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Study Area and Plot Network: The lands of the private Huron Mountain Club in northern Marquette County, Michigan, include ca. 1200 ha of old-growth mesic forests, dominated by Tsuga canadensis and Acer saccharum with several secondary species. The sample plot network described here consists of 313 plots placed at the nodes of a rectilinear grid (9.56 chain = 192.4 m spacing) where nodes fell within this vegetation of this description (several other forest types occupying significant portions of the area are not included in the sample. Plot centers were located by pacing and hand-held compass from the nearest point on the ground that could be located precisely on both areal photographs and topographic maps. Plots with centers falling within other vegetation types than old-growth hemlock-northern hardwood forest were excluded. Any plot whose center fell within qualifying forest, but overlapped into other vegetation types, or included more portions of lake or stream, included canopy gap > 50 m^2 in area, or was within 0.5 chains (33 feet) of trails or areas of selective cutting, was offset by the minimum number of half-chains along the cardinal direction opposite the avoided feature.

Plot vegetation sampling: Plots were circular and 450 m^2 in area.

Overstory stems -- stems of tree species of 9.0 cm or greater diameter at breast height (DBH = 4.5 feet) -- were tallied by species and DBH for all stems with centers within the full 450 m^2 plot. Trees forked below breast height were measured as multiple stems. Breast height was determined from upslope position; DBH was measured by tape. Canopy position (overtopped or in canopy) was recorded for all stems. Height of lowest live branch was estimated for Tsuga trees.

Understory tree stems -- stems of DBH 1.5-8.9 cm -- were tallied by species in three diameter classes (see data table) for the full 450 m^2 plot. Diameters were measure by ruler.

Ground cover -- Cover estimates for all herbaceous and shrubby species, and all trees > 1.5 cm DBH were estimated for a central 150 m^2 circulal sub-plot, centered within the larger plot. Cover classes are defined in data tables. First cover class indicates presence in the larger 450 m^2 plot but not in sub-plot. For tree species, cover was estimated separately for individuals < 50 cm and >50 cm tall (see data table). Spring ephemeral herbs were estimated at plot establishent in mid-May; other species were sampled in later summer 1988. 1988 was an unusually dry year and some species were severely wilted or browned; cover estimates included estimated cover before wilting. Cover estimation for lower cover classes was supported using a square frame = 0.1% of total sub-plot area.

Environmental sampling: For each plot a variety of environmental variables were measured or estimated. These are included in two data-tables.

Soil properties: Equal-sized samples of the surface organic soil layers and the upper 15 cm of the underlying mineral soil were collected at three locations in each plot (at the boundary of the inner subplot at azimuths of 0°, 120°, and 240°). Soil sample locations were offset from these positions if necessary to avoid pits, mounds, and woody debris. Thickness of organic horizons, and depth of the A horizon if present, were measured separately at these three sample locations, and means recorded. Soil samples were pooled by plot (organic and mineral horizons kept separate), air dried in the field, and returned to laboratory for measurements of texture, organic carbon (by combustion), and pH.

Topographic properties: Cover of coarse woody debris, pits and mounds, and rocks was estimated in the field. Slope and aspect were measured in field with compass and clinometer. Deer yard categories were derived from maps already held by the Huron Mountain Club from previous studies. Other variables were modeled or calculated using measured variables and map locations (using 1:24000 USGS topographical maps).

Geographic coordinates: Plots were originally placed by overlay of a printed sampling grid on enlarged copies of USGS 1:24000 USGS topographic maps. Distances to features recognizable on maps and on aerial IR photos were calculated, and used in the field to 'anchor' plot grids. Plot centers were placed by reference to these points and by pacing/measurement and compass. Latitude and longitude were measured on 4x enlarged USGS topographic maps with corrections calculated based on field-measurements.