Botanist Interior 43.1

118 THE MICHIGAN BOTANIST Vol. 49 TREE COMPOSITION AND DEMOGRAPHY OF A SECOND GROWTH HARDWOOD FOREST IN BERRIEN COUNTY, MICHIGAN Robert Tatina Dakota Wesleyan University Biology Department Mitchell, SD 57301 [email protected] ABSTRACT The tree species composition of a small, second growth forest in Berrien County, Michigan, about one-half mile east of Lake Michigan, was determined from tree numbers and diameters gath - ered using the T-square method. The forest is dominated by northern red oak ( Quercus rubra ), east - ern white pine ( Pinus strobus ) and red maple ( Acer rubrum ). When compared to upland sites, low - land sites had greater species diversity (14 compared to 11) and a greater basal area (57.84 compared to 39.16 m 2 . ha –1 ), but had a lower density (317.89 compared to 357.05 trees . ha –1 ) of trees. Size class structure of the tree species generally showed that they were replacing themselves and will con - tinue for some time into the future. KEY WORDS: Berrien County, Michigan, Southern Mesic Hardwood Forest, Species Compo - sition, Tree Size Classes INTRODUCTION According to original land survey records, the vegetation of Berrien County, Michigan, prior to settlement by non-native people was hardwood forest with dominance shared by American beech ( Fagus grandifolia ) and sugar maple (Acer saccharum ) (Brewer et al. 1984). Since then much of the county has been logged (Coolidge 1906) and some of it burned (Ellis 1880), leaving a mosaic of agricultural land, forests and commercial and residential developments. Over time, the once grand forests of Michigan have become reduced in area, and today represent about half of their former extent (Dickmann and Leefers 2003). Presently, most of the forested stands are second growth. Two forests in Berrien County have been the subject of continuing research. These are the beech-maple forest at Warren Woods State Park studied by Billington (1924), Cain (1935), Brewer and Merritt (1978), Woods (1979), Brewer (1980), and Donnelly and Murphy (1987) and the several forest types at Warren Dunes State Park described by Wells and Thompson (1982), Smith and Woodland (2006) and Smith and Woodland (2007). These have provided much insight into the composition and dynamics of old growth, hardwood forests as well as a benchmark against which to compare other forests. How - ever, most of the forests in southwestern Michigan, as well as the rest of the state, are second growth and young with little attention paid to their composi - tion and dynamics. 2010 THE MICHIGAN BOTANIST 119 This study was conducted in a small, second growth forest in southwestern Michigan about five miles north of Warren Woods State Park and within a half mile south of the woods at Warren Dunes State Park. Prior to sampling the trees, I compiled a list of 184 vascular plant species and from it estimated the Floristic Quality Index to be greater than 50. My objectives were 1) to describe the com - position of the forest in terms of its tree species and 2) to examine the size class (age) structure of the tree species to estimate what the composition of this forest might be in the future. STUDY AREA The study area (Figure 1) is a forested stand of approximately 8.1 ha, ~ 1 km WNW of Sawyer, Michigan. Its legal description is T7S, R20E, Sec. 2, NW 1/4, SW 1/4. On the south it is bounded by Lake Lane and on the west by Tower Hill Road. From the southwest corner, the area extends ~250 m N and ~400 m E. It is the southern end of the Tower Hill Camp and Retreat Center (THC), a 22-hectare tract which was donated to the Illinois Conference of the United Church of Christ by Edward K. Warren in 1923 (Gregg Briggs, THC Director, personal communication). The site is approximately 0.75 km south - east of Lake Michigan. Although I was unable to find specific information about the property prior to it being converted into a camp, circumstantial evidence suggests that the area was logged. In 1854 a saw mill was operating in Sawyer, and in 1861 there was another saw mill operating in the vicinity with a horse drawn railroad running through the area of the camp down to a pier on Lake Michigan at the Chikam - ing—Lake Township boundary (Coolidge 1906). These historical notes would suggest that the area had been logged as early as the mid 1800s. The age of the stand, estimated from tree cores of some of the larger red oaks, is about 70–80 years old. Immediately to the north of the stand is a white pine planting with trees standing in obvious rows. These trees were aged at 70–80 years also. The absence of sawed tree stumps indicates that the area had not been logged recently. In addition, there is no evidence of recent fire. The topography is rolling with small hills that peak at approximately 200 m above sea level and low areas at 190 m. The soils are sandy and have been mapped as Oakville fine sands on ridge tops, knolls and slopes and Pipestone sand and Grandby loamy fine sand on nearly level areas (Larson 1980). The Oakville fine sands have rapid infiltration rates, and the Pipestone sand and Grandby loamy fine sand are poorly drained because of a high water table (Lar - son 1980). Generally, the forest fits a southern mesic hardwood forest as de - scribed by Kost et al. (2007). METHODS During the summer, 2009, starting at the SW corner of the study area, I laid out a grid of sam - pling points 20 m in from the property lines and 20 m apart. From the resulting 250 intersecting lines, ~150 intersections were chosen at random to become sampling point centers. (Excluded from sam - 120 THE MICHIGAN BOTANIST Vol. 49 pling was a portion of the woods where white pines had been planted in obvious rows and marked as “Pines” in Figure 1.) To determine which two trees at each sampling point were to be measured, I fol - lowed the T-square plotless sampling method because it overcomes sampling biases when trees are not randomly distributed (Greenwood 1996). (I chose this method as an alternative to determining the actual distributional pattern of the trees.) Selecting the tree nearest a sampling point, I measured the distance between its center and the sampling point and then measured the circumference of the tree at breast height (1.4 m). Following the sampling procedures of Curtis (1959), I designated tree size class individuals as those that had a diameter at breast height (dbh) ≥ 10 cm. The second tree to be measured was the nearest neighbor to the first tree found beyond a line drawn through the first tree perpendicular to a line extending from the sampling point to the first tree. I then measured the distance between the first tree and the second tree, and measured the circumference of the second tree at breast height. Saplings (tree species whose dbh < 10 cm and whose height ≥ 30 cm) were counted by dbh size class (< 2; ≥ 2 < 4; ≥ 4 < 6; ≥ 6 < 8; ≥ 8 < 10 cm) in 0.01 ha circular plots (radius = 5.64 m) whose radii extended from each sampling point. Seedlings (< 2 cm dbh and < 30 cm tall) of tree species were counted in 0.002 ha circular plots (radius = 2.52 m) centered on the sampling point. I also noted whether the point and the sampling area were located in a lowland or an upland. Generally, the low - land points were located at the southern and eastern edges of the forest and had water standing in de - pressions in the spring, 2009. The uplands were on shallow slopes and hills and showed no evidence of having been inundated. Density of tree size class species was determined from distance measurements using the follow - ing: density = n 2/2.2828 ΣxΣy, in which n is the number of sampling points, x is the distance to the nearest tree from a sampling point and y is the distance from the first tree to its nearest neighbor (Greenwood 1996). For sapling and seedling species, density was calculated by dividing the number of individuals counted by the total area sampled. Tree circumferences were converted into basal areas and then summed by species; points of occurrence were converted into frequency by dividing the number of points of occurrence by the number of points sampled. Density, basal area and fre - quency for each tree size class species were relativized and then summed to produce importance val - ues (IV). With an increment borer I extracted cores at breast height from several larger trees. After drying the cores I counted the annual rings to determine the approximate age of each tree. Scientific nomen - clature follows that of Gleason and Cronquist (1991), and common names of trees that of Barnes and Wagner (2004). RESULTS Increment cores taken from seven species of larger trees produced ages that fell into two groups (Table 1). Except for Fagus grandifolia , which averaged about 125 years old, all of the other species were 70 to 80 years old. Table 2 shows the tree species composition for the entire forest. The stand had a total density of nearly 342 trees . ha –1 and a total basal area of 122.50 m 2 . ha –1 . The average distance between trees was 3.95 m ± 2.39 (sd). Based on IVs, dom - inant tree species were Quercus rubra (northern red oak ), Pinus strobus (eastern white pine) and Acer rubrum (northern red maple). Acer rubrum existed at the highest density (69.05 trees . ha –1 ).

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