Nature Notes

A Venerable Oak Tree

By Dan Miller

Behind the Arboretum’s Andrus Learning Center stands an impressive Bur oak (Quercus macrocarpa).  It is a well shaped tree approximately 60 feet tall and with a canopy spread of nearly 90 feet.   Although there are other oak trees at the Arboretum that are both taller and with wider canopies, as far as we know this oak has the distinction of having the trunk with the widest diameter.  Arborist and foresters use the measurement ‘diameter at breast height’ (d.b.h.) to indicate trunk width.  This oak tree has a 52” d.b.h. which is equivalent to a circumference of 14 feet.  To determine the age of this tree, there is a technique by the International Society of Arboriculture where the age can be estimated by multiplying the d.b.h. of the tree by a species specific growth factor.  For bur oak we can use the white oak growth factor of 5.0 which would give us an estimated age of 260 (52 X 5).  But according to Dr. Gary Johnson from the University of Minnesota Department of Forest Resources it is necessary to make an adjustment to the age based on the quality of the growing site.  A tree on an unfavorable site may be older than the formula age and conversely a tree on a favorable site may be younger.  The site behind the Learning Center offers a moist, well-drained soil which is favorable for bur oak growth; therefore an adjusted estimation would put our bur oak at 225 years old.

Two hundred and twenty-five years ago our oak tree began its life.  Most likely it began when an acorn from a nearby tree serendipitously nestled into a bare spot in the vegetative ground cover.  Foraging birds and mammals such as woodpeckers, jays, mice, squirrels, deer or bears did not discover the acorn and with suitable temperature and moisture conditions, it germinated.  It was the early 1780’s.  At that time, most of the land area that comprises the Arboretum was wooded and part of a large, forested native plant community that was designated by the early French explorers as the bois grand.  Later English-speaking inhabitants translated it to the “Big Woods”.   This forest covered more than 2,000 square miles of south-central Minnesota and extended in a band 40 miles wide from Mankato to Monticello.  The Big Woods plant community is comprised of elm, sugar maple, basswood, and oak in the overstory layer.  Ironwood, bitternut hickory, prickly gooseberry, red-berried elder, and chokecherry are common species that can be found in the subcanopy and shrub layers. Our bur oak seedling penetrated its roots deeply into the soil and established itself among other tree seedlings and shrubs in the late 1700’s.  This well-drained site between two wetlands offered an ideal environment for prosperous tree growth and development.

At the turn of the century, the forested area south of Lake Minnewashta was an uninhabited wilderness.  The indigenous people of the region were the Mdewakanton band of the Dakota Sioux but their villages were located along the banks of the Lower Minnesota River near Shakopee.  From their home sites, they would travel north out of the river valley on hunting, fishing, and gathering trips.  Presumably they would occasionally visit the area that is now the Arboretum and would have passed by our bur oak sapling that by now may have been 15 to 20 feet high.

The vast area of the Upper Mississippi River Valley at this time was sparsely populated with fur traders and Indians and was French territory.  It did not become part of the United States until 1803 when the French sold it to us as part of the Louisiana Purchase. To open up the territory to American development, the government took possession by establishing a fort at the junction of the Mississippi and Minnesota Rivers.  Fort Snelling was completed in 1825 and thereby allowed an influx of settlers who came to the new territory looking for opportunities to acquire land and to set up farms.

The first settlers reached the areas south of Lake Minnewashta around the mid-century point and began to clear the trees from the land to grow crops on the fertile forest soils.  Several early pioneers homesteaded the lands of the present day Arboretum.  The early history of one of these pioneers is chronicled in the book “A Frontier Family in Minnesota: Letters of Theodore and Sophie Bost, 1851-1920”.  Pioneers like Theodore Bost worked arduously to create farm land.  They had to clear the “Big Woods” trees first.  They cut the oaks, maples, and basswoods and used the high-quality lumber to build their homes and barns or burned it as firewood to heat their homes.  They grew corn, wheat, oats, forage crops, fruit trees, potatoes, rutabagas and many other vegetables on the cleared land.  They raised oxen for work animals, horses for transportation, and dairy and beef cattle for food. Many of their parcels were 160 acres so several homesteads at this time could be found on the lands of the present Arboretum. The Bost farm was located where the Arboretum’s red barn currently stands.

According to the plat books at the Carver County Courthouse, the first person to homestead the land of our bur oak was Joseph Aldritt in 1856.  At this time he may have noticed our oak tree which would by now be approximately 16” in diameter and would have begun developing a distinct gnarled bur oak shape.   The original Aldritt homestead changed possession several times in the next 15 years.  Joseph Aldritt sold the parcel to Uriah Thomas in 1858, who sold it to Ralph Kirkham in 1861, who in turn sold it to Ferdinand Kroening in 1871.  Possibly these early pioneers allowed their livestock to browse the understory  nearby our oak, reducing the competition and allowing our tree to produce an open-grown canopy; or maybe one of these families that lived in the house on the hill to the north cleared other trees around the oak to give our tree an advantage.  Nevertheless, our oak tree thrived under these conditions.  It grew massive limbs and developed a wide canopy.  It was spared from fatally damaging wind storms and was not hampered by injurious diseases or insects.  By 1958 our bur oak was a prominent feature in the overstory, among equally majestic white oak neighbors.  It was at this time the land was finally purchased by the University of Minnesota to build a landscape arboretum.  The original house on the hill was gone then and a barn stood where the Learning Center is today.  The barn was eventually torn down and the Learning Center was constructed in its place in 1983.  Today this tree can be found behind the Learning Center where it towers over a naturalistic playground for kids and nearby teaching gardens.  It maintains its intrinsic beauty, its superior form, and more importantly it’s good health so perhaps if will survive for another 100 years or more.


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