Tree of the Week for Sept. 23rd-Sept. 30th, 2007: Gleditsia triacanthos
Whelp, despite my perfectly legitimate excuse for not having posted a Tree-of-the-Week so far this week, it's now time to get down to business and start typing up this week's most wonderous Tree. So, without any further ado, let's kick out the jams, motherfuckers!
These late September days we are currently travelling through are, surprisingly enough, a wonderful time to be a tree-fancier in a big city like Chicago, and that fact is largely the work of this week's tree, Gleditsia triacanthos, the Honey Locust. I have heard this tree's aesthetic called an 'Impressionistic' one, and I cannot deny that this is a perceptive opinion. The Locust's long, feathery leaves, its flattened, squarish, acacia-like crown, and the dappled, shifting light that it lets through to the ground all combine to give one the feeling that one is observing something which better belongs in a painting by, say, Cezanne. But at this time of year, the effect is heightened, for in these early days of Autumn the tree's leaves slowly begins to change from its customary light green into an equally light and airy gold. Passing by them on the street, one falls under the impression that the tree is constantly being struck in suitably dramatic fashion by isolated shimmering sunbeams streaming down from between dense, gray clouds. But no - the Honey Locust requires no star to highlight its beauty, but rather does so by means of its own ingenious internal chemical factories.
Now, those of you who know me well have already heard a great deal about this tree, for it is both one of the trees that I most heartily love and one of the members of our North American sylva which is the most eminently visible to a grime encrusted city-slicker. This second fact is due to its immense popularity as a street tree throughout all of our great nation's major metropolitan areas. In Chicago, it is the single most frequently planted tree along streets both residential and commercial, and I do believe that it can lay claim to that same accomplishment in both New York and Los Angeles. "If you can make it here," they say about New York, "you can make it anywhere." And so G. triacanthos has, not only thriving in the harshest of urban environments, but also being planted in such divers locales as Europe and Australia - in both of which places it has been so successful as to become a major invasive 'weed' species. In Australia, in fact, it has been given the deliriously exciting common name of "McConnel's Curse". Or, at least, so claims Wikipedia.
Why is this tree so incredibly successful as a street tree? Why has it been planted so ubiquitously throughout our nation's major cities? The answer lies in a host of adaptations that the tree has which make it a near-perfect urban survivor. From the perspective of a human forester, one of the tree's chiefest advantages is its rapid growth rate. It might not grow as fast as a cottonwood, but during the first ten years of its life it can spring up at the more than respectable rate of two feet a year, meaning that one can have grown a truly respectable shade tree from a seed in well under two decades - meaning that one does not have to look into the vastly far future when planning neighborhoods around this tree. Furthermore, it is among the most salt-tolerant of trees. In the middle of winter, when tons of salt are poured out on the streets of our cities to prevent the excssive formation of ice slicks, the ability to survive the leaching of all this salt into the soil without being poisoned or losing literally tons of water is very important to a tree, and G. triacanthos can survive even on the edges of freeways which are even more salt-encrusted than a city's residential streets. I should note, though, for the sake of intellectual integrity, that while almost all the sources I have looked at agree on this property of the Honey Locust's, the USDA does not, and I normally treat the Department of Agriculture as among my more unimpeachable of sources. Due, however, to the unanimity, and even enthusiasm, with which my other sources treat this fact (and I include such reliable people as the National Arbor Day Foundation among these sources), I have decided to, for once, disbelieve the USDA. Especially since G. triacanthos so patently does flourish alongside the busiest of downtown streets, and this is a property one would expect of such a tree.
But wait - there's more! The Honey Locust is also tolerant of a wide range of soil pHs. It might not be as acid-loving as, say, rhododendrons or pines, but it is still tolerant of rather acidic soils, and can also survive well in soils that are rather more alkaline than many plants would prefer. Given the odd fluctuations in general soil chemistry likely to be found in an urban area, with all the pollution of a million car exhausts, a thousand factories, and an infinity of sewage pipes settling into the ground, such an insouciant ability to withstand these constantly changing, and generally unpleasant, conditions gives the tree another advantage. Furthermore, G. triacanthos is also able to survive a wide range of temperatures, minding neither the swelteringest hundred-degree days of summer nor the bitterest minus-twenties of the coldest winter. Those of you who, like me, live in Chicago can easily appreciate how essential both of these capabilities are, but you may not fully understand that trees are, like their animal counterparts, very susceptible to their environment's ambient temperature. Birches, for example, will wither and die if exposed for too long to the direct rays of the summer sun, whereas a live oak will quickly give up the ghost if a frost lasts for more than just a few days. But the Honey Locust shrugs off both of these extremes with equal ease. Also shrugged off with ease by this hardy tree are all but the most terrible droughts. Though it prefers a nice, deep, moist soil, and is, in nature, most frequently found in moist but well-drained river valleys, it seems to be unfazed by extended dry spells.
Gleditsia triacanthos is among the easiest of trees to identify, loudly proclaiming itself as 'unique' compared to all other common American trees in a variety of ways. I have already mentioned its fern-like leaves, either singly or else doubly pinnately compound, each seven or eight inches in length, and whose small, oval, spoon-shaped leaflets are all about a half-inch in length. This last fact provides a convenient way of distinguishing between it and the similar leaves of the Water Locust (Gleditsia aquatica) and the Black Locust (Robinia pseudoacacia), both of whose leaflets are much larger, a full inch or two in length. Also very characteristic is the tree's bark, which has a wonderful iron-gray color, and forms large plates along the trunk that are distinctive. The Honey Locust has a spidery growth habit, too, that allows one to identify it even at a distance. The tree rarely grows straight, producing a solid vertical trunk reaching high up into the air, but instead wriggles and twists as it grows, forming a main trunk that seems rather crooked and which soons sprouts out into many large diverging and forking branches. I am told that, in the rich lowland soils which it most delights in, the Honey Locust can reach heights of well over a hundred feet, but I am somewhat skeptical of this claim. Certainly, though, G. triacanthos is a goodly-sized tree, able to grow a solid seventy or so feet without even breaking a sweat. It also can produce a very wide-spreading crown, whose diameter at maturity can be just as great as the tree's height - a full 70'. Its flowers, which are rather small and inconspicuous, are nevertheless a pleasing creamy white or green in color, and appear in late spring, in May and June, and apparently have a reasonably strong and agreeable odor. I confess that I do not recall having ever gone up to smell a Honey Locust's flowers, and so cannot report back to you if this tale is correct, but next spring I will most certainly do so, and would also encourage all of you out there in TV-Land to do the same. Supposedly bees like this flower's scent as well as people, and seek it out, though it is not known as a great honey-producer or flavorer.
The two most distinctive traits of this tree, though, are its fruit and its thorns. Its fruit is a bean - and it is a true bean, for G. triacanthos is a member of the Fabaceae, the bean family which is so mighty and predominates in all of this world's terrestrial ecosystems - that is usually about 8" in length, though they sometimes reach to almost two feet long. These fruits - some of the largest in the entire spectrum of North American trees - begin appearing in early September, and slowly twist themselves into a corkscrew shape before dropping off over the course of the winter, which means that a Honey Locust can, even after all its leaves have dropped, still be covered with twisting red-brown bean pods, each containing some dozen seeds a centimeter or so in length. These seeds are surrounded by a sweet-tasting edible pulp, from which the tree gets the "honey" in its common name. This pulp is well-loved by deer, cattle, and other large herbivores, and is, I am assured, completely edible to people, and was indeed used as food by this continent's autochthonic inhabitants, who also fermented it to make a beer. I have never tried to eat Honey Locust pulp, but I certainly do plan on it. I feel somewhat suspicious of the fruit on city-grown trees, for the Lord alone knows what sprays they've used on it and how much of the city's pollution has been absorbed by the tree and passed on to the fruit, but there are several large, handsome Honey Locusts in the yard of my parents' house out in Suburbanland, so the next time I'm there, by God! I'll try me some Locust flesh. As for the thorns, they are truly impressive. Each one can be up to five inches long, and they frequently come in dense clusters along the trunk. These thorns grow straight out of the woody trunk of the tree, making breaking them off a Herculean task. But not all Honey Locusts have thorns, and those that do have them in very different quantities. Some trees are covered with them, whereas others have but a few. The ones most commonly planted in urban areas are from thornless varieties and cultivars (i.e. G. triacanthos inermis, G. triacanthos 'Sunburst', etc.) but it is nevertheless not uncommon to find one with a full set of thorns popping out of its trunk to menace passers-by.
The Honey Locust is a storied tree, with a dramatic history stretching back into the distant past, into the long-vanished era before the everlasting ice of the North rolled over this continent and changed its face forever, before any human eye ever saw any of the continents of this hemisphere. Since those two most characteristic features of the tree - its fruits and its thorns - play a key rôle in this story, it seems fitting to tell that tale at this precise point in my exposition of G. triacanthos' virtues & vices. In that distant pre-glacial epoch, North America was still home to giant animals the likes of which are not to be seen to-day: Saber-toothed cats, mammoths & mastodons, giant beavers(!), cameloids & llamas, dire wolves, cat-faced bears, and, of course, Megatherium, the giant ground sloth, a huge, possibly omnivorous animal that stood twenty feet tall when standing on its hind legs and had claws as long as a human forearm on both its fore and hind limbs. Evolution being the most opportunistic of masters, it is not to be supposed that there were no trees whose phenotypes were adapted specifically to take advantage of these ancient 'Giants in the Earth', and it is now hypothesized by many scientists (excellently summarized by biologist/science popularizer Connie Barlow in her book The Ghosts of Evolution) that the Honey Locust was just such a tree. Consider, for example, its thorns. In these latter days, what purpose could they serve? Do they defend against deer? No, of course not; a deer's head is certainly nimble enough to avoid the dense clusters of thorns on the side of a tree; they are no deterrent against those ruminants. Furthermore, although a young G. triacanthos might have something to fear from deer browsing their leaves, an older example of the species, with most of its limbs well out of reach of the mouth of any cervid, scoffs at the notion of deer posing a threat to its livelihood - and yet will still produce those intimidating thorns. And in the fall, when buck deer so vigorously rub their antlers against tree bark to scrape off dead skin, in the process often mortally wounding the tree that they do this against, the Honey Locust is not at all the sort of plant that they take delight in. They prefer trees whose bark is slippery, like the Willow, not one whose bark is as steadfastly attached to the wood 'neath it as is that of the Locust. So what purpose have these brutal thorns? Obviously, to defend against those extinct titans, the mastodons and Megatheriums who must once have loved the taste of Locust leaves.
Its fruit is also curiously anachronistic in the modern world. It is clear that it co-evolved with some sort of animal to serve as its dispersion mechanism, for Evolution does not go to the trouble of sweetening a tree's fruit with sugary pulp unless that plant has something to gain by it. Furthermore, the seeds that lie waiting within these pods have a coat that is thick enough that the embryo within cannot get access to precious air and water unless the coat is first damaged in some way - say, by being eaten away by the powerful acids inside an animal's stomach. Indeed, it is by being submerged in sulfuric acid for ~1 hr. that G. triacanthos seeds are scarified for commercial propagation today. It is reasonably certain, too, that it must have been larger animals that the Locusts took particular advantage of, for to-day, although squirrels and deer will certainly take advantage of Honey Locust "honey", they do a poor job of seed dispersal, typically either avoiding or eating entirely the seeds contained within the pods. It is, in fact, the farmer's cow who does the best job of dispersing the Honey Locust's seeds, eating the pod whole for its sweet filling, and allowing the seeds to pass straight through its multiple stomachs, its powerful acids properly scarifying the seedcoat before it finally emerges from the cow in the middle of a nice pile of beautiful fertilizer.
So, we have an image of a Pleistocene North America where the Honey Locust co-existed with its predators, the giant herbivorous animals of the time, feeding them with one hand whilst keeping them at bay with the other. Given how successful it is in nature even in these latter days when it is bereft of any reliable dispersal mechanism, it must have been even more widespread in those ancient times. But, when the glaciers finally retreated, and the combined effects of climate change, diseases imported from the East, and the devastating efficiency of a new predator, Homo sapiens, combined to reduce our continent's megafauna to a fraction of what it once was, the Honey Locust must have retreated in its range, and rapidly. For G. triacanthos is not a long-lived tree, paying for its early vigor by expiring after little more than a century of life. So it must have retreated to areas where the deer and squirrels would still offer it their feeble services, though they be but pitiful handmaidens compared to its dashing servants of old, and to where fast rivers would carry away its pods and smash its seeds fearfully enough to break their pods before depositing them in rich loamy soil. But with the spread of sophisticated agriculture to the regions north of the Rio Grande, and the arrival of large Eurasian domestic herbivores (i.e. horses & cattle), the Honey Locust sprang back from its slow slide into oblivion. Spread first by those food and companions of Humanity, the Honey Locust has, in the past half-century, attracted the attentions of mankind itself, and its advantages have (as revealed above) allowed it to co-operate with humanity for the mutual benefit of both species, as G. triacanthos has now been reintroduced into vast regions where once it floundered, and spread to whole new areas where it was previously completely unknown.
Now, as might easily be imagined by the length of this essay, I am getting very tired of typing, and impatient for it to be finished. So I will gloss over the taxonomical relationships of this tree. But do not worry for your lack of information, for this tree is part of a truly mighty clan, the Fabaceae, and I will reveal to you more data about that impressive kingroup in many a later essay about its other arborescent North American scions. Let it suffice to say for now, that G. triacanthos is undoubtedly part of this family, second only to the daisies and orchids in terms of numbers of species, and that it is a member of the Caesalpinieae sub-family (which molecular studies have re-shuffled the membership of significantly, but which clearly includes both Gleditsia genus and the Gymnocladus genus, another prominent member of the North America's sylva). Let it further be said that, like most members of the bean family (for the Fabaceae is indeed the family that includes everything from lentils to peas to lima beans), G. triacanthos is an expert at obtaining nitrogen from its environment, both entering into even more complex relationships with mycorrhizas (root fungi) than do most trees, and also providing, amongst its roots, tiny nodules in which form a home for certain soil bacteria that exchange nitrogen that they 'fix' from atmospheric sources for sugar that the tree feeds them. This capability of beans makes them important players in ecological cycles worldwide, and G. triacanthos is thus, even back in the days of its decline, no shirker from the global limelight.
Finally, before I conclude, I would like to mention one last thing about the tree: its wood is not terribly useful, because of its twisting and spidery habit, but it is a very hard and dense wood, and therefore serves excellently as a firewood, producing more BTUs per cord of wood than do the vast majority of other trees, though it is still not quite at the level of the hickories, who are veritable satanic lords of flames.
In conclusion, let me reiterate that G. triacanthos is one of the trees I love best, so mayhap I may be excused my excessively long essay about it. I love its combination of dogged stoicism, eccentricity, and ubiquity. I love the fact that it has become so well-beloved by urban foresters, even though it meets none of the socially acceptable ideas of what a "pretty tree" ought to look like - and this in a field where visual acceptability all too often trumps all other concerns. It is one of the great trees of our continent, and should ye see it (which ye all doubtlessly will, and frequently too!) ye should give it a salute for its conquests and its tenacity!
Saluting conquests and tenacity since 1986,
--mark
These late September days we are currently travelling through are, surprisingly enough, a wonderful time to be a tree-fancier in a big city like Chicago, and that fact is largely the work of this week's tree, Gleditsia triacanthos, the Honey Locust. I have heard this tree's aesthetic called an 'Impressionistic' one, and I cannot deny that this is a perceptive opinion. The Locust's long, feathery leaves, its flattened, squarish, acacia-like crown, and the dappled, shifting light that it lets through to the ground all combine to give one the feeling that one is observing something which better belongs in a painting by, say, Cezanne. But at this time of year, the effect is heightened, for in these early days of Autumn the tree's leaves slowly begins to change from its customary light green into an equally light and airy gold. Passing by them on the street, one falls under the impression that the tree is constantly being struck in suitably dramatic fashion by isolated shimmering sunbeams streaming down from between dense, gray clouds. But no - the Honey Locust requires no star to highlight its beauty, but rather does so by means of its own ingenious internal chemical factories.
Now, those of you who know me well have already heard a great deal about this tree, for it is both one of the trees that I most heartily love and one of the members of our North American sylva which is the most eminently visible to a grime encrusted city-slicker. This second fact is due to its immense popularity as a street tree throughout all of our great nation's major metropolitan areas. In Chicago, it is the single most frequently planted tree along streets both residential and commercial, and I do believe that it can lay claim to that same accomplishment in both New York and Los Angeles. "If you can make it here," they say about New York, "you can make it anywhere." And so G. triacanthos has, not only thriving in the harshest of urban environments, but also being planted in such divers locales as Europe and Australia - in both of which places it has been so successful as to become a major invasive 'weed' species. In Australia, in fact, it has been given the deliriously exciting common name of "McConnel's Curse". Or, at least, so claims Wikipedia.
Why is this tree so incredibly successful as a street tree? Why has it been planted so ubiquitously throughout our nation's major cities? The answer lies in a host of adaptations that the tree has which make it a near-perfect urban survivor. From the perspective of a human forester, one of the tree's chiefest advantages is its rapid growth rate. It might not grow as fast as a cottonwood, but during the first ten years of its life it can spring up at the more than respectable rate of two feet a year, meaning that one can have grown a truly respectable shade tree from a seed in well under two decades - meaning that one does not have to look into the vastly far future when planning neighborhoods around this tree. Furthermore, it is among the most salt-tolerant of trees. In the middle of winter, when tons of salt are poured out on the streets of our cities to prevent the excssive formation of ice slicks, the ability to survive the leaching of all this salt into the soil without being poisoned or losing literally tons of water is very important to a tree, and G. triacanthos can survive even on the edges of freeways which are even more salt-encrusted than a city's residential streets. I should note, though, for the sake of intellectual integrity, that while almost all the sources I have looked at agree on this property of the Honey Locust's, the USDA does not, and I normally treat the Department of Agriculture as among my more unimpeachable of sources. Due, however, to the unanimity, and even enthusiasm, with which my other sources treat this fact (and I include such reliable people as the National Arbor Day Foundation among these sources), I have decided to, for once, disbelieve the USDA. Especially since G. triacanthos so patently does flourish alongside the busiest of downtown streets, and this is a property one would expect of such a tree.
But wait - there's more! The Honey Locust is also tolerant of a wide range of soil pHs. It might not be as acid-loving as, say, rhododendrons or pines, but it is still tolerant of rather acidic soils, and can also survive well in soils that are rather more alkaline than many plants would prefer. Given the odd fluctuations in general soil chemistry likely to be found in an urban area, with all the pollution of a million car exhausts, a thousand factories, and an infinity of sewage pipes settling into the ground, such an insouciant ability to withstand these constantly changing, and generally unpleasant, conditions gives the tree another advantage. Furthermore, G. triacanthos is also able to survive a wide range of temperatures, minding neither the swelteringest hundred-degree days of summer nor the bitterest minus-twenties of the coldest winter. Those of you who, like me, live in Chicago can easily appreciate how essential both of these capabilities are, but you may not fully understand that trees are, like their animal counterparts, very susceptible to their environment's ambient temperature. Birches, for example, will wither and die if exposed for too long to the direct rays of the summer sun, whereas a live oak will quickly give up the ghost if a frost lasts for more than just a few days. But the Honey Locust shrugs off both of these extremes with equal ease. Also shrugged off with ease by this hardy tree are all but the most terrible droughts. Though it prefers a nice, deep, moist soil, and is, in nature, most frequently found in moist but well-drained river valleys, it seems to be unfazed by extended dry spells.
Gleditsia triacanthos is among the easiest of trees to identify, loudly proclaiming itself as 'unique' compared to all other common American trees in a variety of ways. I have already mentioned its fern-like leaves, either singly or else doubly pinnately compound, each seven or eight inches in length, and whose small, oval, spoon-shaped leaflets are all about a half-inch in length. This last fact provides a convenient way of distinguishing between it and the similar leaves of the Water Locust (Gleditsia aquatica) and the Black Locust (Robinia pseudoacacia), both of whose leaflets are much larger, a full inch or two in length. Also very characteristic is the tree's bark, which has a wonderful iron-gray color, and forms large plates along the trunk that are distinctive. The Honey Locust has a spidery growth habit, too, that allows one to identify it even at a distance. The tree rarely grows straight, producing a solid vertical trunk reaching high up into the air, but instead wriggles and twists as it grows, forming a main trunk that seems rather crooked and which soons sprouts out into many large diverging and forking branches. I am told that, in the rich lowland soils which it most delights in, the Honey Locust can reach heights of well over a hundred feet, but I am somewhat skeptical of this claim. Certainly, though, G. triacanthos is a goodly-sized tree, able to grow a solid seventy or so feet without even breaking a sweat. It also can produce a very wide-spreading crown, whose diameter at maturity can be just as great as the tree's height - a full 70'. Its flowers, which are rather small and inconspicuous, are nevertheless a pleasing creamy white or green in color, and appear in late spring, in May and June, and apparently have a reasonably strong and agreeable odor. I confess that I do not recall having ever gone up to smell a Honey Locust's flowers, and so cannot report back to you if this tale is correct, but next spring I will most certainly do so, and would also encourage all of you out there in TV-Land to do the same. Supposedly bees like this flower's scent as well as people, and seek it out, though it is not known as a great honey-producer or flavorer.
The two most distinctive traits of this tree, though, are its fruit and its thorns. Its fruit is a bean - and it is a true bean, for G. triacanthos is a member of the Fabaceae, the bean family which is so mighty and predominates in all of this world's terrestrial ecosystems - that is usually about 8" in length, though they sometimes reach to almost two feet long. These fruits - some of the largest in the entire spectrum of North American trees - begin appearing in early September, and slowly twist themselves into a corkscrew shape before dropping off over the course of the winter, which means that a Honey Locust can, even after all its leaves have dropped, still be covered with twisting red-brown bean pods, each containing some dozen seeds a centimeter or so in length. These seeds are surrounded by a sweet-tasting edible pulp, from which the tree gets the "honey" in its common name. This pulp is well-loved by deer, cattle, and other large herbivores, and is, I am assured, completely edible to people, and was indeed used as food by this continent's autochthonic inhabitants, who also fermented it to make a beer. I have never tried to eat Honey Locust pulp, but I certainly do plan on it. I feel somewhat suspicious of the fruit on city-grown trees, for the Lord alone knows what sprays they've used on it and how much of the city's pollution has been absorbed by the tree and passed on to the fruit, but there are several large, handsome Honey Locusts in the yard of my parents' house out in Suburbanland, so the next time I'm there, by God! I'll try me some Locust flesh. As for the thorns, they are truly impressive. Each one can be up to five inches long, and they frequently come in dense clusters along the trunk. These thorns grow straight out of the woody trunk of the tree, making breaking them off a Herculean task. But not all Honey Locusts have thorns, and those that do have them in very different quantities. Some trees are covered with them, whereas others have but a few. The ones most commonly planted in urban areas are from thornless varieties and cultivars (i.e. G. triacanthos inermis, G. triacanthos 'Sunburst', etc.) but it is nevertheless not uncommon to find one with a full set of thorns popping out of its trunk to menace passers-by.
The Honey Locust is a storied tree, with a dramatic history stretching back into the distant past, into the long-vanished era before the everlasting ice of the North rolled over this continent and changed its face forever, before any human eye ever saw any of the continents of this hemisphere. Since those two most characteristic features of the tree - its fruits and its thorns - play a key rôle in this story, it seems fitting to tell that tale at this precise point in my exposition of G. triacanthos' virtues & vices. In that distant pre-glacial epoch, North America was still home to giant animals the likes of which are not to be seen to-day: Saber-toothed cats, mammoths & mastodons, giant beavers(!), cameloids & llamas, dire wolves, cat-faced bears, and, of course, Megatherium, the giant ground sloth, a huge, possibly omnivorous animal that stood twenty feet tall when standing on its hind legs and had claws as long as a human forearm on both its fore and hind limbs. Evolution being the most opportunistic of masters, it is not to be supposed that there were no trees whose phenotypes were adapted specifically to take advantage of these ancient 'Giants in the Earth', and it is now hypothesized by many scientists (excellently summarized by biologist/science popularizer Connie Barlow in her book The Ghosts of Evolution) that the Honey Locust was just such a tree. Consider, for example, its thorns. In these latter days, what purpose could they serve? Do they defend against deer? No, of course not; a deer's head is certainly nimble enough to avoid the dense clusters of thorns on the side of a tree; they are no deterrent against those ruminants. Furthermore, although a young G. triacanthos might have something to fear from deer browsing their leaves, an older example of the species, with most of its limbs well out of reach of the mouth of any cervid, scoffs at the notion of deer posing a threat to its livelihood - and yet will still produce those intimidating thorns. And in the fall, when buck deer so vigorously rub their antlers against tree bark to scrape off dead skin, in the process often mortally wounding the tree that they do this against, the Honey Locust is not at all the sort of plant that they take delight in. They prefer trees whose bark is slippery, like the Willow, not one whose bark is as steadfastly attached to the wood 'neath it as is that of the Locust. So what purpose have these brutal thorns? Obviously, to defend against those extinct titans, the mastodons and Megatheriums who must once have loved the taste of Locust leaves.
Its fruit is also curiously anachronistic in the modern world. It is clear that it co-evolved with some sort of animal to serve as its dispersion mechanism, for Evolution does not go to the trouble of sweetening a tree's fruit with sugary pulp unless that plant has something to gain by it. Furthermore, the seeds that lie waiting within these pods have a coat that is thick enough that the embryo within cannot get access to precious air and water unless the coat is first damaged in some way - say, by being eaten away by the powerful acids inside an animal's stomach. Indeed, it is by being submerged in sulfuric acid for ~1 hr. that G. triacanthos seeds are scarified for commercial propagation today. It is reasonably certain, too, that it must have been larger animals that the Locusts took particular advantage of, for to-day, although squirrels and deer will certainly take advantage of Honey Locust "honey", they do a poor job of seed dispersal, typically either avoiding or eating entirely the seeds contained within the pods. It is, in fact, the farmer's cow who does the best job of dispersing the Honey Locust's seeds, eating the pod whole for its sweet filling, and allowing the seeds to pass straight through its multiple stomachs, its powerful acids properly scarifying the seedcoat before it finally emerges from the cow in the middle of a nice pile of beautiful fertilizer.
So, we have an image of a Pleistocene North America where the Honey Locust co-existed with its predators, the giant herbivorous animals of the time, feeding them with one hand whilst keeping them at bay with the other. Given how successful it is in nature even in these latter days when it is bereft of any reliable dispersal mechanism, it must have been even more widespread in those ancient times. But, when the glaciers finally retreated, and the combined effects of climate change, diseases imported from the East, and the devastating efficiency of a new predator, Homo sapiens, combined to reduce our continent's megafauna to a fraction of what it once was, the Honey Locust must have retreated in its range, and rapidly. For G. triacanthos is not a long-lived tree, paying for its early vigor by expiring after little more than a century of life. So it must have retreated to areas where the deer and squirrels would still offer it their feeble services, though they be but pitiful handmaidens compared to its dashing servants of old, and to where fast rivers would carry away its pods and smash its seeds fearfully enough to break their pods before depositing them in rich loamy soil. But with the spread of sophisticated agriculture to the regions north of the Rio Grande, and the arrival of large Eurasian domestic herbivores (i.e. horses & cattle), the Honey Locust sprang back from its slow slide into oblivion. Spread first by those food and companions of Humanity, the Honey Locust has, in the past half-century, attracted the attentions of mankind itself, and its advantages have (as revealed above) allowed it to co-operate with humanity for the mutual benefit of both species, as G. triacanthos has now been reintroduced into vast regions where once it floundered, and spread to whole new areas where it was previously completely unknown.
Now, as might easily be imagined by the length of this essay, I am getting very tired of typing, and impatient for it to be finished. So I will gloss over the taxonomical relationships of this tree. But do not worry for your lack of information, for this tree is part of a truly mighty clan, the Fabaceae, and I will reveal to you more data about that impressive kingroup in many a later essay about its other arborescent North American scions. Let it suffice to say for now, that G. triacanthos is undoubtedly part of this family, second only to the daisies and orchids in terms of numbers of species, and that it is a member of the Caesalpinieae sub-family (which molecular studies have re-shuffled the membership of significantly, but which clearly includes both Gleditsia genus and the Gymnocladus genus, another prominent member of the North America's sylva). Let it further be said that, like most members of the bean family (for the Fabaceae is indeed the family that includes everything from lentils to peas to lima beans), G. triacanthos is an expert at obtaining nitrogen from its environment, both entering into even more complex relationships with mycorrhizas (root fungi) than do most trees, and also providing, amongst its roots, tiny nodules in which form a home for certain soil bacteria that exchange nitrogen that they 'fix' from atmospheric sources for sugar that the tree feeds them. This capability of beans makes them important players in ecological cycles worldwide, and G. triacanthos is thus, even back in the days of its decline, no shirker from the global limelight.
Finally, before I conclude, I would like to mention one last thing about the tree: its wood is not terribly useful, because of its twisting and spidery habit, but it is a very hard and dense wood, and therefore serves excellently as a firewood, producing more BTUs per cord of wood than do the vast majority of other trees, though it is still not quite at the level of the hickories, who are veritable satanic lords of flames.
In conclusion, let me reiterate that G. triacanthos is one of the trees I love best, so mayhap I may be excused my excessively long essay about it. I love its combination of dogged stoicism, eccentricity, and ubiquity. I love the fact that it has become so well-beloved by urban foresters, even though it meets none of the socially acceptable ideas of what a "pretty tree" ought to look like - and this in a field where visual acceptability all too often trumps all other concerns. It is one of the great trees of our continent, and should ye see it (which ye all doubtlessly will, and frequently too!) ye should give it a salute for its conquests and its tenacity!
Saluting conquests and tenacity since 1986,
--mark