2010 NORTHEASTERN NATURALIST 17(2):261–272 Vegetation of Hooper Branch Nature Preserve, Iroquois County, Illinois Loy R. Phillippe1, Mary Ann Feist1, Richard L. Larimore1, Daniel T. Busemeyer1,2, Paul B. Marcum1, Connie J. Carroll-Cunningham1, James L. Ellis1, and John E. Ebinger1,* Abstract - The Hooper Branch Nature Preserve is located in the extensive dune and swale topography of the sand deposits of northeastern Illinois. The plant communities present at the time of this survey were similar to those of pre-settlement times. The vegetation associated with the dunes had not been disturbed except for past grazing; the swales, in contrast, were drained and farmed before the area was dedicated in 1986. Dry and dry-mesic sand savanna was associated with the dunes where Quercus velutina (Black Oak) accounted for 75% to 97% of the importance value in the savanna. Carex pensylvanica (Pennsylvania Sedge) was the dominant ground cover species usually followed by Schizachyrium scoparium (Little Bluestem). In parts of the preserve that had been most recently burned, woody species were more common in the ground layer, with the most important being Q. velutina seedlings, Rhus copallina (Dwarf Sumac), and Rubus allegheniensis (Common Blackberry). A 3-ha flatwoods in the Preserve was dominated by Q. palustris (Pin Oak), which accounted for nearly 95% of the overstory. Introduction Sand deposits are common in the northern half of Illinois, accounting for nearly 5% of the land surface of the state (Willman and Frye 1970). Sand prairies and sand savanna communities were common on these sand deposits in pre-settlement times (Schwegman 1973). These sand deposits occur on glacial outwash plains associated with erosional events of the Wisconsin glaciation (King 1981, Willman and Frye 1970). One of the most extensive is the Kankakee sands in parts of Iroquois and Kankakee counties, IL, and adjacent Newton County, IN. This sand deposit remained after glacial Lake Watseka and Lake Wauponsee were drained about 14,500 years ago as glacial moraines and ice dams were breached, resulting in the Kankakee Torrent (Willman 1973). A few studies of the vegetation of the Kankakee sands have been undertaken. The pre-settlement vegetation of Iroquois County was studied by Hedborn (1984), while McDowell et al. (1983) described the composition and structure of the savanna communities of the Iroquois County Conservation Area, located just south of the Hooper Branch Nature Preserve (HBNP). More recently, Johnson and Ebinger (1992, 1995) studied the effects of fire 1Illinois Natural History Survey, Champaign, IL 61820. 2Current address - Golder Associates Ltd. 960-6th Avenue S.W., Calgary, AB, Canada T2P 3T1. *Corresponding author - jeebinger@eiu.edu. 262 Northeastern Naturalist Vol. 17, No. 2 on the vegetation of the sand savannas at HBNP. The present study was undertaken to determine vascular plant species composition and structure and the floristic quality of the overstory and ground-layer vegetation of the savanna and flatwood communities at the HBNP. Study Area The 195-ha HBNP is located in extreme northeastern Iroquois County, about 9 km northeast of the town of Beaverville (S13 T29N R11W) in the Kankakee Sand Area Section of the Grand Prairie Natural Division of Illinois (Schwegman 1973) (Fig. 1). Due to high species diversity and quality of the savanna communities, the HBNP was dedicated as a nature preserve in 1986 by the Illinois Department of Natural Resources. Before being purchased, most of the dunes had been grazed, while most of the low, moist areas between the dunes were in agriculture. Also, the east side of the preserve had been ditched in an attempt to drain some of the lower areas, including a flatwoods. Nearly 75% of the sand savanna at the HBNP was designated as “good quality” by the Illinois Natural Areas Inventory (White 1978). Vegetation management at the HBNP has consisted of trying to reduce water loss by not removing silt from the drainage ditch, allowing the agricultural fields to vegetate naturally, and using controlled burns to prevent woody encroachment. Due to the large size of the area, only part of the preserve is usually burned at any one time. To separate the two burn units, an east–west access road divides the HBNP into two nearly equal parts. Management south of this access road included annual burns between 1986 and 1988 and occasionally since then (1986, 1987, 1988, 1999, 2001). The area to the north of the access road was subjected to more evenly spaced burns (1987, 1992, 1994, 1998, 1999) (Eric Smith, Illinois Department of Natural Resources, Springfield, IL, pers. comm.). The HBNP is situated at the edge of former glacial Lake Watseka. These sands were reworked by wind, creating the dune and swale topography present today. The characteristic sand savanna and sand prairie vegetation became established during the Hypsithermal period about 8000 years ago (King 1981). The low areas between the dunes are situated on Watseka loamy sands, while the flatwoods is on Granby fine sandy loams. These poorly drained soils are derived from outwash sediments and are acid, peaty sand with a brown to black surface horizon. The dune soils are Oakville fine sands that developed from sediments and are well drained and have a dark grayish brown surface horizon (Kiefer 1982, Wascher et al. 1951). Climate at the HBNP is continental with warm summers and cold winters. Based on weather data from Kanakee, 30 km to the northwest, mean annual precipitation is 98.0 cm, with May having the highest rainfall (11.5 cm). Mean annual temperature is 9.9 °C, with the hottest month being July (average of 23.6 °C), and the coldest January (average of -5.7 °C). Frost-free days range from 141 to 206, with the average being 174 days per year (Midwestern Regional Climate Center 2007). 2010 L.R. Phillippe et al. 263 Methods During the growing seasons of 2001 and 2002, the HBNP was visited 10 to 12 days throughout each growing season. The plants species encountered Figure 1. Location of Hooper Branch Nature Preserve (HBNP) and Iroquois County Conservation Area located about 6 km northeast of the town of Beaverville, Iroquois County, IL. 264 Northeastern Naturalist Vol. 17, No. 2 were collected, their habitat recorded, and voucher specimens deposited in the Stover-Ebinger Herbarium of Eastern Illinois University, Charleston, IL (EIU) or the herbarium of the Illinois Natural History Survey, Champaign, IL (ILLS). Criteria for designating non-native species followed Mohlenbrock (2002) and Gleason and Cronquist (1991). Nomenclature follows Mohlenbrock (2002). The woody overstory was sampled during late summer of 2001. At five sites in the sand savanna communities, permanent transects 4 ha in size (100 m x 400 m) were located randomly along cardinal compass directions. Two transects were located north of the access road (last burned in 1999), and three to the south of the access road (last burned in 2001). Each transect was divided into 64 contiguous quadrats 25 m on a side for ease in surveying. In the Pin Oak flatwoods, a 1-ha plot (100 m x 100 m; 16 contiguous quadrats) was used to survey the overstory. In each quadrat, all living- and dead-standing woody stems ≥10.0 cm dbh were identified, and their diameters recorded. From these data, the living-stem density (stems/ ha), basal area (m2/ha), relative density, relative dominance, importance value (I.V.), and average diameter (cm) were calculated for each species. Determination of the I.V. follows the procedure used by McIntosh (1957), and is the sum of the relative density and relative dominance (basal area). Dead-standing stem density (stems/ha), basal area (m2/ha), and average diameter were also determined. Woody understory composition and density (stems/ha) were determined using nested circular plots 0.0001, 0.001, and 0.01 ha in size. The nested plots were located at about 25-m intervals along each line transect through each study area. A random-numbers table (single digit) was used to determine the number of meters the points of the nested plots would be to the right (odd-numbered plots) or to the left (even-numbered plots) of the transect line. Four additional 0.0001-ha circular plots were located 6 m from the center points along cardinal compass directions. In the 0.0001-ha plots, woody seedlings (≤50 cm tall) and all shrubs were counted; in the 0.001-ha circular plots, small saplings (>50 cm tall and <2.5 cm dbh) were recorded; and in the 0.01-ha circular plots, large saplings (2.5–9.9 cm dbh) were tallied. The ground-layer vegetation was sampled by randomly locating 50-mlong line transects in each study site. Along each transect, 1-m2 quadrats were located at 1-m intervals (n = 50/transect). Odd-numbered quadrats were placed to the right, even-numbered to the left. A random-numbers table (single-digit) was used to determine the number of meters the quadrat was placed from the transect line. Cover of each species was determined using the Daubenmire cover-class system (Daubenmire 1959) as modified by Bailey and Poulton (1968). All herbaceous species, but only woody plants that were less than 50 cm tall, were included in the analysis. Importance value was determined by summing relative cover and relative frequency. 2010 L.R. Phillippe et al. 265 Results Species diversity was relatively high, with 334 species of vascular plants encountered at the HBNP. Ferns and fern-allies are not common in Illinois sand areas, but nine species were encountered on the HBNP. As is typical of prairie and savanna sand areas in Illinois, the Poaceae was the most common family with 52 species, the Asteraceae was second with 46 species, while the Cyperaceae was represented by 21 species. Of the species encountered, 32 were non-native exotic species, about 10% of the flora. The state endangered Hypericum adpressum Bart. (Creeping St. John’s-wort), Persicaria careyi (Olney) Greene (Carey’s Smartweed), Rubus schneideri Bailey (Bristly Blackberry), and Viola primulifolia L. (Primrose Violet) were observed (Herkert and Ebinger 2002). Sand savanna The dry sand savanna occurred on the ridges and upper parts of the dunes, while the dry-mesic sand savanna was found on the lower dune slopes. In the dry sand savanna, Quercus velutina Lam. (Black Oak) was the dominant overstory species, but Q. alba L. (White Oak) was usually present in low numbers. In the dry-mesic sand savannas, White Oak was more common, but Black Oak was still the dominant overstory species. Four of the five transects (sites 1, 2, 3, and 4) were located in dry sand savanna, where Black Oak accounted for more than 85% of the I.V. (Table 1). In contrast, transect five was mostly on a lower dune slope and flat lowland (site 5). In this dry-mesic sand savanna, Black Oak accounted for about 75% of the overstory (I.V. of 151), while White Oak had an I.V. of 48 (Table 1). In the two northern transects (sites 1 and 2), last burned in 1999, deadstanding individuals averaged 11.6 and 11.4 stems/ha, respectively, and more than 95% of the individuals were Black Oak. In the southern transects (sites 3, 4, and 5), last burned in 2001, dead-standing individuals were more than twice as common (26.8 to 32.0 stems/ha), and again most were Black Oaks. Coppice individuals (multiple-stemmed trees) were common components of the sand savanna vegetation; in most study sites, coppice individuals exceed 25% of the stems/ha for White Oaks and Black Oaks (Table 1). At all study sites, the woody understory was diverse. Numerous seedlings and shrubs were commonly encountered. Black Oak accounted for most of the tree seedlings present, and averaged between 5600 and 11,300 stems/ha. Many were sprouts from old root crowns, but seedlings were also common. Other tree seedlings were mostly poorly represented, with the exception of White Oak at site five (dry-mesic sand savanna), where seedlings of this species averaged 5100 seedlings/ha. Shrubs were common, averaging 34,900 and 87,800 individuals/ha, but their diversity was relatively low. Rosa carolina L. (Pasture Rose) was most common (6000 to 31,400 individuals/ ha), followed by Rubus allegheniensis Porter (Common Blackberry), Rhus copallina L. (Dwarf Sumac), Rhus glabra L. (Smooth Sumac), Amorpha canescens Pursh (Leadplant), Corylus americana Walt. (Hazelnut), Salix 266 Northeastern Naturalist Vol. 17, No. 2 Table 1. Density by diameter class (stems/ha), basal area (m2/ha), relative density (rel. den.), relative dominance (rel. dom.), importance value (I.V.), average diameter (avg. diam.; cm), and percent of coppice growth (% cop) for each taxon, for the woody species recorded at the study sites, Hooper Branch Nature Preserve, Iroquois County, IL. Diameter classes (cm) Species 10–19 20–29 30–39 40–49 50+ Total #/ha Basal area Rel. den. Rel. dom. I.V. Avg. diam. % cop Site 1* Quercus velutina 60.0 21.5 20.0 14.5 14.4 130.4 9.629 85.7 88.0 173.7 26.7 13.4 Q. alba 14.0 3.5 0.3 1.5 2.3 21.6 1.297 14.1 11.9 26.0 22.6 19.8 Prunus serotina 0.3 - - - - 0.3 0.007 0.2 0.1 0.3 18.2 - Totals 74.3 25.0 20.3 16.0 16.7 152.3 10.933 100.0 100.0 200.0 Site 2 Q. velutina 71.5 25.8 17.8 14.5 15.1 144.7 9.985 94.6 95.5 190.1 25.8 25.5 Q. alba 5.8 0.5 0.3 0.3 1.3 8.2 0.461 5.2 4.4 9.6 22.7 46.9 P. serotina 0.3 - - - - 0.3 0.005 0.2 0.1 0.3 15.1 - Totals 77.6 26.3 18.1 14.8 16.4 153.2 10.451 100.0 100.0 200.0 Site 3 Q. velutina 89.5 51.5 27.0 7.5 6.1 181.6 9.425 96.9 97.8 194.7 23.2 31.6 Q. alba 1.8 1.0 - 0.3 - 3.1 0.105 1.6 1.1 2.7 19.6 80.6 P. serotina 1.5 1.0 0.3 - - 2.8 0.105 1.5 1.1 2.6 20.6 - Totals 92.8 53.5 27.3 7.8 6.1 187.5 9.635 100.0 100.0 200.0 Site 4 Q. velutina 29.0 51.3 53.5 15.8 5.7 155.3 12.077 91.7 92.7 184.4 29.6 39.2 Q. alba 6.3 4.3 1.0 1.0 1.6 14.2 0.949 8.3 7.3 15.6 26.0 42.3 Totals 35.3 55.6 54.5 16.8 7.3 169.5 13.026 100.0 100.0 200.0 Site 5 Q. velutina 21.3 26.5 27.3 14.5 5.6 95.2 8.139 77.6 73.4 151.0 30.5 26.1 Q. alba 11.5 4.8 3.3 2.0 5.3 26.9 2.931 21.8 26.4 48.2 31.0 24.5 P. serotina 0.5 - - - - 0.5 0.006 0.4 0.1 0.5 12.4 - Q. palustris 0.3 - - - - 0.3 0.003 0.2 0.1 0.3 15.9 - Totals 33.6 31.3 30.6 16.5 10.9 122.9 11.079 100.0 100.0 200.0 *Sites 1 and 2 were located north of the access road (last burned in 1999), and sites 3, 4, and 5 were located south of the access road (last burned in 2001). 2010 L.R. Phillippe et al. 267 humilis Marsh. (Prairie Willow), and Vaccinium angustifolium Ait. (Lowbush Blueberry). Relatively few small saplings (550 to 1800 stems/ha) or large saplings (20–50 stems/ha) were encountered, which gave the savanna an open appearance. The ground-layer vegetation of the sand savanna varied widely, depending upon past disturbances, time since the last fire, and the extent of shading. Carex pensylvanica Lam. (Pennsylvania Sedge) was always the dominant ground-layer species encountered, while other common herbaceous taxa included Schizachyrium scoparium (Michx.) Nash (Little Bluestem), Chamaecrista spp. (partridge pea), and Sporobolus clandestinus (Biehler) Hitchc. (Dropseed). Black Oak and sometimes White Oak seedlings were common, along with the shrubs Smooth Sumac and Common Blackberry, which were mostly sprouts from individuals that had been top-killed by fire (Table 2). Pin Oak flatwoods This small flatwoods is located at the southeast corner of the preserve. The woody overstory averaged 302 stems/ha with a basal area of 25.746 m2/ha (Table 3). Quercus palustris Muench. (Pin Oak) dominated and accounted for nearly 95% of the I.V. (188.6). The only other overstory species present were Nyssa sylvatica Marsh. (Black Gum) and White Oak. The woody understory was open—only 35 saplings/ha were encountered. Woody seedlings, however, were common and averaged 41,800 stems/ha; most were Pin Oak (35,000 stems/ha) along with scattered individuals of Sassafras albidum (Nutt.) Nees (Sassafras), and Ilex verticillata (L.) Gray (Winterberry). The groundlayer vegetation was sparse; bare ground and litter averaged 70.80% (Table 4). Common ground-cover species encountered were Carex stricta Lam. (Tussock Sedge), Pin Oak, and Calamagrostis canadensis (Michx.) P. Beauv. (Bluejoint Grass,) with a total of 40 taxa recorded for the quadrats (Table 4). Discussion Fire has been the management tool of choice in maintaining the sand savanna communities at the HBNP. Early studies by Johnson and Ebinger (1992) indicated that annual burns decrease tree seedling and shrub density, decrease woody species diversity, and increase the number of top-killed individuals. They also found that less-frequent burning accounted for high ground-layer species diversity and a higher frequency of some herbaceous species (Johnson and Ebinger 1995). Since these early studies, the number of management burns has decreased. Prior to the present study, the north side of the preserve was last burned in 1999, the south side in 2001. During the present study, savanna transects to the north of the access road (sites 1 and 2) had higher species diversity, more herbaceous species, and a smaller percentage of woody individuals in the ground layer (Tables 1, 2). In contrast, the savanna transects to the south of the access road (sites 3, 4, and 5) had lower species diversity, and more woody seedlings and shrubs in the ground layer. Of the individuals that had been top-killed in 1999, many 268 Northeastern Naturalist Vol. 17, No. 2 Table 2. Mean cover (% of total) and importance value (I.V.) of the ground-layer species encountered at the five sand savanna study sites in the Hooper Branch Nature Preserve, Iroquois County, IL. Also given for each site is the total number of species encountered in the plots and the average number of species per plot. Site # 1* Site # 2 Site # 3 Site # 4 Site # 5 Species Mean cover I.V. Mean cover I.V. Mean cover I.V. Mean cover I.V. Mean cover I.V. Carex pensylvanica 18.13 42.3 17.55 49.3 33.85 75.7 32.35 97.7 17.32 48.9 Schizachyrium scoparium 6.41 18.5 6.47 19.3 3.06 10.5 0.38 4.8 3.59 13.5 Chamaecrista spp. 4.56 16.1 0.70 9.2 0.80 10.3 0.27 8.9 0.62 7.1 Rhus glabra 3.98 10.7 1.50 4.4 - - - - - - Quercus velutina 2.10 9.0 2.79 12.5 4.44 15.4 6.09 26.5 7.79 25.5 Sporobolus clandestinus 2.12 7.4 2.32 10.7 0.09 1.6 - - - - Amorpha canescens 2.44 6.5 0.23 2.6 - - - - - - Solidago nemoralis 2.11 6.3 0.02 0.5 0.01 0.4 0.08 1.7 - - Euphorbia corollata 0.86 6.1 0.51 5.2 0.62 7.1 0.11 3.4 0.18 3.1 Rubus allegheniensis 1.66 4.9 3.46 11.1 0.12 0.9 0.18 1.9 5.36 17.9 Koeleria macrantha 1.06 4.7 0.09 1.2 - - - - - - Rosa carolina 1.28 4.6 0.40 3.4 0.68 7.6 0.35 8.2 0.73 6.2 Helianthus divaricatus 1.26 4.2 - - - - - - - - Dichanthelium oligosanthes 0.35 3.9 0.16 1.8 - - 0.02 1.1 - - Lithospermum carolinense 0.79 3.6 0.40 2.3 - - 0.49 3.6 0.01 0.4 Conyza canadensis 0.59 3.2 0.19 4.0 - - - - 0.02 0.7 Liatris aspera 0.68 3.2 - - 0.74 3.4 - - 0.02 0.7 Phlox bifida 0.46 3.2 0.05 1.4 - - 0.02 1.1 - - Helianthemum spp. 0.36 3.0 0.33 5.4 0.75 8.4 0.09 4.6 0.04 1.5 Lespedeza capitata 0.17 2.9 0.23 3.8 0.28 3.3 0.08 1.7 0.06 0.5 2010 L.R. Phillippe et al. 269 Table 2, continued. Site # 1* Site # 2 Site # 3 Site # 4 Site # 5 Species Mean cover I.V. Mean cover I.V. Mean cover I.V. Mean cover I.V. Mean cover I.V. Aureolaria pedicularia 0.78 2.5 2.10 6.2 0.66 2.2 0.30 1.2 - - Viola pedata 0.38 2.5 0.09 1.2 - - - - - - Euthamia graminifolia 0.28 2.3 0.07 0.6 - - - - 0.05 1.9 Dichanthelium villosissimum 0.28 2.3 0.17 3.5 0.11 2.3 0.31 6.1 0.17 2.8 Rumex acetosella 0.18 2.1 1.56 5.8 0.04 1.5 0.01 0.5 0.16 2.4 Commandra umbellata 0.11 1.5 0.15 1.6 - - - - Tephrosia virginiana 0.42 1.4 2.32 6.9 2.73 8.2 - - - - Monarda puntata 0.32 1.3 0.34 4.3 - - - - 0.02 0.7 Rhus copallina 0.14 1.1 2.79 10.2 3.69 14.8 1.53 11.3 1.20 5.0 Hieracium scabrum 0.03 0.8 - - 0.03 1.2 0.06 3.0 0.28 3.3 Panicum virgatum 0.12 0.6 - - 0.14 3.4 0.06 0.6 0.13 1.3 Rubus flagellaris - - 0.08 1.0 4.35 11.0 0.42 2.5 0.01 0.4 Sorghastrum nutans - - 0.30 0.9 0.30 0.9 - - 0.95 7.7 Desmodium obtusum - - - - 0.18 1.4 0.01 0.5 0.49 2.7 Quercus alba - - - - 0.12 0.9 0.60 2.4 8.66 21.4 Rubus hispida - - - - - - - - 6.21 14.5 Others 2.46 17.3 0.97 9.7 0.53 7.6 0.33 6.7 0.79 9.9 Totals 56.87 200.0 48.34 200.0 58.32 200.0 44.14 200.0 54.86 200.0 Average bare ground 40.84 46.46 39.28 48.90 40.45 Total species 58 44 32 31 32 Averages species per plot 9.14 7.78 5.64 4.08 5.68 *Sites 1 and 2 were located north of the access road (last burned in 1999), and sites 3, 4, and 5 were located south of the access road (last burned in 2001). 270 Northeastern Naturalist Vol. 17, No. 2 had died, and those remaining were more than 50 cm tall and not included in the ground-layer survey. The high species diversity in the area that was last burned in 1999 is probably the result of the lag-time necessary for some species to recover from the fire, and for others to seed into the area. The savanna to the south of the access road had more than twice the number of dead standing individuals of Black Oak and White Oak as the area north of the access road. The increased fire frequency and possibly hotter Table 4. Frequency (%), relative frequency, average cover, relative cover, and importance value (I.V.) of the ground layer species encountered in a Pin Oak flatwoods, Hooper Branch Nature Preserve, Iroquois County, IL. Species with an IV of 1.0 or less are not included. Avgerage Relative Relative Species Frequency % cover frequency cover I.V. Carex stricta 62 9.22 15.7 35.1 50.8 Quercus palustris 68 4.43 17.3 16.9 34.2 Calamagrostis canadensis 30 5.02 7.6 19.1 26.7 Doellingeria umbellata 10 1.42 2.5 5.4 7.9 Erechtites hieracifolia 24 0.17 6.1 0.6 6.7 Sassafras albidum 16 0.47 4.1 1.8 5.9 Rubus hispidus 14 0.61 3.6 2.3 5.9 Quercus alba 10 0.73 2.5 2.8 5.3 Ilex verticillata 10 0.68 2.5 2.6 5.1 Apios americana 10 0.54 2.5 2.1 4.6 Rubus allegheniensis 8 0.67 2.0 2.5 4.5 Eupatorium serotinum 14 0.17 3.6 0.6 4.2 Solidago canadensis 6 0.66 1.5 2.5 4.0 Bidens frondosa 12 0.21 3.0 0.2 3.2 Dichanthelium acuminatum 10 0.15 2.5 0.6 3.1 Boehmeria cylindrica 10 0.05 2.5 0.2 2.7 Conyza canadensis 10 0.05 2.5 0.2 2.7 Persicaria punctatum 8 0.04 2.0 0.2 2.2 Potentilla simplex 6 0.08 1.5 0.3 1.8 Nyssa sylvatica 6 0.08 1.5 0.3 1.8 Vaccinium angustifolium 2 0.30 0.5 1.1 1.6 Lycopus americanus 6 0.03 1.5 0.1 1.6 Rubus flagellaris 4 0.12 1.0 0.5 1.5 Rubus occidentalis 4 0.12 1.0 0.5 1.5 Agrostis scabra 4 0.02 1.0 0.1 1.1 Others (15 species) - 0.92 8.0 1.4 9.4 Totals 26.96 100.0 100.0 200.0 Average ground cover 70.80 Table 3. Density by diameter class (stems/ha), basal area (m2/ha), relative density, relative dominance, importance value, and average diameter for the woody species recorded for the Pin Oak flatwood, Hooper Branch Nature Preserve, Iroquois County, IL. Diameter classes (cm) Total Basal Rel. Rel. Avg. Species 10–19 20–29 30–39 40–49 50+ #/ha area den. dom. I.V. diam. Quercus palustris 35.0 82.0 90.0 59.0 10.0 276.0 25.015 91.4 97.2 188.6 32.2 Nyssa sylvatica 16.0 2.0 1.0 - - 19.0 0.436 6.3 1.7 8.0 15.9 Quercus alba 3.0 3.0 1.0 - - 7.0 0.295 2.3 1.1 3.4 22.2 Totals 54.0 87.0 92.0 59.0 10.0 302.0 25.746 100.0 100.0 200.0 2010 L.R. Phillippe et al. 271 fires to the south of the access road in the late 1980s is probably responsible for this increase. Also, the number of coppice stems was mostly higher in the part of the preserve that had once been subjected to annual fires (Table 1). The Pin Oak flatwoods was usually flooded in winter and early spring due to an elevated water table. Though usually dry in summer and fall, standing water could occur at any time of the year. As a result, prolonged flooding is probably responsible for the low density of large saplings, though this could be the result of recent fires. This flatwoods showed indications of past cutting and de-watering. Most of the overstory individuals were in the 20–39 cm diameter classes. This finding suggests that it had probably been cut in the 1950s before the land was purchased by the state. Also, coppice stems averaged 23 stems/ha, accounting for 13% of the total basal area/ha (3.2 m2/ha). The average diameter of 32.2 cm for Pin Oak suggests a relatively young community. Previous studies of flatwoods in the Kankakee sands obtained similar results, with average diameters of 20.8 and 29.2 cm (McDowell et al. 1983). Few high-quality savanna communities are in public ownership in the Kankakee sands of Illinois. The majority of these occur on the HBNP and the associated Iroquois County Conservation Area. This complex, covering near 9.7 km2, contains many of the sand communities present in pre-settlement times in this part of the state. Management of this complex to maximize species diversity and community integrity is important. Presently, the draining of the eastern part of the preserve is having an impact on the vegetation of the Pin Oak flatwoods. By filling in the ditch, some of this problem will be solved. However, the loss of ground water due to draining efforts on the surrounding farmland will be a continuing problem. Presently, exotic species are not of major concern on the HBNP. Although 32 non-native (exotic) were collected, few were encountered in the natural communities. Most were found along the road surrounding the HBNP, in old agricultural fields, and on trails and dirt roads in the HBNP. Of the nonnative species found, only Achillea millefolium L. (Common Yarrow), Poa pratensis L. (Kentucky Blue Grass), and Rumex acetosella L. (Sour Dock) occurred in the quadrats. Of these, only Sour Dock was common. Management burns in the sand savanna communities appears to be suffi- cient to maintain the open nature of this community. The loss of plant species diversity due to the frequency of the burns is a problem. However, the two different burn cycles have kept the savannas open, as woody encroachment is not excessive. Also, without more detailed studies, we do not recommend any change in the management of the savanna community. Acknowledgments The authors would like to thank Dr. Gordon Tucker, Eastern Illinois University, for help with identification of the Cyperaceae, and Eric Smith, Natural Heritage Biologist, Illinois Department of Natural Resources for his help and advice. We would also like to thank the Illinois Department of Natural Resources for a Wildlife Preservation Fund grant to complete this study. 272 Northeastern Naturalist Vol. 17, No. 2 Literature Cited Bailey, A.W., and C.E. Poulton. 1968. Plant communities and environmental relationships in a portion of the Tillamook burn, northwestern Oregon. Ecology 49:1–13. Daubenmire, R. 1959. A canopy-coverage method of vegetation analysis. Northwest Science 33:43–64. Gleason, H.A., and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and adjacent Canada. 2nd Edition. New York Botanical Garden, Bronx, NY. Lxxv + 910 pp. Hedborn, E.A. 1984. The vascular flora of Iroquois County, Illinois. M.Sc. Thesis. Northeastern Illinois University, Chicago, IL. Herkert, J.R., and J.E. Ebinger. (Eds.). 2002. Endangered and threatened species of Illinois: Status and distribution. Volume 1. Plants. Illinois Endangered Species Protection Board, Springfield, IL. 161 pp. Johnson, K.C., and J.E. Ebinger. 1992. Effects of prescribed burns on the woody vegetation of a dry sand savanna, Hooper Branch Nature Preserve, Iroquois County, Illinois. Transactions of the Illinois State Academy of Science. 85:105–111. Johnson, K.C., and J.E. Ebinger. 1995. Effects of different fire regimes on the ground-layer vegetation of a dry sand savanna, Hooper Branch Nature Preserve, Iroquois County, Illinois. Erigenia 14:37–40. Keifer, L.M. 1982. Soil survey of Iroquois County, Illinois. United States Department of Agriculture, Soil Conservation Service, in cooperation with the Illinois Agricultural Experiment Station, Champaign, IL. vii + 184 pp. King, J.E. 1981. Late Quaternary vegetational history of Illinois. Ecological Monographs 51:43–62. McDowell, B., J. Newman, and J. Ebinger. 1983. Survey of the woody vegetation of the Kankakee Sand Area Section of Indiana and Illinois. Proceedings of the Indiana Academy of Science 93:187–193. McIntosh, R.P. 1957. The York Woods. A case history of forest succession in southern Wisconsin. Ecology 38:29–37. Midwestern Regional Climate Center. 2007. Illinois State Climatologist Office. Available online at http://mcc.sws.uiuc.edu. Accessed January 2007. Mohlenbrock, R.H. 2002. Vascular Flora of Illinois. Southern Illinois University Press, Carbondale, IL. xi + 490 pp. Schwegman, J.E. 1973. Comprehensive plan for the Illinois nature preserves system. Part 2. The natural divisions of Illinois. Illinois Nature Preserves Commission, Rockford, IL. Map + 32 pp. Wascher, H.L., R.S. Smith, and R.T. Odell. 1951. Iroquois County soils. University of Illinois Agricultural Experiment Station Soil Report 74:1–66. White J. 1978. Illinois natural areas inventory. Technical report. Volume I. Survey methods and results. Illinois Natural Areas Inventory, Urbana, IL. xix + 426 pp. Willman, H.B. 1973. Geology along the Illinois waterway—A basis for environmental planning. Illinois State Geological Survey Circular 478. Urbana, IL. 48 pp. Willman, H.B., and J.C. Frye. 1970. Pleistocene stratigraphy of Illinois. Illinois State Geological Survey Bulletin 94:1–204.