Table of Contents

Nitrogen Fixation in Honeylocust? ………..Page 1

A Thorny Issue: Seedlings in Pastures……Page 2

Honeylocust Breeding Program………………………..Page 3

Projects with Honeylocust Agroforestry…Page 3

Honeylocust Leaf and Twig Fodder……………..Page 4

Honeylocust Beer………………………………………………………….Page 5


Nitrogen Fixation in Honeylocust Roots!?!


"It's never over until it's over." The now-familiar quote attributed to NY Yankee catcher Yogi Bera is as true in scientific investigation as it is in baseball.  Regarding nitrogen fixation in leguminous trees, the conventional wisdom  has been to divide the family into nodule-forming and non-nodulating species, and to assume that those species without nodules do not fix nitrogen.


This conventional wisdom has now been challenged by Jim Bryan in his 1995 doctoral dissertation for the Department of Forestry at Yale University.  Bryan has found evidence that non-nodulating leguminous species apparently do form a symbiotic relation with soil bacteria (Bradyrhizobium spp. or Rhizobium spp.).  This endosymbiosis is carried out directly in the roots of the trees rather than in nodules.  Honeylocust (Gleditsia triacanthos L.) was the primary species used in Bryan's investigation.  


To establish the presence and activity of rhizobial bacteria in the roots of honeylocust, Bryan utilized three techniques: light microscope with stained root slides, scanning electron microscope (SEM), and acetylene reduction.  Each technique indicated the possible presence or activity of the rhizobial bacteria inside the honeylocust root cells.  The electron micrographs of the rhizobial bacteria in honeylocust roots are impressive.  Using the SEM, Bryan also found evidence of bacterial symbiosis in other non-nodulating legume species.


Bryan emphasizes that his research strongly supports, but does not prove, the non-nodule nitrogen fixation.  He is continuing his investigation with acetylene reduction of honeylocust seedlings grown under more exacting conditions (in sand and hydroponically), and is also observing other non-nodulating legumes with the SEM.


Interestingly, Bryan initiated his study from an agroforestry perspective.  He began by cataloging  members of Leguminosae that produce beans (pods) for human consumption.  During this cataloging he found that a disproportionate share of the bean producers did not present nitrogen-fixing nodules.  He then set out to develop a practical test to identify  nitrogen fixing bean producers, and this led him to discover the non-nodule rhizobial symbiosis. 


In the approximately 18,000 member Leguminosae family, Bryan found 277 species which produced beans for human consumption.  Of the 132 species in this group presently tested, 30% did not present nitrogen fixing nodules, compared with only 11% for the family as a whole.  Of the 277 bean producing species, only 9 are native to the temperate zone.

The Gleditsia  genus evolved comparatively early within Leguminosae.  The nitrogen fixing in honeylocust is in several aspects 'primitive' compared to that found in nodulating legumes.  This suggests to Bryan a possible evolutionary continuum within Leguminosae from the non-nodulating species of the Caesalpiniodeae subfamily to the nodulating species.


The implications of Bryan's findings for honeylocust agroforestry are unclear.  How much free nitrogen honeylocust will produce, and how much of that nitrogen will be available for grass production is unknown.  Almost certainly there will be increased interest in honeylocust.  Whether this interest will be justified on the basis of additional free nitrogen will require considerable research.


Bryan, James A. 1995. Leguminous Trees with Edible Beans, with Indications of a Rhizobial Symbiosis in Non-Nodulating Legumes. Doctoral Dissertation, Yale University.

Copies of Jim Bryan's thesis can be obtained from:

University Microfilm International

P.O. Box 1764

Ann Arbor, MI 48106 USA

Telephone: (800) 521-3042

Cost: Microfilm($US32.50);Softcover($US36.50);Hardcover($US43.50)


Page 2

A Thorny Issue: Spreading Honeylocust Seedlings in Pastures


A pasture of thorny honeylocust seedlings is not a farmer's pleasing vision of sustainable agriculture.  Livestock consuming unprocessed pods and defecating the undigested seeds will distribute seeds, and ultimately thorny seedlings, throughout the pasture.  Seeds can also be spread to fencerows and neighboring farms by deer, possum, and raccoons.   For these reasons, many farmers consider honeylocust undesirable and remove them from pastures.


Shawn King at The Bio-Integral Resource Center(see below) write: "We are also  concerned about the capacity of honeylocust to invade riparian areas.  Some of our plantings may rain seed into small watersheds which begin in our pasturelands.  We will be monitoring these areas to evaluate the hazard."


Thornless honeylocust of specific cultivars can be obtained by grafting or budding using scionwood selected from the thornless upper branches of the mother tree.  Nevertheless, seedlings from seeds of these thornless trees will usually present thorns.  For example, seedlings from the cultivar 'Millwood' grown in several US locations have been thorny. 


At present there appear to be only partial solutions to this problem.  While cattle do not digest the seeds, sheep digest approximately 80 percent of the seeds (depending on honeylocust cultivar and sheep breed).  Combining sheep with honeylocust will greatly reduce the problem of unwanted seedlings.  One year old seedlings present green and flexible thorns, and these seedlings are usually eaten by livestock.  Remaining seedlings can be dug from pastures by hand or killed with herbicide.  


As part of an informal survey, I am monitoring five pastures with livestock and fruiting honeylocust.  While I have observed some seedlings, they are largely controlled by livestock grazing.


Page 3

Honeylocust Breeding Program


Jerry Cottingham in Medina, Texas has initiated a breeding program using controlled crosses of four US cultivars.  Cottingham has cross- pollinated and obtained scionwood from the resulting seedlings of: 'Hershey' x 'Ashworth', 'Calhoun' x 'Ashworth', 'Millwood' x 'Ashworth', 'Ashworth' x open seed.  The pollen source for the crosses is the staminate flower on 'Ashworth.'  He is now evaluating the pod quality and yield of these crosses.


Cottingham writes, "Right now, my best idea for a [honeylocust] planting would be planting seeds of ('Calhoun' x male or perfect 'Calhoun x Ashworth') planted like walnuts -- several seeds at each spot.  Then graft the best to the worst, hopefully having perfect flowered pollinators with good fruit throughout.  'Hershey' probably is as good or better than 'Calhoun.'  A minimum of eight years would be required for significant production if extensive grafting is required." (Jerry Cottingham, Box 251, Medina, TX 78055 USA)


Projects with Agroforestry Honeylocust


Since the last newsletter, a number of new agroforestry honeylocust projects have begun.  In addition to the following, projects have been initiated in Belgium, Greece, Germany, and the United Kingdom.  I will report on these and others in the next newsletter. 


McRae Trust Farm in New Zealand has an ll year old honeylocust orchard of 80 trees.  Grafted trees were planted to test 14 cultivars under "fairly harsh conditions."  Trees are planted on 10 meter squares and will be thinned based on pasture deterioration.  The trees are protected with electric system which will eventually be removed to see if the trees can survive without it.  Trees began fruiting at age 6 and pod production is being monitored.  Major anticipated benefits include the favorable pasture microclimate providing light shelter and easing stress on livestock and grass. (J.R.deZ.Hall, 383 Palmerston Road, P.O. Box 445, Gisborne, New Zealand)


Robert Lance has an 8 year old honeylocust orchard to test 4 cultivars ('Millwood,' 'Calhoun' and two local selections) on his farm in Australia.  Trees are planted at 100 trees/hectare in pastures and trickle irrigation is used good growth.  Lance has a 4 hectare paddock where he plans to accumulate a range of promising selections. (Robert Lance, Stillwater, RMS 3310, Yarra via Goulburn N.S.W. 2580 Australia)


Arbor Day Foundation is experimenting with thornless honeylocust, hybrid poplar (3 cultivars), and silver maple as biomass energy inputs for the fuelwood plant (heating, cooling, and hot water) at the Foundation's Conference Center.  Trees will be harvested by coppicing in a 5-7 year cycle. (Chris Aden, Arbor Day Farm, 2700 Sylvan Road, Nebraska City NE 68410 USA)


The Department of Forestry at Virginia Tech University, in collaboration with the Agricultural Research Service-USDA and Springtree Agroforestry Project, has begun 2 honeylocust plantings: one hectare of seedling honeylocust will be used to test understory light and grass interactions; one hectare will specifically test grafted 'Millwood' honeylocust.  Both plantings will include several spacing and tree protection replications, control plots, and will be grazed by sheep.  These plantings are part of a larger agroforestry project at the University's Whitehorne Research Farm in Blacksburg, Virginia.


Trees for Life and Springtree Agroforestry Project have begun honeylocust introductory trials at 5 sites in India.  Seedlings growing at the sites will be transplanted to pastures and hedgerows this spring. (Bilbir Mathur, 1103 Jefferson, Wichita, Kansas 67203 USA)


Page 4

Honeylocust Leaf and Twig Fodder

Three groups are experimenting with honeylocust leaves and twigs for livestock fodder.  Leaf fodder may be used on a cut-and-carry basis or browsed directly by livestock, usually sheep or goats.  I believe honeylocust leaf fodder as part of an alley crop system (interplanted with other fodder species) has great potential for economically developing countries.


Heifer Project International has a 10-year alley crop demonstration where honeylocust (inermis) are interplanted with black locust, mimosa, and alders.  The trees are lopped at 1 meter several times each year and leaf fodder is fed to goats on a cut-and-carry basis.  Trees are spaced 9 cm within rows and 8 meters between rows on the contour of 1/4 hectare hilltop.  The alley crop project is part of the organization's sustainable agriculture visitor center.  In 1995 The Heifer Project began a silvopastural demonstration with 'Millwood' honeylocust planted in a working sheep pasture. (Chuck Crimmins, Rt. 2 Box 33, Perryville, AR 72206 USA)


North Carolina State University Master of Science candidate Ben Addleston is testing honeylocust, black locust, and mimosa as directly grazed protein supplements for goats.  The study will measure differences in biomass between the 3 species at interrow densities of 1 and 0.5 meters, and cutting heights of 25 and 50 cm.  The objective of the study, started in 1995, is to provide a more dependable source of protein for livestock in hotter months when typical forages are not as productive and nutritious, especially in times of severe drought. (School of Forestry, Raleigh, NC 27600 USA).


The Bio-Integral Resource Center (BIRC) plans to use staminate (male) honeylocust in pasture plantings to provide leaf and twig fodder for sheep on a cut-and-carry basis.  Browse would be fed in the summer when pasture is dry and low in nitrogen.  BIRC has planted seedling and grafted honeylocust along berms and fencelines in their sheep pastures.  This planting will ultimately provide estimates of honeylocust pod production in the semi-arid environment of the northern California foothills.  Trees are drip irrigated and protected by fences and wire cages. (Shawn King, BRIC, 3524 Digger Pine Ridge, Winters, CA 95694 USA.)


See: 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. Jr. Animal Science. 63:2028-2043.


Windy Slope Farm, with assistance from Springtree Agroforestry Project, has established 5 honeylocust cultivars in sheep and cow pastures.  Trees are spaced 10 meters, and are protected from deer and livestock browsing by existing electric fences. (John Fichtner, Rt. 1, Leroy, WV 25252 USA)

Page 5                                              Honeylocust Beer


Yes, last year our brau frau, Ruth Klippstein, used 14 pounds of pods to brew up 4 gallons of honeylocust beer and it was quite tasty.  Aged a year, it has a warm golden color, a spicy, earthy bouquet, and a scattering of effervescence--not a real head.  The test is more reminiscent of alcoholic cider than a lager beer, but this recipe stands firmly in the tradition of country brews ranging from spruce beer to elderflower champagne.  Write us for the receipt and watch for forthcoming reports of honeylocust-persimmon beer which we plan to try this year!                  




The Honeylocust Research Group(HRG) was organized to facilitate communication between researchers working with honeylocust agroforestry.  The HRG Newsletter  provides a place to share preliminary findings, pre-publication material, and answers to questions on honeylocust.  There are now researchers working with honeylocust in 10 countries.  Since the last newsletter a number of innovative projects have been initiated.  Preliminary findings of symbiotic nitrogen fixation in honeylocust roots will undoubtedly stimulate additional interest.  If you are presently working with honeylocust, we urge you to continue.  The cumulative information from honeylocust plantings in different environments will make more meaningful the results from individual projects.  Send me a note on how your project is going, your results to date, and what problems you have encountered.


Grafted Honeylocust Available


Grafted honeyloucst are available from Hidden Springs Nursery, Rt. 14 Box 159, Cookeville, TN 38501 USA.  Honeylocust seed from 'Millwood' x open seed is available from Springtree Agroforestry Project.  Many commercial nurseries in the US sell honeylocust seedlings; however, these seedlings are from northern seed sources which are potentially incompatible with cultivars from the southern US. 


HRG NEWSLETTER is written by Andy Wilson and produced by the Springtree Agroforestry Project at Springtree Community(Ruth Klippstein, Evelyn Edson, Tom Klippstein, and Andy Wilson), 268 Springtree Lane, Scottsville, VA 24590 USA. Phone: 434-286-3466, Fax: 434-971-8232  e-mail awilson@pvcc.edu.   Thanks to those who have sent money to help support HRG NEWSLETTER.  Financial contributions to cover costs of printing and mailing are gratefully accepted.