Black locust trees are abundant where I live, and I have some questions about them.
Why does the same tree sometimes have big thorns on one branch, small thorns on another branch, and no thorns on yet another branch?
I have heard that fence posts made of locust will take root. Is that true?
Bump.
The production of thorns may be related to the risk of damage from grazing animals - the true acacias (which are related to the false acacia) do this - they produce wickedly thorny growth around the edge of the canopy, but the inner crown - out of reach - is comparatively thornless.
Thorns cost the plant energy to produce, so it makes sense to deploy them only where required.
I’m not sure if it does this as a response to being eaten, or if it’s just an innate pattern - if the former, then it’s entirely possible for other patterns of thorn distribution to occur - and in response to other stimuli, such as perhaps branches being brushed by people walking past on a path.
Locust trees have a very aggressive rooting habit, ranging far beyond the drip line. It wouldn’t surprise me to see a locust log taking root and becoming a new tree.
Thornless locust trees are available, and if you get a male one, it will be seedless, too. It’s a trade-off, for the male makes a lot of sneezy pollen.
I took a large female locust out of my back yard 3 or 4 years ago. It had produced 24 waist-high bags full of locust pods in its last year. Even though I burned out the stump for 3 days, I’m still getting little locust sprouts from the old roots.
Slightly off-topic, but you might want to consider that stand of locust as being useful for things other than fenceposts. While Black Locust was historically the wood of choice for Trunnels (pegs) to hold sailing ships together, it has only fairly recently been documented why the old farts chose it: In all measures of toughness, strength, and rot resistance it is equal or better than the specie known as “live oak” or “swamp white oak”, which was otherwise the toughest thing native to the U.S. If your stand of trees is free of the locust borer beetle, boat builders will beat a track to your door for the stuff. Any limbs you cut off are the best firewood around: as much heat as any hardwood but no sparking or popping.
Our locusts tend to be short-lived and structurally unsound, so I suspect they may have the beetle, but we do have a couple of really big ones that have held up for a long time. Thanks for the advice, anyway!
Seeds from thornless locust trees do revert back to ones with thorns, so if you have a seedless you still can end up with thorny trees all over. They still have the aggressive sprouting from the roots too.