The Origins, Spread, and Consolidation of a Floating Bog in Harvard Pond, Petersham, Massachusetts

Abstract

The mode of development of an extensive floating bog (400 m by 400 m) at the north end of Harvard Pond, an artificial lake, was studied by careful examination and local dissection of the bog mat within a 32—m by 16—m plot. Excavations were also made at the bog margin. The origins, spread, and consolidation of the floating mat are largely explained by the growth characteristics of one ericaceous shrub, Chamaedaphne calyculata (L.) var. angustifolia (Ait.) Rehd. A wetland forest was cut about 1830, and Chamaedaphne, first invaded the tree stumps between 1830 and 1890 (when they were located in a sedge meadow). Harvard Pond was formed about 1890, and the floating mat has developed between 1890 and 1968 (by the lateral spread of Chamaedaphne across the water surface to occupy the intervening spaces between stumps). Bog—advance rates were estimated from photographs and from annual growth increments for the shrub. Expansion appears to have been rapid (up to 6.3 cm/year or 2.5 inches/year).