A Rare Mixed-Oak Sand Flatwoods Community, Iroquois County Conservation Area, Illinois

Sand flatwoods communities dominated by Quercus palustris (pin oak) are occasionally encountered in the Kankakee Sands Region of the Grand Prairie Natural Division in northeastern Illinois. These communities are typically found in depressions subject to ponding from a seasonally high water table. Recently, a rare mixed-oak sand flatwoods community was encountered. This previously undescribed community type is slightly elevated above the typical sand flatwoods and therefore elevated above and influenced less by groundwater. The area is still largely flat but with slight depressions that collect rainwater. Here, Q. ellipsoidalis (Hill’s oak) dominates with an Importance Value (IV200) of 116.1, (200 possible), Q. palustris is also common (IV200 of 72.0), while Q. alba (white oak) is occasional (IV200 of 10.6). This community has a well-developed woody understory; seedlings and saplings of Q. ellipsoidalis and Q. palustris are very common along with the shrubs Vaccinium angustifolium (low- bush blueberry) and Aronia melanocarpa (black chokeberry). Mean cover of ground layer vegetation averages 80%. The dominant herbaceous species is Carex pensylvanica (Pennsylvania sedge). Overall, this unique community type had low species diversity, especially in the canopy and ground layer.