Omaha, Nebraska may be one of the most unlikely places to look for old-growth forest in the United States. The state’s largest conglomeration of asphalt and concrete, the city sits in the middle of a corn belt hundreds of miles wide, much of it growing out of old prairie soils. Omaha perches on a far narrower band of forest and woodland that the Missouri River’s floodplain and bluffs supported. Agriculture has eaten away most of that floodplain forest while the bluff woodlands have grown back and thickened following harvest. Concurrently, the Gateway to the West grew into the state’s largest city, and pavement replaced local forest.
However, Omaha also brought together a group of individuals who were both concerned about the loss of nature in the area and had the means to do something about it. They began Fontenelle Forest with a purchase of over 300 acres of forests on the bluffs in 1920. Much of that initial purchase was logged only selectively from the mid-1850’s to mid-1870’s, and dendrochronological investigations suggest that a couple of small, ridge top patches were never cut at all. Some later additions were farmed up until the 1960’s, but on a walk through the forest early tracts blend imperceptibly into the original purchase. Now tucked between the Omaha suburb of Bellevue and the Missouri River, Fontenelle Forest and Nature Center has grown to 1400 mostly forested acres split roughly evenly between the bluffs and the floodplain.
Twenty-six miles of trails run through the preserve’s upland and floodplain, and take visitors to oxbow lakes, foundations of Native American shelters, and rotating educational exhibits such as structures built from recyclables and life-size fiberglass dinosaurs detailed down to the wrinkles in their skin. Those shelters were built on the ridge tops in what would have been bur oak woodlands. The current trees’ woodland origins can still be seen in the branch structure of some of the oaks, and they have been dated back to 1732, but fire suppression has converted the woodlands into forest. American basswood, hackberry, shagbark hickory, and white ash have grown up around the old oaks in recent decades and hophornbeams filled in the understory.
Deep in the tallgrass prairie region, forest requires more than the fire-break provided by the Missouri River to survive. In the floodplain, the high water table counteracts the semi-arid climate, and on the bluffs deep deposits of wind-blown silt provide the moisture buffer. Those loess soils erode easily to produce narrow ravines that further concentrate moisture. Moving downslope, the bur oak quickly gives way to more drought sensitive northern red oak, and basswood and hackberry become more prominent in the overstory. Black walnut often dominates on the toe slopes and ravine bottoms, which also occasionally harbor colonies of Kentucky coffeetree. The herbaceous layer, while quite mixed on the ridges and mid slopes, undergoes a parallel transition down the moisture gradient. Drier slope positions feature many grasses and sedges while white snakeroot and finally wood nettle dominate the more moist and sheltered sites. While experiencing less fire than the ridges, that disturbance was not unknown in the ravines, and its absence may contribute to the complete lack of red oak and walnut regeneration and abundance of hackberry in the understory.
Altered disturbance regimes have also dramatically affected the floodplain forests. A patchwork of cottonwood, cottonwood-sycamore, and silver maple-green ash-white mulberry forests and oxbow lakes covers the floodplain. Those forests cover a continuum of ages from 60 to over 125 years, but younger forests are conspicuously absent. No logging occurred in the floodplain, so instead that distribution of ages reflects riverine processes. Historically, meandering of the river continually recycled the floodplain creating a patchwork of not only age, but also soil texture, and flooding frequency. In the 1950’s, hundreds of miles of the river in the Dakotas were converted to reservoir, and much of the main channel was lined with wing dikes. As intended, the river hasn’t moved since, and went 60 years between floods. An unintended consequence has been a scarcity of young cottonwood forest, which requires moist bare sand to establish, and the species associated with them are scarce up and down the river.
Flood control has also altered the species composition of the floodplain forests by allowing flood-intolerant species to colonize. While cottonwoods have persisted in the canopy, many species from the adjacent bluffs, especially hackberry, have filled in the understory and midstory. At least until 2011. That spring, a rain event in Montana triggered a flood that inundated much of the forest to depths of over five feet for two months. So many hackberries died that some pockets of forest were converted to woodland and other areas lost their midstory and understory. However, the flood also deposited enough sediment to spur patches of cottonwood and sycamore regeneration.
I didn’t know what I would see or measure when I visited Fontenelle Forest. Having only as much data about tree size across broad parts of the Midwest as Lewis and Clark did severally hampered NTS ability to look at east-west height and size gradients, and Fontenelle appeared to be a good place to start gathering data on many species. I had spent the entire summer sampling forests along 100 river-miles of the Missouri. Out of all those we sampled, Fontenelle looked like the most promising site for large trees, but I had seen only a small part of the floodplain and only driven through the bluffs. Several species, including sycamore and shagbark hickory, reach their northwestern range limit in the vicinity of Fontenelle, so the site would also help explore north-south size gradients.
Long time science manager Gary Garabrandt gave me a wonderful introduction to the site by taking his time on a drizzly fall day to guide me to the largest trees he knew of for several upland species. In each case, the trees he showed me were the largest I would see on my whole trip. In between trees, Gary shared his wealth of knowledge on the site’s history (and prehistory), and described ongoing efforts to preserve the site including erosion control, planting poorly regenerating species with local seed, and managing invasive species. Throughout the day, well-formed Kentucky coffee-trees kept catching my eye, but Gary just mentioned a large one further down the trail. When we finally reached that tree, I understood why Gary had shrugged at those other coffee-trees. This tree with picture-perfect form dwarfed every other coffee-tree I have seen, and set a new NTS diameter record for forest grown coffee-trees.
I spent the following two days exploring the ravines and floodplain trying to locate the largest diameter and tallest individual of each native tree species. Measuring on the bluffs turned out to be a bit of an adventure as walnuts would accelerate through 100’ of canopy space and then I would hear them crater into the duff a few feet away with a resounding thud.
The oldest section of floodplain forest impressed me the most. For work I had visited sites along the river that were mapped as forest in the 1890’s, but all of those other sites appeared more disturbed and less productive than this stand. Sycamores, growing in the harshest climate in their extensive range, matched the cottonwoods in height, and were gradually taking over the stand. The scattered cottonwoods, in the twilight of their lives, reminded me of tuliptrees in the Southern Appalachians with their massive branches and trunks commonly five feet thick. While measuring the cottonwoods and larger sycamores I was perplexed by a ridge of sediment about a foot high that extended south 10 to 20’ from the base of each trunk. I eventually realized that the trees were large enough that during the flood their trunks created an area of slack water downstream where sediment dropped out of suspension.
By expanding the range of NTS measurements, all of these numbers should help NTS investigate how climate and other broad scale factors influence tree height and growth. Paw paw, bitternut and shagbark hickories, redbud, white ash, sycamore, northern red oak, and rock elm in particular should prove valuable, because all of those species are growing near their northwestern range margin at the site. Of those, sycamore particularly impresses me for how tall the species is relative to other species and how little the height drops off approaching the species cold and arid range limits. Similarly, black walnut seems remarkable for the height the species can reach without access to a perennial source of water and relative to what the species reaches in more southern parts of its range. In addition to the coffee-tree, the downy hawthorn, peachleaf willow, and cottonwood are new forest grown diameter records for NTS.
However, the tallest cottonwood, 135.8’, made an even greater impression on me that the diameter record tree. The tree matches that height with an 18’3” cbh trunk, but what sets the tree apart is the massive crown. While dead branches and greatly reduced crowns show the decline of most of the older cottonwoods, the tallest tree’s crown remains full and healthy. The branch volume in that crown makes the tree clearly the largest at Fontenelle and a good candidate for largest tree by volume in the state.
I left feeling Fontenelle Forest is one of the great regional forests, like Cook State Forest in Pennsylvania or Congaree National Park in South Carolina. Those old-growth forests give us a window into the past. Parks named for the Lewis and Clark line the Missouri, but few if any of them can show what vegetation the explorers saw as well as Fontenelle can. The forest still faces pressures from fire suppression, flood control, and invasive species, and will change. However, managers are taking practical approaches that incorporate recent science to tackle these issues. Those efforts should help Fontenelle Forest retain its stature and integrity, and ensure future generations can still glimpse what Lewis and Clark saw.