Uses
Despite its name, the honey locust is not a significant honey plant. The name derives from the sweet taste of the legume pulp, which was used for food by Native American people, and can also be fermented to make beer. The long pods, which eventually dry and ripen to brown or maroon, are surrounded in a tough, leathery skin that adheres very strongly to the pulp within. The pulp—bright green in unripe pods—is strongly sweet, crisp and succulent in unripe pods. Dark brown tannin-rich beans are found in slots within the pulp.
Its cultivars are popular ornamental plants, especially in the northern plains of North America where few other trees can survive and prosper. It tolerates urban conditions, compacted soil, road salt, alkaline soil, heat and drought. The popularity is in part due to the fact that it transplants so easily. The fast growth rate and tolerance of poor site conditions make it valued in areas where shade is wanted quickly, such as new parks or housing developments, and in disturbed and reclaimed environments, such as mine tailings. It is resistant to Gypsy moths but is defoliated by another pest, the mimosa webworm. Spider mites, cankers, and galls are a problem with some trees. Many cultivated varieties do not have thorns.
Honey locusts produce a high quality, durable wood that polishes well, but the tree does not grow in sufficient numbers to support a bulk industry; however, a niche market exists for honey locust furniture. It's also used for posts and rails since it takes a long time to rot. In the past, the hard thorns of the younger trees have been used as nails.
The honey locust is popular with permaculturalists across the globe, for its multiple uses. The legumes make a valuable, high protein cattle fodder, which becomes more readily accessible with the thornless (inermis) variety. The broad shade of the tree canopy is of great value for livestock in hotter climates, such as Australia. It is also claimed to be a nitrogen fixer, by way of rhizobium, which benefits the surrounding soil and plants. The durability and quality of the timber, as well as the ability to produce its own nails, fits the paradigm of self-sustaining agriculture that requires fewer external inputs/resources.
The ability of Gleditsia to fix nitrogen is disputed. Many scientific sources clearly state that Gleditsia does not fix nitrogen. Some support this statement with the fact that Gleditsia does not form root nodules with symbiotic bacteria, the assumption being that without nodulation, no N-fixation can occur. In contrast, many popular sources, permaculture publications in particular, claim that Gleditsia does fix nitrogen but by some other mechanism.
There are anatomical, ecological and taxonomic indications to counter the assumption that only nodulating legumes fix nitrogen. Many non-nodulating species are as capable as nodulating species of growing well in nitrogen-limited soils and in some cases grow better. Also their leaf litter and seeds are higher in nitrogen than non-legumes and sometimes higher even than nodulating legumes growing on the same site. How this happens is not yet well understood, but current research has recorded by-products of nitrogenase activity in non-nodulating leguminous plants including Gleditsia triacanthos. Also, electron microscopy indicates the presence of clusters around the inner cortex of roots, just outside the xylem, that resemble colonies of rhizobial bacterioids. These may well constitute the evolutionary precursors in legumes for nitrogen fixation through nodulation.
It is not known whether the kind of N-fixation implied by these discoveries benefits other plants in the vicinity, as is known to be the case with nodulating legumes. Gleditsia coppices readily, and it seems reasonable to assume that reduction in root mass in response to coppicing should liberate nutrients in the sloughed off roots into the soil, to the benefit of neighbouring plants.
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