favorable for the 

 establishment of seedlings, yet the establishment as usual did 

 not follow. 



The soil moisture was determined by the alcohol method of 

 Bouyoucos* which briefly is a mixing of the soil with alcohol 

 of known water content according to a definite plan and as- 

 certaining by a hydrometer the water content of the alcohol 

 after the mixing and multiplying by the factor which exper- 

 ience has shown proper. The samples were taken at the be- 

 ginning and during rain storms to show particularly the effect 

 of the Cladonia mat upon the soil moisture beneath it. Samples 

 were often taken at short intervals during the course of the 

 rain storm. 



* Bouyoucos, G. J. Rapid determination of soil moisture by alcohol. 

 Science, 65: 375, 1927. 



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