HONEYLOCUST RESEARCH NEWSLETTER No.3 September, 2006
Table of Contents
Past editions of the Newsletter, plus articles and bibliographies on agroforestry using honeylocust are now available online at:
As reported in the last issue of the HR Newsletter, research by Dr. Jim Bryan at the School of Forestry at Yale University found evidence of bacterial nitrogen fixation in the roots of non-nodulating Leguminosae. These results, now expanded and reported in the refereed journal, Plant and Soil, included tests with Gleditsia triacanthos L. and twelve other non-nodulating species under different growing conditions--potting soil, sand, and bare root. Subsequent to the publication of this article, additional tests by Bryan using Gleditsia triacanthos L. have further confirmed the earlier findings.
Tests for bacterial activates in non-nodulating species were conducted with an electronic scanning microscope (SEM) and by ethylene evolution using acetylene reduction as an indication of nitrogenase activity. All 13 non-nodulating species tested showed positive results with both the SEM and ethylene evolution.
Previous to Bryan's work nodulation was assumed to be a necessary condition for the fixation of atmosphere nitrogen. Bryan et.al. hypothesize an evolutionary continuum between precursor non-nodulating, 'primitive' members of the Caesalpiniodeae family (including the genus Gleditsia), and the more sophisticated nodulating members of the Papilionoideae and Mimosoideae families. Supporting this hypothesis Bryan found:
--"Non-nodulating species of the Leguminosae grow well in many nitrogen-limited soils, as do nodulating legumes."
--"Non-nodulating leguminous trees dominate many poor sites and out produce nodulating species on a variety of sites."
--"Tissues of both nodulating and non-nodulating species tend to be rich in nitrogen compared with non-legumes."
--non-nodulating legumes "...had higher leaf nitrogen concentrating than plants of most other [non-legume] families in the sites studied."
--"Such non-nodular nitrogen-fixation would have provided an environmentally based predisposition for the evolution of the nodular symbioses." (Bryan pp. 155-157)
[Bryan, James A., Graeme P. Berllyn and John C. Gordon. 1996. Toward a new concept of the evolution of symbiotic nitrogen fixation in the Leguminosae. Plant and Soil. 186:151-159.]
Virginia Technical University and USDA/Agricultural Research Service are cooperating on a silvopastural agroforestry experiment using honeylocust and black walnuts. The initial results of their study as reported in the journals Agroforestry Systems and Agronomy Journal are summarized below. These trails are continuing with animals introduced into the paddocks.
[Bendfeldt,E.S., C.M. Feldhake, and J.A. Burger. 2001. Establishing trees in an Appalachian silvopasture: response to shelters, grass control, mulch, and fertilization. Agroforestry Systems 53:291-295.]
Abstract, p. 291 "In order to successfully introduce trees into existing pastures, it is important to determine and recommend a whole range of tree establishment practices. In the spring of 1995, approximately 350 bare-root seedlings each of black walnut (Juglans nigra L.) and honeylocust (Gleditsia triacanthos L.) were planted in six randomized paddocks within a silvopastoral study area at the Agroforestry Research and Demonstration Site in Blacksburg, Virginia. Three seedling establishment studies were tested, including (1) a tree protection study, (2) a water retention study, and (3) a fertilization study. Seedlings were planted using two different tree shelters (60 cm-tall poultry wire cage and 1.2 m-tall plastic Tubex), two water retention treatments (mulch and herbicide spray), and one fertilizer treatment. All treatments were compared to untreated controls. Tree survival, damage, and stem volume were compared for each species. Tree survival was comparable among all studies over three growing seasons. Tree establishment using poultry wire and Tubex shelters resulted in significant reduction of deer damage and significant increase in stem volume in 1996 to 1998. Tubex shelters had a pronounced positive impact on tree height and also on stem form; height of both black walnut and honeylocust was twice the height of control seedlings. Mulch and herbicide treatments for moisture control resulted in significant stem volume increases over the control treatment from 1996 to 1998. However, mulching was less effective than the herbicide treatment. There was no significant tree growth response resulting from fertilization during this period."
[Buergler, A.L., F.H. Fike, J.A. Burger, C.R. Feldhake, J.A. McKenna, and C.D. Teutsch. 2005. Botanical composition and forage production in emulated silvopasture. Agron J. 97:1141-1147.]
Abstract, p.1141 "Integrating trees into pasture may increase pasture production and improve nutritive value by altering both species composition and productivity. Our objective was to determine forage yield and botanical composition in response to tree species, tree density, and slope position in an emulated silvopasture....Sampling sites (n = 54) under field treatment combinations were harvested May to October at 35-d intervals in 2002 and 2004. Before spring, summer, and fall harvests, plots were subsampled for botanical composition. Tree species did not affect botanical composition when compared over the two seasons. Plots under honey locust trees tended to have more fescue in a dry year (2002) and more legumes and less dead herbage in a wet year (2003). Greater percentages of warm-season grasses and fewer weeds were observed at low tree density sites in 2003. Forage mass (5200, 6130, and 4970 kg ha-1 at low, medium, and high tree densities) was 16% greater under medium-density trees. Plots under black walnut yielded 13% more forage than those under honey locust (5790 vs.5130 Kg ha-1). Appropriately spaced trees have potential to positively alter botanical composition and can support greater forage production in a southern Appalachian silvopasture."
Results, p. 1144 "Trees in the study were 10 yr old and approaching full canopy closure in the closest row spacing by the end of 2003. Average height across density and slope treatments was 3.2 m for walnut and 5.1 m for locust trees."
Conclusions, p. 1147 "Our data indicate that with appropriate spacing, incorporation of black walnut or honey locust trees into pastures can alter botanical composition and forage production in southern Appalachia. Given that forage yields peaked at medium tree densities and that light levels under low tree densities were not dissimilar to open areas, our data suggest that incorporating walnut or locust trees could boost forage production over that of open pastures. Positive yield response depends on the maintenance of appropriate tree density, however.
"While both tree species appear compatible with forage production systems in southern Appalachia, honey locust may not be as effective in promoting increased forage production, particularly at sites with lower rainfall. However, greater amounts of legume and lesser amounts of dead herbage and tree leaves in swards under honey locust trees suggest this species may have benefits for forage nutritive value in mixed pastures."
[Buergler, A.L., F.H. Fike, J.A. Burger, C.R. Feldhake, J.A. McKenna, and C.D. Teutsch. 2006. Forage nutritive value in an emulated silvopasture. Agron J. 98:1265-1273.]
Abstract, p.1265. ...Concentrations of neutral and acid detergent fiber (NDF, ADF), and acid detergent lignin (ADL), crude protein (CP), total nonstructural carbohydrate (TNC) and Ca, P, Mg, and K were determined. Few differences due to treatment were observed for NDF and ADF concentrations. Concentrations of TNC decreased with greater tree density and appeared to follow tree left growth. Crude protein concentrations were typically greater under honey locust trees. Forage mineral concentrations frequently were greater with increased tree density. Trees appear to have both positive and negative effects on forage nutritive value, and their effects on animal performance warrants further research.
Steven Sharrow at Oregon State University in Corvallis, Oregon, USA tested the effectiveness of establishing honeylocust in pastures using plastic shelter tubes (152 cm tall) and rigid plastic mesh tubes(88 cm tall). Honeylocust was compared with black locust and honey mesquite (100 plants each) grown with the plastic tubes, the mesh tubes, and a control.
[Sharrow, S.H. 2001. Effects of shelter tubes on hardwood tree establishment in western Oregon silvopastures. Agroforestry Systems 53: 283-290.]
Abstract, p.283: "...Initial tree survival during the first summer and winter following planting was higher in shelter tubes than in mesh tubes. At the end of the third growing season, 58%of the black locust and 94% of the honey locust trees in shelter tubes were still alive ... honey locust height growth was increased by 300% and diameter growth was increased by 150% compared to tree in mesh tubes. However, shelter tube trees tended to be taller relative to their diameter and had difficulty standing upright if tubes were removed.
Five recent developments lead us to be optimistic concerning future prospects for silvopastural agroforestry using honeylocust. Reliable data on pod production at various locations remains the missing piece to the puzzle.
1)Weight gains for sheep. In feeding trails with honeylocust pods, Dupraz, et.al. in Montpellier, France have demonstrated high weight gains for sheep.(see article below). These trails also demonstrate that sheep do digest a high percentage of honeylocust seeds. The sheep reproduction cycle also coincides with pod production: pods can be fed appropriately in autumn to flushing ewes or weaned lambs.
2)Tree establishment practices. The favorable results achieved at Virginia Tech and Oregon State (see above), and Montpellier, France using plastic tree shelters, plastic woven-wire protection, and/or electric fencing, etc to establish silvopastural honeylocust orchards. The experience of the UK Agroforestry Network in the United Kingdom introducing trees to sheep pastures is also relevant. Plastic wire cages preferred over plastic tree shelters when trees introduced to sheep pastures. Alternative scenarios include planting trees in hay fields with animals having access only during autumn pod drop, or machine harvesting and processing for feeding to cattle or seine.
3)Clonal propagation. The greenwood budding propagation techniques now available should lower costs of establishing honeylocust orchards.
4)Nitrogen fixation. The strong possibility that Gleditsia triacanthos L. is after all a nitrogen fixing species. While in itself nitrogen does not improve the economics of silvopastural honeylocust, it may attract additional attention.
5)Urban honeylocust. Because honeylocust has been planted extensively on several continents as a temperate zone urban shade tree, a large literature exists on propagation, planting, fertilization, and disease and insect control. A literature search in the Commonwealth Agricultural Bulletin data base for the years 1972‑1992 found 295 entries for G. triacanthos L. This literature is available to facilitate adoption of honeylocust in agroforestry settings.
Christian Dupraz and his coworkers at the plant breeding station of the National Institute for Agronomic Research (INRA) near Montpellier, France, have carried out comprehensive research on several aspects of honeylocust agroforestry. Their published results on (1) pod feeding trails with sheep, (2) pod production from clonal orchards, and (3) bibliography are summarized below.
(1)Honeylocust Pod Feeding Trails
Summary. The pod feeding trails produced encouraging results: sheep fed a daily ration of 1.4kg of whole honeylocust pods gained 135g/day (1993 trails) and 178g/day (1994 trails). In a mixed diet, honeylocust pods have a high nutritive value and can provide sheep with between 25 and 50% of the required organic matter. (Foroughbakhch, 1995) Dupraz concludes that "Gleditsia pods may therefore cover not only maintenance requirements but also production needs."
Methods. Pods from four cultivars selected in southern France ('MIL','TOT','VFM', and 'SUM', acronyms are abbreviated initials of site origins) were compared with each other and with a standard diet. Six castrated sheep were fed in individual cages in 1993.
To measure pod degradability in sacco, three fistulated sheep were used in 1994. After a 17 day familiarization period, each cultivar was fed exclusively for one week. Sheep were initially fed 1000g/day of pods which was increased to 1380g by the 14th day. Pod digestibility coefficients for dry matter, organic matter and crude protein were obtained for in vivo, in vitro (with alfalfa [378g] and mineral supplement[50g]), and in sacco. To obtain in sacco data ground pods and a standard diet were compared by placing feed in a nylon bag for 48 hours in the rumen of fistulated sheep.
Results. After two days of acclamation, sheep ate their entire pod ration. As the experiment progressed, some sheep reversed their initial reaction and increasingly preferred pods to alfalfa. Over the 7 week trail, net weight gains averaged 8 to 14kg/animal. During the one week ad libitum period, sheep ingested 1.9kg pods/day and gained an average of 260 to 820g/day.
In sacco coefficients of whole pod digestibility were high (77.9% compared to in vitro (70.0%) and in vivo (54.8%). In vivo rumen retention times were believed to be lower than the 48 hour in sacco period. Digestibility was inversely correlated with the number of pods ingested. (Hauad) The hard seed coat and rapid passage of the seed through the rumen resulted in incomplete digestibility.
Higher in vivo digestibility could be achieved by:
1) feeding pods with a bulky feed (which would happen naturally in a silvopastural setting), and
2) propagating cultivars with softer seed to improve digestibility and increase protein digestibility (to as high as 70 to 80%). Depending on the clone, undigested seeds ranged from a low of 12% to a high of 33%. A technique to identifying softer seeded varieties is indicated.
Feeding whole pods is preferred to ground pods because of the higher digestibility (due to longer retention time), and avoidance of extra processing costs.
Nutrition. The coefficients of digestibility varied by cultivar and were highest for 'TOT': dry matter (58.7 +/-8.5), organic matter (61 +/-8.4), acid detergent fiber (37.7% +/-10.6). (Foroughbakhch,1998) The in vivo nitrogen content for 'MIL' was: ingested raw protein (147.6 =/-7.0), raw protein coefficient of digestibility (37.3 =/-5.3) (Dupraz and Newman). In vivo crude protein digestibility was 39% for the best variety. (Dupraz and Newman)
A seed budget was calculated for each cultivar and each animal based on seeds per day per animal as follows:
seeds in the ration distributed to animals(p.66,Table 31 average for six animals) - seeds not swallowed + seeds spat during rumination = seeds entering the rumen - seeds in feces - number of seeds in the intestine.
The seed budgets were used to deduce in vivo digestibility ratios. Pod degradability was in vivo (55%), in vitro (70%) and in sacco (78%) and was higher than nitrogen enriched straw.
(2)Pod Production from Honeylocust Orchards
Summary. Five clonal honeylocust orchards (440 trees total) were established in France (3) and Greece(2) between 1987 and 1992. Despite earlier data indicating high pod yields, pod production in these studies was disappointingly low. Results from the origin orchard in France are reviewed below.
Methods. At the primary location (in Montpellier, France), a 16-clone honeylocust orchard of grafted trees was established for a germplasm study in 1987. One hundred and forty four grafted trees arranged in a randomized latin square design of 9 blocks (16 trees each) were planted at 5m X 5m spacing (equivalent to 400 tree/ha). With the exception of the U.S. cultivar 'Millwood', selections were from southern France. A border of seedling honeylocust was planted to assure uniform conditions.
Pod Production. The Montipeller orchard yields varied widely among varieties and between years. In year 10 the most productive grafted trees produced 1.8kg DM per tree, the equivalent of 0.7t DM/ha in a 400 tree orchard. These yields were considerably below that expected based on:
--yields at age three of 1.2 kg per tree from highest producing trees,
--earlier production of parent trees,
--average annual production for 9-10 year old Millwood and Calhoun cultivars was 59kg from a 1940s Auburn University study.
Reasons for the lower than expected yields are unclear. The orchard location was judged a "low fertility site" (****checks with funks) (soil was "shallow, plain, with clay texture, and contain a very high proportion of rock"). Neither irrigation nor fertilizer was used. Grass competition, drought condition, and close tree spacing may also have contributed to low yields. A grass intercrop (Festuca arundinacea) was planted for forage production and weed control. After a grass sward was planted the trees grew more slowly. Grass production was equivalent of 2t DM/ha/year.
Other findings from the INRA study include:
Pod retention. Pod retention can be important for providing an inexpensive feed source in late winter. Significant differences in pod retention between trees were observed although 80% of the pods had dropped by early November.
Pod morphological characteristics. Considerable morphological differences in pods (length, width, number of seeds)between cultivars were measured.
Parental tree production. Alternative annual bearing predominated, but erratic patters in some cultivars and regular production in one cultivar were noted. Pod bearing patterns were found to be endogenous rather than climate controlled. Pod size was usually related to site characteristics (soil fertility, water availability and microclimate). One clone changed from producing pods(female flowers) to producing only male flowers and changed again to production of pods.
Alternative bearing. Alternative pod bearing patterns were confirmed with cultivars in opposite phase facilitating annual bearing from a mixed clonal orchard.
Grecian fodder orchard. An irrigated fodder tree orchard of honeylocust (grafted, black locust (Robinia pseudoacacia L.), and mulberry (Morus alba L.), was established in northern Greece in 1991 to compare the species at three different tree spacings and two tree protection devices (Options, pp 72-74). In the first two years, honeylocust grew significantly slower than black locust and mulberry at all spacings. Honeylocust showed high mortality (10% in the first year, 28% in the second year) and was judged "...not a suitable species for semi-dry environments with sandy soils a...". Honeylocust grew faster in plastic tree shelters compared to wire nets, but the differences were not statistically significant.
Growth of grafted trees in a comparable clonal orchard in Greece was "disappointing and slower than anticipated."
Cultivars from this experiment are expected to be commercially available.
Ainalis, A.B., and C.N. Tisouvaras. 1998. Forage production of woody fodder species and herbaceous vegetation in a silvopastoral system in northern Greece. Agroforestry Systems. 42:1-11.
Dupraz, C. 1999. Fodder trees and shrubs in Mediterranean areas: browsing for the future? pp. 145-158. Grasslands and Woody Plants in Europe. Eds: V.P. Papanastasis, J. Frame, A.S. Nastis.
Volume 4 Grassland Science in Europe.
Dupraz, C. and C. Baldy. 1994. Temperate agroforestry research at INRA, Montpellier, France. Schultz, R.C. and J.P.Colletti (eds.) Opportunities for Agroforestry in the Temperate Zone Worldwide. Proceedings of the Third North American Temperate Agroforestry Conference. August 15-18. Ames, Iowa. pp.445-449.
Dupraz, C., Cordesse, R. and Foroughbakhch, R. 1999. Digestibility of honeylocust (Gleditsia triacanthos) pods as measured with three independent techniques. In: Dupraz, C. (ed.) Establishment and Management of Fodder Trees Plantations. INRA, Montpellier.
Dupraz, C. and S.M. Newman. 1997. Temperate agroforestry: the European way. In: A.M.Gordon and S.M.Newman. Temperate agroforestry systems. CAB International. Wellingford, U.K.
Foroughbakhch, R., L.A. Hauad, M.H. Dadii, C. Dupraz. 1995.
Alimentary value of Gleditsia triacanthos seeds. Nitrogen Fixing tree Research Reports. 13:54-57.
Foroughbakhch, R., L.A. Hauad, C. Dupraz, M.H. Dadii. 1992. Sheep utilization of pods of Gleditsia triacanthos L.Phyton 19(1/2): 71-76.
Foroughbakhch, R., L.A. Hauad, C. Dupraz, R. Cordesse, M.H. Dadii. 1995. Pod yield of 16 accessions of Gleditsia triacanthos. Nitrogen Fixing tree Research Reports. 13:58-5.
Foroughbakhch, R., L.A. Hauad C. Dupraz, M.H. Dadii. 1997. Multipurpose and germplasm collection of Gleditsia triacanthos L.
Foroughbakhch, R. 1992. See above. 19:95-
Hauad, L.A., R. Foroughbakhch, M.H. Dadii, C. Dupraz. 1998. Digestibility of Gleditsia triacanthos L. pods. Pyton. 62(1/2):87-93.
Papanastasis, V.P., C.N.Tsouvaras, O. Dini-Papanastasi, T. Vaitsis, L. Stringi, C.F.Cereti, C. Dupraz, D. Armand, M.Meuret, and L.Olea. 1999. Selection and utilization of cultivated fodder trees and shrubs in the Mediterranean region. Centre International de hautes Etudes. INO Reproducciones, S.A. Zaragoza, Spain.
Eighteenth century US Presidents George Washington and Thomas Jefferson shared an interest in honeylocust. At his Mt. Vernon, Virginia plantation, Washington made several plantings of honeylocust to serve as living fences for livestock control. While attending the Constitutional Convention in Philadelphia, Washington wrote to his foreman William Pearce "I will endeavor to procure and send you some honeylocust seed as I conceive very formidable hedges may be made of them." And two weeks later, "I shall send you by the first Vessel at least a bushel and half of clean honey locust seed which I would have raised in a nursery for the purpose of hedging." [Detwiler, S.B. 1947. Notes on honeylocust. USDA, Soil Conservation Service(mimeograph)].
Whether Washington used honeylocust pods for livestock fodder is not known. Richard Henry Lee, another Virginia farmer, wrote to Washington about the benefits of honeylocust pods as fodder (Detwiler, p. 123). Honeylocust presumed to be progeny of those planted during Washington's time can be seen today at the Mt. Vernon plantation on the road from the main house to the barn.
Jefferson was interested in a wide-range of plants, (The greatest service which can be rendered any country is to add a useful plant to its [agri]culture. Memorandum the Jefferson wrote about his services to his country, c.1800). There is no record of his using honeylocust pods for animal fodder. He did however plant honeylocust as ornamental shade trees in an alle along the east carriage lane at his Monticello, Virginia home. These honeylocust were replanted in 1981 in their original locations and can be viewed on a tour of the plantation. It seems likely Jefferson was the first to plant honeylocust as an ornamental shade tree. Interestingly Jefferson selected black locust (Robinia pseudoacacia) as the primary tree for planting on the central lawn of the University of Virginia which he designed.
Higher petroleum prices have increased interest in ethanol production from agricultural crops. In 1980 the US Department of Energy sponsored a conference, "Tree Crops for Energy Co-Production" that included papers on using honeylocust pods as a feedstock for ethanol. Relevant papers from that conference and other bibliography are listed below.
Using honeylocust pods as a base for ethanol production has been proposed by several authors (Williams and Merwin), (Siebert). Given the high pod-sugar content of some cultivars, and considerably lower environmental damage than corn, ethanol production seems promising. Based on pod yields of 1.25 tons(DM)/acre, Freedman estimates a theoretically ethanol production of 81 gallons/acre of ethanol and 0.71 tons/acre (100% dry matter) of fermentation residue(Freedman, p.125).
However, actual fermentation of honeylocust pods has proven difficult. At this point the economics of ethanol production using honeylocust pods is also highly speculative. Uncertainties include information on pod yields and the value of silage residues as livestock feed.
Attempts to ferment pods have to date have not been as successful as hoped for. Ogden attempted to ferment pods using Saccharomyces. Based on limited tests using honeylocust pods as strata for fermentation, ethanol production averaged 5.5 ml/100g for 5 cultivars. The highest cultivar produced ethanol of 7.2 ml/100g. Ogden also found reducing sugar content of the pods to be lower then expected from previous reports.
Avgerinos and Wang fermented honeylocust and mesquite pods using a mixed culture of two thermophilic bacteria. Fermentation for mesquite pods proved satisfactory, while results for honeylocust pods were disappointing. Further research is needed to find bacteria capable of efficient fermentation of honeylocust pods.
Much of the economics of agroforestry honeylocust depends on the success of co-production systems growing honeylocust in livestock pastures or hayfields. If the shade effect is neutral or even positive, then honeylocust pods become virtually a free good(except for establishment and harvesting costs). Given the low pod yields relative to corn, honeylocust should be grown on marginal lands for soil erosion protection.
Bibliography: Honeylocust and Energy Production
Avgerinos, G.C., and D.I.C. Wang. 1980. Utilization of Mesquite and Honey Locust Pods as Feedstocks for Energy Production. In Tree Crops for Energy Co‑Production on Farms. U.S. Solar Energy Research Institute. Golden, Colorado.
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. J. Amim. Sci. 63:2028-2043.
Freedman, D. 1980. Preliminary Analysis of the Potential for Ethanol Production from Honeylocust Pods. In Tree Crops for Energy Co‑Production on Farms. U.S. Solar Energy Research Institute. Golden, Colorado.
Ogden, R.L. 1983. Attempt to ferment sugars in the locust tree bean. Agroforestry Review. 3:5.
Scanlon, D.H. 1980. A Case Study of Honeylocust in the Tennessee Valley Region. In Tree Crops for Energy Co‑Production on Farms. U.S. Solar Energy Research Institute. Golden, Colorado.
Seibert, M., G. Williams, G. Folger and T. Milne. 1986. Fuel and chemical co-production from tree crops. Biomass. 9: 49-66.
Tennessee Valley Authority(1984). TVA biomass fuels update II, TVA OACD-84/3, pp. 13-14. Available from NTIS Springfield, VA pp. 114-118.
Williams, G., and M.L. Merwin. 1983a. Energy‑ and soil‑conserving perennial crops for marginal land in temperate climates. In W. Lockeretz(ed.) Environmentally sound agriculture. Praeger Co., New York, NY.
For bibliography from the research with honeylocust at the National Institute for Agronomic Research (INRA), Montpellier, France, see the article and accompanying bibliography in this HR Newsletter.
Addlestone, B.J., J.B.Mueller, and J-M. Luginbuhl. 1999. The establishment and early growth of three leguminous tree species for use in silvopastural systems of the southeastern USA. Agroforestry Systems 44:253-256.
Alley, J.L., H.E. Garrett, R.L. McGraw, J.P. Dwyer, and C.A. Blanche. 1999. Forage legumes as living mulches for trees in agroforestry practices: preliminary results. Agroforestry Systems 44:281-291.
Bendfeldt,E.S., C.M. Feldhake, and J.A. Burger. 2001. Establishing trees in an Appalachian silvopasture: response to shelters, grass control, mulch, and fertilization. Agroforestry Systems 53:291-295.
Bryan, James A., Graeme P. Berllyn and John C. Gordon. 1996. Toward a new concept of the evolution of symbiotic nitrogen fixation in the Leguminosae. Plant and Soil. 186:151-159.
Buergler, A.L., F.H. Fike, J.A. Burger, C.R. Feldhake, J.A. McKenna, and C.D. Teutsch. 2005. Botanical composition and forage production in emulated silvopasture. Agron J. 97:1141-1147.
Buergler, A.L., F.H. Fike, J.A. Burger, C.R. Feldhake, J.A. McKenna, and C.D. Teutsch. 2006. Forage nutritive value in an emulated silvopasture. Agron J. 98:1265-1273.
Buergler, A.L. 2005. Forage production and nutritive value in a temperate Appalachian silvopasture. M.S. Thesis. Virginia Technical University, Department of Crop and Soil Environmental Sciences.
Burner, D.M., D.H.Pote, and A. Ares. 2005. Management effects on biomass and foliar nutritive value of Robinia pseudoacacia and Gleditsia triacanthos f. inermis in Arkansas, USA. Agroforestry Systems. 65:207-214.
Chong, C. 2000. Response of little-leaf linden and honey locust to rates of organic and mineral nitrogen. Hortscience 5:144.
Csurhes, S.M. and D. Kriticos. 1994. Gleditsia triacanthos L. (Caesalpiniaceae), another thorny, exotic fodder tree gone wild. Plant Protection Quarterly. 9(3):101-105.
Dickmann, D.I.,Gold, M.A., and Flore, J.A. The Ideotype Concept and the Genetic Improvement of Trees for Multiple Purposes. In: Ecosystems of the World: Tree Crop Ecosystems. Elsevier.
Eason, W.R., E.K. Gill, J.E. Roberts. 1996. Evaluation of anti-sheep tree-stem protection products in silvopastural agroforestry. Agroforestry Systems 34: 259-264.
Gold, M.A. and Hanover, J. W. 1993. Honeylocust(Gleditsia triacanthos L.): Multipurpose tree for the temperate zone. International Tree Crops Journal 7(4):189-207.
Gold, M.A. and Hanover, J. W. 1996. Geographic variation patterns in phenological characteristics of honeylocust (Gleditsia triacanthos L). In: Diters M.J. et.al.(eds.) Tree Improvement for Sustainable Forestry. Proc. QFRI-IUFRO Conf., 27 October-1 November 1996. Caloundra, Queensland, Australia, pp.79-80.
Lehmkuhler, J.W., et.al. 2003. Tree protection methods during the silvopastoral-system establishment in midwestern USA: Cattle performance and tree damage. Agroforestry Systems 59:35-42.
Papachristou, T.G., P.D. Platis, V.P. Papanastasis, C.N. Tsiouvaras.1999. Use of deciduous woody species as a diet supplement for goats grazing Mediterranean shrublands during the dry season. Animal Feed Science Technology. 80: 267-279.
Papanastasis, V.P., P.D. Platis and O. Dini-Papanastasi. 1998. Effects of age and frequency of cutting on productivity of Mediterranean deciduous fodder tree and shrub plantations. Forest Ecological Management 110: 283-292.
Paramjet, S., S. Ombir, C. Veena. 1996. Estimating seed quality in hard seeded leguminous trees by accelerating aging and leachate conductivity. Indian-Forester 122: 415-418.
Schoefs, B. 2002. Pigment composition and location in honey locust (Gleditsia triacanthos) seeds before and after desiccation. Tree Physiology 22: 285-290.
Sharrow, S.H. 2001. Effects of shelter tubes on hardwood tree establishment in western Oregon silvopastures. Agroforestry Systems 53: 283-290.
Sperry, C.E., W.R.Chaney, G. Shao, and C.S.Sadof. 2001. Effects of tree density, tress species diversity, and percentage of hardscape on three insect pests of honeylocust. J. of Aproculture. 27:263-270.
Wilson, A. 2002. Silvopastoral Agroforestry Using Honeylocust. 93:55-58. 93rd Annual Report of the Northern Nut Growers Association. East Lansing, Michigan.