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Silvopasture Tree Species: Honey Locust (Gleditsia triacanthos)
Many nasty, thorny specimens of Honey Locust grow wild in my pasture already so the many agricultural uses of this tree have gotten me quite excited.
Nitrogen Fixation
First off, Gleditsia triacanthos is a leguminous tree meaning it fixes nitrogen into the soil from the atmosphere. Most legumes complete this process through a symbiotic relationship with bacteria performed through root nodules. But wait, honey locust does not have root nodules and thus cannot fixate nitrogen?
That has been the scientific consensus since the lack of root nodules on these trees was documented. However much evidence is being made apparent that even non-nodulating legumes fix nitrogen via a process that is not yet understood. It is actually a very controversial subject that has been fun to track. This 1996 Honey Locust Newsletter from the University of Virginia department of agroforestry documents the first scientific dispute to the idea that non nodulating legumes cannot fix nitrogen. Summarized, Jim Bryan in his 1995 doctoral dissertation at Yale’s Forestry department found evidence that Honey Locust (among many other non-nodulating legumes) fix nitrogen. His finding were confirmed in this 2006 issue of the same publication,
Direct evidence was also noted that Honey Locusts fix nitrogen in this laughably expensive source.
Honeylocust leaves and seeds contain more nitrogen than they should. Even higher than nodulating legumes at the same site (another paywalled source) which brings me to the next point.
Leaf Drop
Honey locust leaves are high in nitrogen and their small size means they are quickly broken down then incorporated into soils providing an improvement. Similarly the
Form
of Gleditsia is one that minimizes the shading of pasture and resulting decrease in growth of pasture grasses. The same small leaflets and open form of the tree provide some shade that cools the pasture and lessens water loss from evaporation without blocking all light. The following image shows a tree nearing maturity and the tendency for grasses to grow right up to the trunk.
Fruit Bearing
Honey locust is a regular bearer and rarely fails to crop for a year. In fact, every second year the fruit yield is massively increased. The tree produces from the age of 3 to the age of 100 years old (Source). Average annual production for 9-10 year old ‘Millwood’ and ‘Calhoun’ cultivars was 59kg according to a 1940s Auburn University study (source). Pigs, birds, goats sheep and cattle all relish honeylocust pods but sheep and [maybe] goats are the only animals to fully digest them. The large size of the pods makes them very easy to gather and they reportedly store identically to grains. Livestock that cannot fully digest the pods will disperse the beans via manure.
With some processing, sugar is easily extractable from the pods for use in food, beverages and fermentation. The waste of this processing is molasses rich fodder for livestock.
Miscellaneous
Sprouts from undigested beans in undesirable locations can easily be moved as honey locust is easily transplanted. Root suckers and grafts are both well suited to this tree and clone the genes of the parents tree. So heavy producers can be cloned for the rest of the pasture. Honey Locust leaves and the soft thorns of young plants are also a great food source for grazers. Direct browsing or cut and carry of leaf filled branches utilize unwanted saplings. Additionally the tree grows very fast and produces early (3 years after planting).
The roots and form of the tree also contribute significantly to eliminating soil erosion from precipitation and wind. Similarly, North-South rows of the trees are effective windbreaks in pastures. Honey Locusts are well adapted to even the poorest and rockiest soils.
Bottom Line
Soils classified as rocky outcrop are extremely well suited for the honey locust trees. As the goal of my pasture management is to build soil quantity over the exposed limestone, the roots will help hold soils in place as they are build and the leaf litter will supply nitrogen-rich biomass. Over 100 pounds of fodder loved by my livestock that is dropped by each tree is a bonus that negates any negative effect the shading of the trees has on pasture grasses. Lastly, if the trees don’t work out for whatever reason, I have hard high-quality timber to harvest.
The pasture is full of these trees already and I have personally watched deer devour the bean pods. It is already a perfect fit without any management efforts.
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