Field Location Details
The experimental site is a bog within the Marcell Experimental Forest (MEF; N 47° 30.171’, W 93° 28.970’), which is located approximately 40 km north of Grand Rapids, Minnesota, USA. The MEF is within the Laurentian Mixed Forest Province, which is a transitional zone between boreal and broadleaf deciduous forests (McNab and Avers, 1996). The landscape is a typical moraine landscape of the Upper Great Lakes Region, and includes uplands, peatlands, and lakes. Peatlands at the MEF range in size from several hectares to several tens of hectares and may have forest, shrub, or sedge cover. The MEF has an extensive historical database of hydrological, chemical and meteorological measurements that document hydrological, biogeochemical, and ecosystem processes since the 1 960s (Nichols and Brown, 1980; Boelter and Verry, 1977; Verry 1981, Grigal 1991; Urban et al. 1989; Verry and Timmons 1982, for a complete list see http://nrs.fs.fed.us/ef/marcell/data/).
The climate is subhumid continental, with wide and rapid diurnal and seasonal temperature fluctuations (Verry et al. 1988). Over the period from 1961 through 2005 the average annual air temperature was 3.3°C, with daily mean extremes of -38°C and 30°C, and the average annual precipitation was 768 mm. According to Kolka et al. (1999), 75% of the precipitation occurs in the snow-free period from mid-April to early November (Verry et al. 1988). Mean annual air temperatures have increased about 0.4°C per decade over the last 40 years (http://nrs.fs.fed.us/ef/marcell/data/).
Within the 1141–ha MEF research area, the manipulation will be located in an ombrotrophic bog (a raised dome peat bog in which water and nutrient inputs originate from atmospheric sources). The study site at N 47° 30.476’; W 93° 27.162’ and 418 m above msl is designated S1. It is an 8.1-ha Picea-Sphagnum bog that was harvested in two successive strip cuts 5 yr apart (1969 and 1974, Verry et al. 1981). The bog surface has a hummock/hollow microtopography with a typical relief of 10 to 30 cm between the tops of the hummocks and the bottoms of the hollows (Nichols 1998). Soils are the Greenwood series (Typic Haplohemist) in the bog and the Warba series (Haplic Glossudalf) in the uplands (Soil Survey Staff, 1987). The peatland has well-decomposed acidic peat (pH ~4) to varying depths, is overlain by 30–1 00 cm of less decomposed peat, and has an average depth of 2.5 m (Boelter and Verry 1977; Nichols 1998).
The 25.1-ha upland surrounding the bog is dominated by mature Populus tremuloides Michx. and Betula papyrifera Marsh. Vegetation within the S1 bog is dominated by the tree species Picea mariana (mean height of 3 m in 1999, Kolka et al. 1999). The bryophyte layer on drier hummocks is dominated by various species of Sphagnum (S. angustifolium, S. capillifolium, and S. magellanicum; Verry 1984). Other bryophytes include Aulacomnium palustre (ribbed bog moss), Pleurozium schreberi (big red stem moss), and Polytrichum juniperinum (juniper polytrichum moss). The understory also supports a layer of ericaceous shrubs including Ledum groenlandicum Oeder [Labrador tea]), Chamaedaphne calyculata (L.) Moench. [leather leaf], Andromeda polifolia L. var. glaucophylla (Link) DC [bog rosemary], Kalmia polifolia (bog laurel), and Gaultheria hispidula [Creeping snowberry]. The bog also has graminoids Carex trisperma and Eriophorum spissum (cotton grass), as well as forbs Sarracenia purpurea (northern pitcher plant) and Smilacina trifolia (three-leaved false Solomon's seal).