Late afternoon view across a more open part of Helen Allison Savanna. It's been a wetter than average summer and the lush grasses pictured here are testament to it. The mosquitoes also benefitted greatly from the wetter summer and were a serious nuisance on this visit.
Helen Allison Savanna is a Minnesota Department of Natural Resources Scientific and Natural Area, owned in part by The Nature Conservancy. The site supports a thriving oak savanna (mixed oak and grassland) that is home to a number of rare or uncommon woodland and grassland species of plants and animals.
This site is part of the Anoka Sand Plain, a large glacial outwash plain located north of the Twin Cities. While most of the sand plain is relatively flat, this area was reworked by wind and has some relatively large (for the area) sand dunes that probably formed mainly during the mid-Holocene dry period about 5,000 years ago. Some of the dunes are still mildly active today, with small blowout areas visible. The relatively steep topography probably saved this parcel of land from the plow.
The trees in the photo are bur oaks (Quercus macrocarpa) and other similar thick-barked, fire-resistant oak species. Fire plays a major role in establishing and maintaining most savanna ecosystems, killing off many species of trees and shrubs that would otherwise out-compete the native vegetation. Though mature, many of these trees only stand 15 to 20 feet high due to the limited water and nutrient status of these sandy soils. Some ash trees are also present on site.
DNR Scientific and Natural Areas are protected lands that have limited access to the public. Please see the Minnesota DNR SNA website for further information.