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Bur Oak Symposium
There were studious experts, analytical academics, dedicated arborists and those who just love trees. Their common denominator was their curiosity about "Bur Oak Canyon."
The "Bur Oak Symposium," hosted Sept. 8 and 9 by Common Scents and McCook Community College, attracted a wide array of people from nine states wondering how a stand of bur oak trees has grown and survived thousands of years in a canyon in remote Hitchcock County in Southwest Nebraska.
The stand of trees follows a creek bed in a two-mile canyon southwest of Culbertson, near the Kansas-Nebraska state line, and is believed to be the only large stand of native bur oak trees within a 200-mile radius.
Bur oak trees are planted as landscape trees quite often in the Midwest, because they like full sun, grow in all types of soil and are drought and disease resistant. So specimen trees are not uncommon. But a stand of 300 to 400 bur oak trees? A stand that's been there for hundreds and hundreds of years?
In the deep canyon whose east and west rims are fringed by oak leaves and studded by burry acorns, bur oaks have grown and regenerated with little influence by and only nominal interference from man. Speakers at the symposium analyzed the tree stand -- how they got there ... who may have utilized them ... how they will live into the future ...
Tim Buchanan, city forester for Fort Collins, Colo., told those gathered for the symposium that during the ice age, Nebraska was very cold and covered by glaciers. Ten thousand years ago, temperatures began to approach those more similar to today's, creating a habitat suitable for migration north of plant life.
In the last 9,500 to 10,000 years, Buchanan said, the environment warmed up and humidity patterns changed, and oaks advanced their range from the Gulf Coast north and northwest, even into Canada.
Hot, dry periods 5,000 years before present stressed oak populations and their environment, and the oak savannah shifted to the east. "Is Bur Oak Canyon a relict population that survived the savannah shift?" Buchanan asked. Is Bur Oak Canyon "relict" -- left behind in a process of change? "Most likely, Bur Oak Canyon is a hold-out that survived that dry period," Buchanan said.
Bur Oak Canyon is a great example of adaptation to changes in climate and nature, Buchanan said. Surviving is all about adaptation, he said. The oaks grow well in the canyon's open grassy areas, in niches in its limestone cliffs and outcroppings, up into its gulches and along the creek bed. Roots of some trees have been exposed by soil erosion caused by gully-washers, Buchanan said, and root tissue on "octopus" trees has become stem tissue with bark.
There is evidence that areas of the tree stand have survived fire.
Bur oaks have remarkable deep tap roots, enabling them to survive drought. The biomass of a bur oak, Buchanan said, is 50-50 above and below ground. "It puts a lot of energy into root growth," he said.
There is also evidence in Bur Oak Canyon of hybridization by other species of oak trees, Buchanan said, as the trees grow "some really strange leaf configurations," possibly indicating the possible introgression (the entry or introduction of a gene from one gene complex into another) of gambel oak and post oak. "If gambel oak becomes stronger than bur oak, the leaf shape and other characteristics will change," he said. He added that leaf shapes on trees in Bur Oak Canyon generally follow post oak characteristics, which include rough-feeling leaves with stellate hairs.
The fringe on the acorn caps within Bur Oak Canyon shows lots of variation, Buchanan said, an indicator that species other than just bur oak are definitely involved.
Although bur oak itself is highly variable, variations in twig color, bud size and color, bark texture, flower color, acorn cap, growth habits in Bur Oak Canyon are indicators of less than a pure bur oak population, Buchanan said. "The canyon is predominately bur oak, but not pure bur oak."
He continued, "In an isolated sub-population (such as Bur Oak Canyon), we would expect more uniformity. But Bur Oak Canyon is just the opposite. This new information is exciting ... a new radical idea."
The next level of study of Bur Oak Canyon may be on the genetic and molecular levels, Buchanan said. A molecular biologist would study Bur Oak Canyon samples and compare them with the closest range that would most likely have contributed to this canyon, he said.
Unfortunately, there isn't a lot of tree regeneration of any particular oak species in Bur Oak Canyon, probably due to cattle grazing. "Cattle are hard on seedling trees," Buchanan said. "There are only a handful of seedlings in the two-mile canyon."
In Bur Oak Canyon, there is also a lack of squirrels, who carry acorns away to bury them somewhere other than where they fall, in the shade and in huge numbers, directly under the trees.
It is important to let the trees regenerate for the canyon's growth and continued survival into the future, Buchanan said.
Other speakers at the symposium were:
* Jack Phillips of Omaha, consulting arborist, who led a tree anatomy lab. "The most important thing for a tree's root development is air in the soil. Loss of air in the soil, due largely to compaction, is why trees die," Phillips said.
"Roots don't absorb anything," Phillips said. "They actively take things. It's not like a sponge. There's nothing passive about this -- there are no passive processes in a tree."
* Guy Sternberg of Petersburg, Ill., landscape architect, arborist, tree consultant, writer and photographer: The leaf galls that grow on bur oaks are harmless to the trees, Sternberg said. "They may look like a huge case of warts," he said, "but the tree will grow out of it, or grow with it."
Sternberg does not recommend spraying bur oaks for insects and foliage feeders. "It's worth it -- sacrifice a few leaves for a butterfly," he said. "Don't get out the 'kills all' and kill everything. The treatment is worse than the problem."
* Nancy Carlson of Genoa, anthropologist, archaeologist: Artifacts from any Indian hunter-gatherers, hunter-horticulturalists and semi-sedentary hunters from 12,000 years before present on could be found in Bur Oak Canyon, Carlson said.
Although Bur Oak Canyon would have been an attractive resource patch -- of deer, small game, vegetable foods and possibly knappable stone -- for Indians, she said, there is no archaeological evidence that historic tribes of Pawnee, Sioux, Apache and Cheyenne in Southwest Nebraska utilized acorns for food.
Carlson said it is not likely that Indians planted the trees in Bur Oak Canyon, but that the tree stand is a relict from many, many years ago.
* Justin Evertson of Waverly, assistant director for community programs of the Nebraska Statewide Arboretum: Oaks are some of the better-adapted trees for planting on the High Plains, Evertson said, as they are long-lived, tolerant of climatic extremes, adaptable to a wide range of soil types and resistant to most insects and diseases.
Oaks are not tolerant, he said, of many sprays and chemicals put on lawns, and strongly cautioned against their use around oak trees.
* Jim Goeke of North Platte, hydro-geologist with the University of Nebraska-Lincoln who explained how the geology and hydrology of Southwest Nebraska lends itself to the creation and growth of one of the oldest native stands of oaks in the Great Plains. Goeke examined the formation of canyon lands, the role of caliches (a soft, powdery limestone consisting chiefly of fossil shells) and natural springs in the Bur Oak Canyon ecosystem.
* Representatives of the "ReTree Nebraska" Initiative, a 10-year cooperative initiative to raise public awareness of the value of trees, reverse the decline of Nebraska's tree and forest resources and improve the health and sustainability of trees and forests. The primary goal of ReTree Nebraska is to work in partnership with people across Nebraska to foster the proper planting and maintenance of 1 million new trees by 2017.
Owned by the Roger Lewis family, Bur Oak Canyon is private property. Permission should be obtained before entering.
Hoffman said he greatly appreciates the graciousness and generosity of the Lewis family in allowing symposium participants to come out to the canyon.