Biomass and productivity of the woody strata of forested bogs in northern Minnesota

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Abstract
Biomass and net primary productivity of three forested perched and three forested raised ombrotrophic bogs were determined and compared. The tree stratum was dominated by Picea mariana (Mill.) B.S.P. and the low shrub stratum by Ledum groenlandicum Oeder and Chamaedaphne calyculata (L.) Moench. Based on a modified forest growth and yield model (STEMS), aboveground living biomass of the tree stratum on the perched bogs was declining by about 0.5 t ha-1 year -1 from a base of 100.7 t ha-1, and on the raised bogs it was increasing by 0.2 t ha-1 year-1 on a base of 31.0 t ha-1. Net primary productivity of that stratum was 3.1 and 1.0 t ha-1 year-1 on the perched and raised bogs, respectively. Low shrub aboveground productivity, equal to mortality, was 0.4 and 2.0 t ha-1 year-1 on the perched and raised bogs, respectively. This was about 40% of the standing biomass of shrubs in both bog types. Aboveground net primary productivity of woody strata was 3.5 and 3.0 t ha-1 year-1 on the perched and raised bogs, respectively. These data are comparable to earlier estimates of Sphagnum production on the same bogs: 3.8 t ha-1 year-1 on perched bogs and 3.2 t ha-1 year-1 on perched bogs and 3.2 t ha-1 year-1 on raised bogs. Vascular herbs contributed an additional 0.2 t ha-1 year-1 to aboveground production on the perched bogs and 0.1 t ha-1 year-1 on the raised bogs. The higher productivity of perched bogs is probably related to slightly higher nutrient status related to their landscape position. The total productivity of all strata of these ombrotrophic sites approaches that of upland sites in the same region.