Sphagnum production in forested bogs of northern Minnesota

Annual production of Sphagnum on three perched and three raised forested bogs was determined and compared. Perched bogs occupy small depressions in glacial moraines and raised bogs occur on broad, flat plains. Data from both cranked rods and threads were used with regression techniques to determine rates of growth on hummocks and hollows of bog microrelief. Hummocks and hollows were operationally defined by the characteristic moss species that dominated each position. Over a 3-year sampling period, average rate of moss growth in perched bogs was 3.9 (± 4%) on hummocks and 13.1 cm year −1 (± 13%) in hollows. In raised bogs, the growth was 3.6 (± 4%) and 9.1 cm year −1 (± 14%), respectively. About half the lineal growth occurred early in the growing season, and slightly more of the remaining growth occurred in midseason compared with late season. Conversion to ovendry mass per unit surface area of bog indicates production of 320 on hummocks and 520 in hollows on perched bogs; 300 on hummocks and 370 g m −2 year −1 in hollows on raised bogs. Because of the hummock–hollow microrelief, total surface area occupied by moss is about 35% greater than the vertically projected area of the bog. Final estimates of Sphagnum production per unit vertically projected bog area, taking this information into account, were 380 (± 19%) on perched bogs and 320 g m −1 year −1 (± 19%) on raised bogs.