Thursday, January 7, 2016

Oak Savannas

Oak savannas are ecosystems that depend on fire for their continued good health.  In the time before settlement by people of European descent, it is suspected that Native Americans set fires to improve hunting, foraging and agriculture, much like people in developing countries use fire in slash-and-burn agriculture.

 Development: the plow, the bulldozer, the sprayer and modern man's insistence of fire suppression wreaked havoc on those ecosystems.  For the most part, they exist as small fragments and latent seed banks.
Your secretary has requested me to describe the appearance of a Michigan oak openings in its
primeval beauty. Such a description would require the eye of an artist and the pen of a poet.
Much as I loved those forest scenes, I have not words sufficient to give you an adequate picture of them...(countless species of wildflowers) all these came on together in rapid succession, comingling in the wildest profusion, and stretching as far as the eye could reach under the delicate oak foliage. Why try to describe the earlier growth of violets, asters and all their sisters, their cousins, and their aunts. The now nearly exterminated fringed gentian [Gentiana crinita] then flourished in abundance... I see the day coming when there will not be a patch of forest where the child may see the flowers which charmed his parents’ eyes. Like buffalo, the deer, the wild pigeon, the Whip-poor-will and the prairie hen, these, too, will soon be things of the past. The last pioneer will soon be gone and with him many of the native plants and animals will soon disappear (Hoppin 1893).

Even in the best of times, Eaton County had little Oak Savanna.  But  look at the "7" shaped green line starting in the southeast corner of Eaton County and then bending south shortly after entering Ingham County. Based on botanical evidence, the west end of that "7" is near the corner of Haven-and-Grove street in Eaton Rapids city limits.  The top bar of the "7" follows Plains Road east to Gale Road, and then to the town of Onondaga.  A hat-tip to Bill Botti for pointing out the obvious reason for the reason behind the names for  Plains Road and Grove Street.

Eaton Rapids School Complex is on the south side of Plains road.  That is, the historic ecosystem for that location is Oak Savanna.  AND, they have some under-utilized property in the southeast corner that would be a dandy place to reclaim.

Doing my homework

One of my reasons for sorting through my "Red" oak identification is that I wanted to find some local sources of Black Oak (Quercus velutina).
Black Oak on left.  Northern Red Oak on right.  Identification by leaves is screwy because leaf form changes significantly based on juvenility of the tree, rate of growth and how much sun the branch was receiving.

After looking at a few hundred Black Oak, I must disclose that Black Oak is not my favorite species of oak.

It may be that they are so closely tied to the fire ecology.  The trunks of Black Oaks look like they were rolled out of Play-doh by five year old boys.  They are lumpy!  Most likely, fire caused them to die back.  They pushed multiple stems from the root collar and it took a while for one of them to become dominant.
This is one of the prettier ones.

And then there is the matter of mast production.  Northern Red Oak produces between 200% and 400% more pounds of acorns per acre than Black Oak.  And the acorns are bigger.  What is not to like about Northern Red Oak?

Local Black Oak acorns on the left.  Local Northern Red Oak acorns on the right.
I think the only reason that Black Oak outcompetes Northern Red Oak in the fire ecology is that it is more aggressive in sprouting from the stump and because it produces more acorns (by count) and seedlings don't need as large of an endowment to grow out of the ash while the larger NRO acorns have an advantage if they fall into tall grass.

Burr Oak

Furthermore, I must disclose that I am very fond of Burr Oak.

These acorns were removed from the ERJ seed vaults.  They are dark because the are stratifying.  The cups on this strain of  Burr Oak adhere.  The cups function like little personal floatation devices, allowing the acorns to float down the floodwaters and colonize new flood plains.  This little PFD is also seen on Q. lyrata, suggesting that Q. lyrata genes infiltrated the Q. macrocarpa species some time in the past.  This seed strain is known as "Idaho Sweet Burr Oak".  Since Burr Oak are not native to Idaho, one must assume that travelers on the Oregon trail brought more than daylily bulbs and lilac bushes.

Burr Oak is the sawed-off shotgun of the White Oak family.  If you planted 1000 Burr Oak acorns you would see an incredible range (scatter) of phenotypes.  You would see fast growing types and slow growing types.  You would see smooth twigs and corky twigs.  You would see non-incised leaves and deeply incised leaves.  You would see abscissing and non-abscissing cups.

The individual Burr Oak saplings that exhibit "Corky Twig" are inherently more fire resistant than individuals that do not exhibit corky twig.  This twig had a wooden core of 7mm and the widest tip-to-tip of 26mm.  This twig was cut from a sapling near the corners of Hammond and Cross in Jackson County.
Suppose that the selection pressure exerted by frequent fires ceased for two or three generations.  Individuals that did not invest resources in corky twig would outgrow its more prudent neighbors.  The population would shift toward less corky twig.

Suppose one were to plant acorns to regenerate Oak Savannas, one would be well advised to select acorns from legacy trees that predate settlement by people of European descent.  That would be one way to ensure that one's seedstock had not undergone genetic shift. 

One way to estimate a tree's age is to multiply the diameter by some factor.  For example, in Missouri, they suggest that one take the diameter of a White Oak and multiply the diameter in inches by five to estimate the tree's age.

Michigan is farther north than Missouri.  Our growing season is shorter.  Trees grow more slowly.  A multiplier between 6 and 7 might be a good number for Burr Oaks in Michigan.  If one assumes that settlement started in earnest in 1830 (statehood was granted in 1837) then Burr Oak trees with a diameter in excess of 30" are likely to have germinated before settlement.

Choosing even older trees has other advantages.  They survived more test winters, more fires, more diseases and insect infestations.

It is even better if one can find a grove of these trees.  That increases the chances that both parents are uber-survivors.  Here are pictures of three Burr oak that are growing within 200 yards of each other near the corner of Hammond and Cross roads in Jackson County, Michigan.

East tree.  Fifty inches diameter at chest height.
Middle tree.  Fifty-five inches diameter at chest height.  Canopy is approximately 115 feet in diameter.  One tree of this size per acre would result in a perfect 25% canopy cover.
West tree.  Fifty-three inches diameter at chest height.  All three of these trees are probably over 300 years old.  These trees do not look "big" because they are so well proportioned.  You cannot appreciate their size until you walk up to them.
Saplings near these brutes are very heavily "corky twigged".  That is where the "corky twig" photos came from.

Not the best picture.  This is a furrow in the bark of the middle tree.  It is over 4 inches deep, bottom to crest.  That is thick bark.
The three brutes are not the largest Burr Oaks.  Both the McBain oak in Missouri and the National Champion tree in Kentucky have a diameter of approximately 90 inches.

Acorns from the "three brutes of Jackson county" would be awesome seeds for regenerating Oak Savanna in Eaton Rapids.

1 comment:

  1. I too, have a special fondness for bur oak.
    First became acquainted with them while living in mid-Missouri - was initially amazed at the size of the acorns and the ornate caps - and by how favored they were by the deer.
    Began collecting acorns and seedlings from across the species' range... acorns ranging in size from 100/lb to 6-8/lb... and wide variation in leaf morphology and corkiness of stems, as you've already described.
    On visits home to Alabama to visit family, I found that I'd been surrounded by them for most of my life... Q.macrocarpa is only native to a tiny little isolated spot in Montgomery County, AL, but Auburn University had planted them extensively around the campus as 'street trees'... and the majority of trees on the veterinary campus were large-acorn strain bur oaks... I'd just not noticed them during the 10 yrs I'd studied and worked there.
    Q.macrocarpa is quite common up in the central 'Bluegrass' area of KY... but not very common over here in the hinterlands of western KY. Very worthy of consideration though - both as a residential landscape specimen, and as a wildlife mast source; tough, tolerant of a wide range of soil type/pH/moisture, fast-growing in youth, and early to begin bearing low-tannin acorns - relished by wildlife, and holding significant potential as a human foodsource, as well.


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