Month: March 2024

Siding With The Grasses

As mentioned in the previous post, I was in Omaha a week ago.  After conducting my business, I planned to treat myself by visiting Neale Woods to see the slice of tallgrass prairie the naturalists at Fontenelle Forest were restoring.  Upon arrival, I was momentarily disappointed to discover that the grassland and much of the woods had been put to the torch only a couple of weeks earlier.

I say momentarily disappointed, but I’d add a naturalist’s delight.  This was an opportunity to get a better look at the efforts to recover a corner of prairie from a century and a half of neglect.

The prairies and oak savannas of the Midwest, like the pine savannas of the Southeast, are by their nature constantly under threat from ecological succession.  Shrubs and trees push towards the interior in a never ending campaign, threatening to block the sunlight from all vegetation laying closer to the ground.  Fire – from lightning and anthropogenic sources – was always the prairie’s greatest weapon of defense and conquest in what Aldo Leopold termed the “prairie war” between grassland and forest.  When the sodbusters began plowing the dark prairie soil to grow crops, they also banished fire from the uncropped land – for fire endangered buildings and livestock, not to mention the trees that offered their wood to the settlers and later to industry.  And so it was that many oak savannas, through deliberate fire exclusion and general neglect, grew thick canopies — stealing sunlight from the grasses and forbs that needed it. 

The prairie lost all the land that could be farmed.  Without its ally, fire, it surrendered the rest to the forest.   Even the oak savannas, a neutral ground of sorts where grasses and trees coexisted, reverted to forest as less fire-tolerant tree species crowded in to create closed-canopy forests. Of the 50 million acres of oak savanna existing in the middle reaches of the United States and southern Canada prior to European settlement, only around 30,000 acres remain in scattered pockets.

However, the pendulum is shifting back a fraction. In recent decades, knowledge of the elements and interactions of this hybrid of prairie and woodland community have been joined with a will to preserve or recreate said hybrid. 

In Neale Woods, it began with the setting aside of loess hills ill-suited for farming. Then came the restocking of prairie plants in openings in the tree canopy.  Now as I looked around, I saw evidence of the continuing efforts to create an open oak savanna.  Low stumps, which would have been hidden by tall grass but were easily seen in the ash, showed the ecologist’s direct interventions against individual trees.  Larger trunks, though still standing, were neatly girdled – not indiscriminately, only individuals or small clusters, just at the margins of existing openings.  And of course, there was prescribed fire, free to do its work within the confines of subtle firebreaks.  It burned away leaf litter, scarifying forb seeds and exposing bare soil for the next generation of ground cover.  Some tree seedlings died, others were topkilled.  Fire found chinks in the bark armor of some older trees, burning deeper wounds. 

Girdled trees

Sounds catastrophic, perhaps.  But for the flora and fauna adapted to fire long before the axe or plow made their marks, fire is a part of life – a trial to be periodically overcome but which leaves the survivors in better shape.  The larger bur oaks are nearly impervious to the low-running grass fires and were scarcely troubled; they will have less competition for roots and perhaps for sky.  The mountain mint and bloodroot, the beebalm and bluestems will grow vigorously.  Wildlife, including the rabbit whose droppings I saw by the trail or the wild turkeys that I watched foraging for baked acorns and roasted insects, make use of the invigorated ground cover.  Nectar-feeders, from monarch butterflies to longhorn bees, will fill the air come summer, as will the songbirds who arrive to feed in the humming air above the prairie.  The blackened crowns of the native grasses were already sprouting green sprigs, promising a return to tall grasses waving in the summer wind.

I commend the biologists and their supporters who are bringing back the oak-grassland savanna in this corner of Nebraska.  In the war between forest and prairie, these conservationists have sided with the grasses.

Additional Information:

News report on this fire

A view of Neale Woods in October

A brief view during the growing season.

Fontenelle Forest, stewards of Neale Woods.

The Inland Dunes on the Missouri

Last week I explored a couple of parks near Omaha, Nebraska, and thought I would take a couple of posts to talk about them.

West of the Missouri River and in the Great Plains region, you may expect unvaried topography.  Yet in Neale Woods Nature Reserve I found myself 200 feet above the nearest cornfield, on what was likely a thousand-year-old dune made of loess.

In geological terms, loess (pronounced “luss”) is material transported and deposited by aeolian (wind) action, consisting predominantly of silt-sized particles. The most familiar source of loess would be from the combination of drought and poor farming practices that became known as the Dust Bowl in the 1930s. However, the hills I stood on and the larger ridges across the river have an older and more distant origin.

The Loess Hills across the Missouri River in Iowa.

As glaciers and ice sheets expanded across the landscape during the last hundred thousand years, the accumulated weight of ice scoured earth down to bedrock, grinding away stone and carrying the powdered rock along with it.  During warmer periods, the ice retreated, with melt water transporting the “rock flour” downstream. Eventually, the silt settled into glaciofluvial mudflats. Much later, this floury dust dried, to be picked up by the wind (becoming loess) and carried aloft for hundreds or thousands of miles before coming to rest in blankets across much of the Midwest and down to the Gulf of Mexico (map).  There are other sources of loess, including dust blown in from deserts, volcanic fields, or other sites with fine particles and the wind to carry them.  The upper layers of loess in Nebraska likely come from deserts or perhaps previous loess deposits, sent windborne again as local climates fluctuated.  This deposition formed high dunes of silt and fine sand, and dates to between 1000 and 11,000 years ago.

Loess tends to have a high mineral content which, with some weathering and centuries of extraction by plant roots, creates exceptionally fertile soil.  This is one reason for the productivity of the Midwest and Great Plains. Unfortunately, loess is highly erodible by wind or water, and without a thick prairie sod to protect it, tons of fertile soil are lost on each farmed acre every year.

Notice the dark layer of organic topsoil

While easily eroded, loess tends to maintain vertical integrity provided there is some protection at the top.  That may explain why I came across these cliff faces.  Where Man’s desire for level roads conflicts with dune topography, the hill gets shorn.  In more sandy terrain, that 20-foot wall would have slumped all over the road in short order.

Ranging up to 200 feet, these forest-covered dunes stand long and narrow, dissected by gullies. They might have eroded down to low berms if not pinned in place by oaks and prairie grasses. Whether for the dune geology or the prairie ecology, they are worth a look if you ever get out that way.

This ridgetop is only level for about 15 yards before sloping down either side
Soil profile at Neale Woods. Note quarter for scale.