Colors of Summer
Prairie wildflowers show off their hues
The MARIETTA SAND PRAIRIE is one of the botanical gems of all the land holdings managed by the Marshall County Conservation Board. It was always known as a special place with special types of native plants growing on a complex of unusual soils. In this case, the soils had a high content of fine sand. What grows on this 229 acre parcel must be hardy and unique or they will not make it. Considering that some of the species of grasses and forbs are remnants of ice age survival, that is a pretty good testament to the term hardy. Professional botanists have studied and surveyed the various plant species growing here. The list tops 200. And a fair number are really unique in that they fit the classification of threatened or endangered, in Iowa or nationally.
The Sand Prairie in located along Knapp Avenue, about 1.5 miles north of county road E-29 (Hartland Blacktop road). Or as the crow flies, the Sand Prairie is southwest of Albion two miles. The original land purchase happened in June, 1983. The late Janet Paterson was instrumental in this acquisition through her generous gift. Previous owners were Howard and Galdys Conrad. The Conrad’s farmed some of the lands and tried to make a living on it. However, the soils, from a crop production standpoint, were severely lacking. The original 17 acre acquisition was located at the far southwest corner of the farm. It was not cultivated. It was grazed occasionally but not intensively by cattle. To drive farm equipment on that segment meant you were in for a bumpy ride over pocket gopher mounds of sand. The risk of getting farm tractors stuck was also high due to wet spots that seemed to have no bottom.
If we travel way back in history, ecological and geological, one discovers that this vicinity of several square miles of uplands lying adjacent to the Iowa River flood plain and Minerva Creek’s floodplain was subjected to immense gale force winds coming off the Wisconsinan ice sheet that lay to the west. The time of maximum glaciation was about 15,000 years ago. Now fast forward to lets say to 10,000 years ago, the ice edge of the big north central Iowa Wisconsinan “thumb print” was eroding from a naturally warming climate. Ice was still in northern Iowa. 10,000 years ago, all of what is now Polk, Story, Boone, Webster, Hamilton and Hardin County was ice free. However ice free parent material of future soils were not well vegetated due to still dominant long, cold winters and very short summers. Tundra vegetation types were the first low growing plants to attempt to hold the soil.
Holding exposed soil was key. Strong winds whipped across this landscape. Anything capable of being swept up into the air currents was removed. Some of those soil particles were fine silts and sands. If a person was present at the time to witness this, most likely not, that must have been seen as huge dust-like clouds. This process of erosion by wind took place over many thousands of years. In the long run, as terrific strong winds moved sand about, drifts of sand dune like mounds accumulated. And this accumulation of sand was laid down on top of an ancient soil surface that at the time had its own plant life clinging to existence. This old but now buried ancient soil surface goes by the geologic name paleosol, meaning ancient soil surface. Where modern day farm operations may encounter this layer, their term for it is ‘hard pan.’ It is so highly compacted as to be impervious to water percolation.
As a side note, wind blown sands continued down the Iowa River valley during those thousands of years time. At upslope locations on the east side of the river valley, winds were forced upward by the hills paralleling the river. As winds hit those slopes, air currents were forced up. When wind changes direction like that, it slows down and now its strength to hold sand in suspension is lost. Fine grain sands fell out of the sky to accumulate to great depths along the east side of the valley. Today we know this vicinity as the Sand Road, that 6 mile long connection between Albion and Marshalltown along the east side of the river valley.
Now back to the history lesson. Mother Nature had set the stage for all of Iowa to go through a long series of plant successional stages after glaciers had melted through Minnesota and into Canada. Nature is going to make sure some types of plant life colonize any exposed soils. Rain, sunlight and minerals in those ancient parent material soils were primed to develop. Tundra vegetation dominated at first, followed by boreal forest of stunted spruce trees.
As the climate continued to warm and become drier, deciduous trees grew to replace spruce. And given more time and even drier climatic conditions, trees were less successful as grass types grew to dominate. For all the upper Midwest, tall grass prairie was the last ecological regime to greet settlers into Iowa in the mid 1800’s. And for thousands of years, plant life flourished, died, decayed, and prospered for many centuries, building top soil at about one inch per century. Add lot of centuries together and you can now picture the immense amount of time it took for thick rich black top soils to develop over the entire Midwest landscape.
Tall grass prairies were the major plant life land cover prior to settlement. About 85 percent of Iowa was prairie. Another 13 percent was forested lands and two percent was water in lakes or river systems. Once settlement’s forces were unleashed, Iowa’s prairies disappeared fast. The soil under the mat of grasses was rich and fertile, primed to become some of the best farm land in the nation. Native prairie land remnants are now less than one-tenth of one percent. A few Iowa State Preserves commemorate Iowa’s prairie past and serve as ecological and botanical benchmarks of the past. Loam soil prairies are the norm.
Sand soil based prairies are even more rare. And Marshall County has one of these ecological gems. It is the Marietta Sand Prairie. If you should venture out to make a hike into and through this prairie, do admire the flowers, admire the tall grasses and try to envision this vegetation type as dominant for as far as the eye could see. And now you can also reflect on the ecological and geological forces that brought it to be.