Gleditsia triacanthos - honeylocust, widely adapted temperate zone fodder tree

Well known as an ornamental street tree, honey locust was widely advocated as a livestock feed early in the 20th century. Silvopastoral cultivar development began in the 1930's at the Tennessee Valley Authority in the United States. Because it can provide a source of fodder, protein, energy, and erosion control, honey locust is being tested in many temperate, Mediterranean and highland tropic regions of the world.

Botany

Gleditsia triacanthos L., family Leguminosae (subfamily Caesalpinioideae), attains a normal height of 15-25 m and 0.51.0 m diameter (maximum height 50 m, diameter 1.8 m). Trees have a short bole and open, narrow or spreading crown with reddish brown to black scaly ridged bark, often covered in clusters of large, branched thorns. Leaves are 10-20 cm long, deciduous, pinnate or bi-pinnate with 15-30 leaflets, 1-3 cm long (Harrow et al, 1996). Flowers are a pale-yellow to greenish-yellow color and appear from early May in the southern United States to late June in the north. Seeds are 0.5 to 1.5 cm long, dark brown in color, smooth, with a hard, impermeable seedcoat. Seeds ripen from mid-September to late October in the United States. Mature pods begin to drop by mid-September and continue to drop throughout the winter.

Ecology

Within the natural range, a large amount of variation exists in both climate and soil conditions. Honeylocust occurs naturally in humid and subhumid climate regions. Average annual precipitation varies from 510 mm to 1520 mm, the frost-free period varies from a minimum of 150 to 300 days (Blair, 1990). Honeylocust grows naturally to 760 m but has been planted from sea level to 1,500 meters in temperate latitudes and will grow above 2,500 m in subtropical highlands.

Honeylocust is a shade intolerant tree, and will only become established in openings. It has a strong taproot and profusely branched root system. Its best growth in the United States is found on deep soils (pH 6.0 to 8.0) in moist, alluvial floodplains between 35° and 40° N. latitude. It generally grows poorly on gravely or heavy clay soils and often fails on shallow soils (Blair, 1990). Honeylocust is resistant to both drought and salinity, and coppices vigorously when cut.

Distribution

Honeylocust grows naturally in the eastern half of the United States (Blair, 1990). It has become naturalized east of the Appalachian mountains from Georgia to New England in the East, and north to South Dakota in the West (Harrow et al, 1996). As a fodder tree, Honeylocust is being tested in France, Spain, Germany, Greece, Algeria New Zealand, Australia South Africa India Bhutan, Nepal and Guatemala (Wilson, 1993).

Gleditsia triacanthos

Uses

Silvopastoral Agroforestry.

Honeylocust pods have long been recognized for their animal fodder value in silvopastoral systems (Scanlon, 1980). Widely spaced overstory fodder trees (fodder orchard), can be planted for on-farm silvopastoral systems, providing light shade, soil enrichment and stabilization, and should be compatible with a variety of forage, grain, vegetable, woody perennials or animals in the understory. In addition to yields from understory enterprises, the pods function primarily as a late fall/winter animal feed supplement (Wilson, 1993). In France, results from sheep feeding trials using pods as a feed supplement indicate that selected grafted clones produce high quality fodder and good weight gain (Dupraz and Baldy, 1993). Sheep are able to digest the majority of seeds within the pods. However, for complete utilization by sheep, cattle, horses or swine, pods and seeds must be machine processed.

Leaf Fodder.

Honeylocust leaves are an excellent source of fodder, contain 20 percent crude protein, low lignin and ensile well. Coppice regrowth retains high protein and low lignin levels (Baertsche et al, 1986). However, limited studies indicate very low biomass yield response when planted from seed and harvested with a forage harvester during the first year's growth (Gold. 1984) or when 1-year-old seedlings were coppiced (at age 2) after a full year for establishment and growth (Addlestone, 1996).

Wood.

Strong, hard and durable. resistant to shock, with attractive figure and reddish-brown color, it is used locally for fence posts, pallets, crating, general construction, railroad ties (Panshin and De Zeeuw, 1970) and by woodworkers for making guitars (A. Wilson, pers. comm). Wood specific gravity is 0.60 green, 0.67 ovendry (Panshin and De Zeeuw, 1970), and is considered an excellent source of fuelwood.

Ornamental.

It has been widely planted as an ornamental replacement for American elm in the United States and Canada with over fifty recognized cultivars (Santamour and McArdle, 1983). Thornless trees can be produced by budding with scionwood taken from the thornless upper branches of selected cultivars. However, seedlings from such trees are thorny. Thornless seedlings can be selected at a very early age (within ten weeks of germination) for use as ornamental cultivars.

Windbreaks.

Honeylocust is hardy and drought tolerant, and can be-grown in windbreaks with the added benefit of pod production.

Silviculture

Propagation.

Mature pods can be collected after they drop off, by hitting branches to jar the pods loose, or by clipping pods from the branches. After harvest, pods should be stored at 0° C to prevent fermentation of the pods and. if bruchid seed weevils (Amblycerus robiniae) are present in the pods, it will prevent them from spreading within the pods. A good pod crop can exceed 20 kg of cleaned seed per tree. Results from a rangewide provenance/progeny test show that seed yield averages 5,200 seeds/kg (varying from 3,300 to 14,300 depending on the seed source) with high purity and soundness.

To prepare pods for mechanical seed extraction, place them in a convection/seed drying oven for at least 2 hours at 35° C. Honeylocust seed will remain viable for many years if stored dry at 1-4° C. Successful germination requires seed scarification via immersion in concentrated sulfuric acid (60 120 minutes followed by thorough rinsing), hot water (82°C), or by mechanical means. Germination of sound seed should be in the range of 75-95 percent. Seeds should be sown.5 to 1.5 cm deep and if properly scarified, complete germination will occur within 21 days of sowing.

Establishment

For successful in propagation of honeylocust, chip budding with green wood in August works best, and June budding is also satisfactory. Dormant scionwood results in a low percentage of successful grafts (pers. comm. A. Wilson).

One-year-old seedlings (or budded/grafted material) can be outplanted the following spring. Dormant, nursery grown seedlings can be stored, barerooted, at about 0° C for several weeks before outplanting. Due to large variation in pod production from different parent trees, and the presence of both male and female trees, only grafted seedlings are recommended for planting in order to secure consistently high production at an early age. Grafted seedlings begin to bear pods at age three and by age eight will produce 20-75 kg dry weight per tree (Wilson, 1993).

Management

Male trees (about 10%) must be included in or adjacent to fodder orchards to ensure pollination of female trees. When established in working pastures,young trees need protection via plastic tree shelters or electric fencing (Wilson, 1993).

Appropriately managed, average annual pod production at age 10 of 40 kg/tree appears feasible. Planting 75 trees/ha (excluding male trees) would yield 3,000 kg/ha, sufficient to provide 100 sheep a 1.5 kg ration of pods for 20 days. Using conservative yield estimates from grafted trees, economic analyses indicate internal rates of return varied from 9 - 13% (Wilson, 1991).

Symbiosis

Typical of many caesalpinioid genera. Gleditsia triacanthos do not nodulate and lack an ability for symbiotic fixation of atmospheric nitrogen (Allen and Allen, 1981).

Limitations

Thorns on mature trees (twigs, branches and bark) are extremely dangerous as they can puncture tractor tires and injure livestock and increase the difficulty of orchard/windbreak management. Volunteer reproduction of thorny seedlings, usually derived from seeds eaten and not digested by wild and domestic animals. is also a concern. The mimosa webworm, Homadaula anisocentra is a serious defoliant and heavy infestations of spider mites (Eotetranychus multidigituli) occur during dry weather and can also defoliate a tree (Blair, 1990).

Research

Research needs include additional production data from silvopastoral systems, development of consistent, heavy bearing, genetically thomless, high protein cultivars for a range of sites and end uses; and development of high sugar varieties for ethanol production (Gold and Hanover, 1993).

Principal references

Baertsche, S.R., M.T. Yokoyama, and J.W. Hanover. 1986. Short rotation, hardwood tree biomass as potential ruminant feed-chemical composition, nylon bag ruminal degradation and ensilement of selected species. I. Anim. Sci. 63:20282043.

Blair, R.M. 1990. Gleditsia triacanthos L. Honeylocust. ln: R.M. Burns and B.H. Honkala, Tech. Coordinators. Silvics of North American Trees, vol. 2 Hardwoods. USDA Handbook 654. pp. 358-364.

Dupraz, C. and C. Baldy. 1993. Temperate agroforestry research at INRA, Montpellier, France. In R.C. Schultz and J.P. Colletti, eds. Opportunities for Agroforestry in the Temperate Zone Worldwide: Proceedings of the Third North American Agroforestry Conference. August 15-18, 1993. Ames, lowa U.S.A. pp. 445-449.

Gold, M.A. and J.W. Hanover. 1993. Honeylocust (Gleditsia triacanthos L.): Multipurpose Tree for the temperate zone. International Tree Crops Journal 7(4): 189-207.

Harlow, W.M., E.S. Harrar, J.W. Hardin and F.M. White. 1996. Textbook of Dendrology. Eighth Edition. McGrawHill, Inc. New York. 534 p.

Wilson, A.A. 1993. Silvopastoral agroforestry using honeylocust (Gleditsia triacanthos L.). In R.C. Schultz and J.P. Colletti, eds. Opportunities for Agroforestry in the Temperate Zone Worldwide: Proceedings of the Third North American Agroforestry Conference. August 15-18,1993. Ames, lowa U.S.A. pp. 265-269.

A complete set of references is available from FACTNet

FACT 96-02 January 1996