Giant fruits the size of softballs litter the woods near trail post #1. It’s a ridiculously over-the-top spread, laid out for dinner guests that won’t be coming. Squirrels and deer work on the freeze-softened remains but they can hardly make a dent – this fare was intended for something much bigger.
They’re called “anachronistic fruits”; after falling from the tree these oddly large seeds or fruits tend to lay around in heaps, mostly unconsumed. Often defended with an armory of thorns – ridiculously wicked against our puny modern fauna. They’ve lost their eaters, the theory goes, and hence their dispersers as well. The story of how this theory was developed is itself interesting: http://www.americanforests.org/magazine/article/trees-that-miss-the-mammoths/
Though it’s been only 11,000 years, we don’t know exactly who the eaters were. But it’s a safe guess they were able to reach as high as the horse-like species from Asia in the pic below (created by amazing illustrator Roman Yevseyev). Which explains a lot about the evolution of Osage Orange, the tree with with the giant fruits.
Giant Ground Sloths were likely eaters of Osage Oranges, though others surely joined in, since in North America there were “five species of deer or moose, two llamas, a camel, three horses, four ground-sloths ranging from 400 pounds to 3 tons, a 600-pound armadillo, a 2,000-pound turtle-like glyptodont, two ox-like species, a 5-ton mastodon, a 6-ton woolly mammoth, and a 9-ton Columbian mammoth” – all of which became extinct at the end of the Pleistocene.
There’s a great book on the subject: “Ghosts of Evolution” by Connie Barlow. http://thegreatstory.org/ForestCanopies.html
But this post isn’t about them exactly, but more about the process of natural selection. Osage Orange’s extreme adaptations bear witness to the co-evolution of eaters and the eaten. At once inviting and repelling, it’s unripe fruits are protected by painful thorns and contain a glue-like milky latex that likely makes them indigestible. (Try cutting a green one open sometime, your fingers will be sticky all day!) Very young trees have especially healthy thorns (I know this from painful experience) since they’re most at risk from browsers. Even the form of the tree is odd – mature ones have a massive trunk with low and widely arching branches, but still tantalizingly out of reach for big animals. In form it’s a tree of open country, like the Acacia of African savannas. Osage Orange is part of the Moraceae, or Mulberry family; the fruits actually resemble huge green mulberries more than anything else.
It’s reasonable to expect this tree would either go extinct, or that it would adapt to smaller dispersers. But it takes a while for a tree to forget, genetically speaking. The last megafauna disappeared about 10,000 years ago – only 50 generations for a tree that can live 200+ years. It would take a lot longer for significant adaptations to emerge. No surprise, Osage’s range had shrunk considerably at the time of the first European descriptions; it only occupied the Red River drainage in a small part of Texas and two other states.
Despite what some articles claim, the fruits are eaten by a few present-day animals. Or rather, the fruits are picked apart and the seeds are eaten, mostly by squirrels. I have seen deer occasionally eating the freeze-softened pulp but it’s not a preferred food. Horses and cattle are slightly better substitutes, and have helped spread “Horse Apple” fruits around.
But in a quirk of fate, Osage Orange found a better substitute disperser than any of these. The very adaptations that helped the tree survive ancient herbivores, made it desirable to humans as well.
With bend-but-not-break flexibility to withstand the assaults of giant sloths, Osage became one of the finest bow woods of North America’s first people. The tree was widely planted and traded. Much later, hedge rows like tangles of living barbed wire were used to fence in livestock. Osage hedges were”horse high, bull strong and pig tight.” (Jonathan Turner, 1847) This practice (ended by the widespread use of true barbed in the late 1800’s), likely explains the presence of the trees in our forest.
A last line of former Osage Orange hedgerow lines the hilly stretch of Trevillian Way bordering Creason Park. They still produce giant fruits, which are a true hazard of driving the road in fall – one bounced off the hood of my car. It’s about half a mile from the concentration of old trees in the SW corner of Beargrass Creek SNP. The trees were probably once scattered across the land that is now the preserve and the park, back when it much of it was pasture for horses and cows. Due to their thorniness, the young trees are among the few that can thrive in heavily grazed areas.
There are two other thorny native trees, both in the Pea family, that tend to spring up in old pastures; Black Locust Robinia pseudoacacia and Honey locust Gleditsia triacanthos. The latter species is also a possible anachronism, though the case is not as clear. As deer hunters well know, the long sweet pods of honey locust are a big draw for White-tails. Many other species consume them too, and they continue to be well dispersed. A giant Honey Locust stands just behind the arched branch of an Osage Orange in the pic above. I’ve seen them in such proximity in several places, perhaps their joint defenses helped shelter them as young trees. The case for anachronism rests on the massive thorns that festoon the Honey Locust’s trunk, and the fact their seeds need strong “scarification” (like the grinding of big teeth) to germinate.
But what about the mostly inedible Osage Orange – will it eventually disappear? I don’t believe so. In our little “novel ecosystem” in particular, human curiosity ensures dispersal for its fruits. When I used to teach school groups the kids would beg to pick them up. If nothing else, they will always benefit from children’s need to throw things. Osage will abide.