Biomass, structure, and trophic environment of peatland vegetation in Minnesota

The structure of peatland vegetation in Minnesota is affected by trophic conditions, the soil-water regime, and the disturbance history. Trophic conditions have a major effect on the species composition. Structurally, this results in the exclusion of most tall shrubs, hardwood trees, and forbs from ombrotrophic sites and a greater biomass of mosses and ericad shrubs on those sites than on minerotrophic sites. Classification of peatland vegetation into physiognomic groups provides reasonable estimates of total aboveground biomass. Trophic conditionsper se, however, have a minor effect on aboveground biomass; on both ombrotrophic and minerotrophic peatlands, biomass increases from less than 10 Mg ha−1 on the wettest sites to over 100 Mg ha−1 on the driest, undisturbed sites. Peatland sites that have comparatively dry, well-aerated soils support dense forests if they have not recently been disturbed; shrubs dominate on those sites after disturbance. Excessively wet sites are dominated by mosses (particularly on ombrotrophic peatlands) or graminoids (on minerotrophic peatlands). On ombrotrophic sites, the relatively dry conditions that lead to higher tree and total biomass also lead to lower pH resulting in an inverse relationship between biomass and pH.