Monday, February 19, 2018

Black Locust Inventory

A list of numbers rarely tells a compelling story.

Professional foresters use sampling techniques to estimate the age and species composition of forests.

My "forest" is small enough that I can take a census.  Accurate measurement is the first step toward being able to manage anything.

Accurate is a relative term.  You don't use a micrometer to measure a pile of manure.  You don't use a yardstick to measure turbine blades. I used a cloth measuring tape to measure the circumference of the trees at approximately chest height.  I rounded down to the nearest inch and tried to not measure anything less than three inches in diameter.

Circumference of stem on horizontal axis broken into "cohorts" binned by 5" increments.  Blue line is the number of stems in each cohort.  The red line is an estimate of the cubic feet of wood in each cohort. 

Based on these measurements, the greatest amount of wood, by volume, is in the first flush of suckers that arose around the mother trees.  The volume was crudely estimated by multiplying the cross-section at 48" by twenty feet.  Twenty feet was chosen as that is the height where most of the stems bushed-out.  Clearly,  more wood could be collected from the larger trees if more effort were expended.

The largest number of stems is in the smallest circumference recorded which is not surprising.  Then there is a large step down and then fairly linear decrease in each cohort.  The reason that there is a large step down at the start is that the 3.5"-to-5" diameter is ideal for posts and suitable for burning without splitting.

Black Locust (Robinia pseudoacacia) posts make outstanding fence posts due to the rot resistance of the heartwood.  The tree also fixes nitrogen and the flowers are a prime nectar source for bees.  Other than that, the tree is weedy---it suckers, thrives in poor soils, is thorny and is difficult to eradicate--- and usually displays poor "form".  I consider Black Locust to be one of my social peers.

Factoid of the day
The heartwood of Black Locust fluoresces under ultraviolet light.

And here is a short monograph on Black Locust lumber and its properties.

1 comment:

  1. The house that my folks bought out in the country far from town, on top of a ridge in upstate NY, had begun life as a log cabin back in 1802. It had been expanded upon over the years. But expanded to the east, as to the west sat a very large black locust. It was obviously the granddad to all the others on the front lawn. There were about 40 in all. But the tree that grew right outside the front stoop was about 8 feet took 3 adults with arms outstretched to reach around it. Over the 56 years my folks owned the house, it just got bigger.
    Dad would occasionally cut one down that was interfering with another tree, then cut it up into posts for the garden, and some firewood.
    In June when you walked out the door, all you could smell was the locust flowers, and all you could hear was the bees buzzing away. They loved the locust nectar, and we loved the honey that came from it.
    The only thing I hated about those trees was in the spring it was my job to pick up all the sticks that had fallen over the winter, so the lawn could be mowed. Many of those sticks had industrial sized thorns and stickers on them. And there were at least a million of them! :)


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