114 College of Forestry 
in the course of agricultural development, clearing the land 
began with the better drained areas and patches of swamp 
forest were left (though lumbered of course) on land too 
wet to be tilled. Cleared wet lands reverted to marsh- 
meadow and where willows and alders occur — as _ espe- 
cially along the stream channel leading into such swamps — 
the reversion has again reached the shrub stage and very 
commonly also the stage of invasion by white cedar, soft 
maple, ete. 
Effect of the Swamp Forest upon the Substratum. 
The mere mechanics involved in the erection and support 
against storm-stress of massive tree trunks with their spread 
of crown entails a profound effect upon the ground in which 
they are anchored. As pointed out before, it means the 
penetration of the soil by the proportionally massive root 
system. But where the substratum is built upon of organic 
stuff chiefly and is habitually saturated, owing to the high 
water table, the root system does not penetrate deeply — 
develops, rather, superficially and with wide reach and 
strongly emphasized buttressing effect. This brings about 
a rapid and unequal elevation of the land. It is in a way the 
mechanical problem of marsh vegetation over again, only the 
tussocks and the ‘‘ woven mat” are on a correspondingly 
bigger scale. For example, the elevation about a giant white 
pine as shown in Fig. 15 may be three or four feet above the 
general swamp level. So in traversing a swamp forest, say, 
in a wet season, the built-up frame work will be found to le 
well above water level and the intervening spaces below it. 
Later, as the water lowers, these latter will be exposed muck, 
but subject to invasion by mosses, liverworts, marsh annuals, 
ete. This rapid and uneven upbuilding of the swamp land is 
further accelerated by the accumulation of fallen trunks and 
particularly by the turning up of roots and soil when an old 
