HARPER: PLANT POPULATION OF MICHIGAN 35 
are quite characteristic, and the vacciniums are rare or absent. 
A hardwood area after logging, and even after the slash is burned, 
is very disagreeable to traverse, on account of the numerous logs 
and tops cumbering the ground, many of the logs being held up by 
stiff branches at such a height that it is just as hard to climb over 
them as to crawl under them, and only the smaller branches are 
consumed by fire, the larger ones making veritable chevaux-de- 
frise that last for many years. (Ten or twelve degrees farther 
south fallen trees decay much more rapidly, and do not materially 
impede the explorer after two or three years.*) 
Farmers have damaged the vegetation still further by totally 
eradicating much of it to make room for crops. This influence has 
been chiefly concentrated on the hardwood land, on account of its 
richer soil, but only about 17 per cent. of the area was classed as 
“improved land” in 1910. The extension of farms ought to have 
one indirect beneficial effect on the pine land, however, by multi- 
plying the barriers to fire and thus diminishing its frequency at 
any one point. 
Plant census.—The following plant list is based on the writer’s 
observations in northern lower Michigan between June 28 and 
August 24,1912. Although only nine of the twenty-one counties 
were visited in that time, the results are probably representative 
enough, except for the dunes and cliffs along the Great Lakes, which 
were not examined. The relative abundance of the species has 
been determined in the manner explained in several previous papers 
which are easily accessible.{ Although some may question the 
accuracy of my rapid reconnoissance methods, there i is probably 
no one at the present time in a position to assert that the results 
*In this connection see W. — Long, Investigations of the rotting of slash in 
Arkansas. U.S. Dept. Agr. Bull. 496. Feb. 1917. 
naomminmas’ —— however, aisaws degrees farther south the tropical hard- 
subject to fire at long intervals, followed 
Mah a few characteristic fireweeds (Trema, Carica, etc.), and are just as disagreeable 
to traverse for some time afterward as these Michigan forests, on account of the 
hardness and durability of the wood of many of the trees 
} For an a account of the effects of pare on fire frequency in the 
Ozarks, see Marbut, Field Operations U. S. Bur. Soils 1911: 1740. 1914. (Or page 
20 of the separates.) 
¢ Ann. Rep. Fla. Geol. Surv. 6: 177-180. 1914; Bull. Torrey Club 41: 557-559- 
1914; 44: 47-50. .1917; Torreya 17: 1-2, 5-6. 1917. 
