Installing already vigorously growing tree produced in Nursery, and sold between ages of 6-14 is best for success. Compared to planting a sapling which can disapointingly fizzle. But on other hand its super important that a replacement be germinated from ancient locally evolved seed, from tree which had already proven can survive 100+ years. Otherwise your wild forest that exists now, will be long forgotten once last of old growth trees disappear. How many new Oaks or Pecans have grown on property over last 50 years? Unfortunately natural conditions that once produced your groves "youngest" old wild trees, no longer existed since then. Like prairie fire, and other still unknowns. Such as certain plants and wildlife conducive to survival of Oak past age 40. Another possibility is, that your whole grove of trees once grew up alongside each other without shading each other out. On the other hand...If replacing an old human planted tree, like English Oak. Then replanting with another native may not be so important.
I suggest continuing to grow saplings from local acorn on other portions of your property, since like someone else said. Young trees in forest spend years producing root system while waiting to bolt once opportunity arises. Sugar Maple seedlings do this, by completely take over forest floor, letting nothing else grow. So you might want to check into seedless cultivars, like Cappuccino version of Kentucky coffee tree. Another option from others as well, was to plant species known to tolerate spots conditions. I suggest researching classification of your local ecosystem, which lists all species that evolved alongside each other. And commonly named after most important and most influential species of an individual ecosystem type. Which are many times named after trees, such as Oak-Hickory or Sugar Maple-Basswood-White Ash. This list will detail understory species and tree species that regrow naturally alongside Oaks & Southern Illinois evolved Pecans. And would be great addition to your collection. What other local old growth tree species continue to grow in your area? Black Cherry, other Hickory types? I like Shagbark! Did you know America loosing all her Butternut Hickories? Only sick trees are last survivors, and its now become easy way to identify hickory type tree sadly.
Know that any new planting will require structural pruning over its first 20 years. Nurseries do this pruning to retain strong "Apical dominants" until selling trees. Your new Oak would require this, by maintaining one main trunk, lifting off like a firework skyward. Then exploding its widening crown high up in open canopy. Your existing Oaks will give you idea how high up main trunk should be, before allowing it to diverge into several trunks. Resembling a spruce tree with one main stem and all slower growing "Laterals" giving girth to trunk. Red Oaks and Sycamores have strong apical dominance. And avoid a "Wolf" structured tree, which produces many main trunks and main crown low to ground. Like firework going off prematurely. I suggest these details I had learned from past observations, anytime a community tried to "Replace" an old historic tree using its seeds. Not knowing it required special pruning during formative years. Thus turning into a bush and requiring removal before age 50. That's what happened to every Bicentennial Oak planted in 1976, quickly disappearing today.
Settlers had no success replanting wild Oaks belonging to long lived White Oak family. Because of long taproot being severed while transplanting. Planting seed assures tree "Root crown" grows level with grade. And while nurseries think they have cured problem of transplanting from White Oak family over only last two decades. 99% problem of any Nursery tree regardless of species, arriving with Root flares already too deep in rootball. Requiring planter to first perform "Root flare excavation" to find what level tree originally born at. Caused by past sapling being uppoted deeper and deeper each time in nursery. Plus when dug out of field, wrapping burlap causes dirt from sides to be dumped on top of trunk. Suggest selecting tree with good structure and visible root flare back at nursery, and remember no new soil gets applied over existing root ball! (New discovery! Projenitor of worlds ancient White Oak genus, evolved on pre historic East coast, and spread to Eurasia. U.S. Experts say...Take that China!)
kthayes...everyone thought for trees natural structure...it was totally up to new tree to take care of itself up until at least age of 20 before requiring professional pruning. I hope knowing even more now, you will now see replacement as bigger challenge. Becoming a learning experience that will continue to teach future generations through your trees continued survival. Revealing secret, that everything tree will become...is based on human relationship forged with organism over its first 20 years. You have already begun by asking the right questions! Enjoy!
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The conical vine tree
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