For many years, the six American elm clones which comprise the "American Liberty" series have been a source of controversy and confusion for those who have sought to restore stands of American elm through planting of DED-tolerant strains of the species. Quite simply, the information necessary to evaluate the merits of the six Liberty clones has been partially or entirely unavailable to the public, for complex reasons, which is why I was forced to discover what I could through independent research. Moreover, the sudden availability of newly released American elm cultivars in the 1990's led to considerable rivalry and competitiveness, or so it appeared constantly in the media, a fact which did not help to clarify anything and which many people found tiresome. My early speculations about the Liberty elms were based solely on technical disclosures sent to me by researchers at the University of Wisconsin, and I purposely took with a grain of salt all unsubstantiated criticism of the trees, as I was seeking unbiased information and did not want to be influenced by anyone who might be a competitor to those researchers in any way. In more recent years, I was able to make some field observations which unfortunately have strained my regard for the best of the Liberty clones and have led me to post a Liberty elm warning of my own. Nonetheless, the factual disclosures from which I had formed my earlier speculations remain available in the paragraphs below, in case they may be of interest.
In a letter to me in 1993, a member of the University of Wisconsin research team which developed the six American Liberty clones told me in response to a query, "Among American elms, 'American Liberty elm' is probably as resistant as any American elm we have evaluated. Several others are comparable, but we see little point in pushing these onto the market if better ones might be available soon." In that same letter, this individual also said, "Our general observation is that 'American Liberty elm' does not succumb to Dutch elm disease when planted at a low density; however, we do not recommend creating large urban monocultures of this clone, or any species for that matter, to avoid the possibility of future epidemics."
At my request, that individual enclosed some technical information, including a reprint of a publication summarizing the results of experiments on the Liberty elms performed in a field setting in the 1970s, and again in a greenhouse in 1990. I have not been able to find that research report on the internet. The field results from the 1970s are displayed largely out of context in connection with the patent on the Independence clone. The results of the 1990 greenhouse testing in the above-mentioned report suggest that the six American Liberty clones are highly resistant to "less aggressive" strains of the Dutch elm disease fungus (i.e. the original Ophiostoma ulmi), in dramatic contrast to susceptible controls, making them at least "clearly greatly improved over non-selected, wild American elms." When inoculated with the "aggressive strain" (O. novo-ulmi) which commonly goes around in nature nowadays, according to the report, the six clones showed (much like the English elm) considerably more susceptibility, but varying widely in degree among individual clones, ranging from seemingly questionable resistance to seemingly moderate resistance in the case of two clones: W-510 (or "Independence"), and an unnamed clone designated as W-502.
In a further correspondance, another of the researchers who wrote that same report (the late Dr. Eugene Smalley) urged caution in drawing conclusions too readily from any such test in a controlled greenhouse environment, as it cannot be compared directly with what happens in a natural setting; but he indicated, at least, that when planted in a natural setting, "all of the American Liberty clones have improved survival, whereas individuals from the general elm populations die."
Calling the American Liberty clones "worthy candidates for release and public trial" because of the "long time survival and mature plant resistance" of various parent plants, the authors of that 1993 report "postulate that vigorously growing ramets which are not infected during the first few years of growth will generally not become infected in later years after reaching maturity. Parents of the 'American Liberty' elms have survived for many years in situations of severe disease and bark beetle pressure. The oldest of the surviving parents is now more than 35 years old and at this time remains healthy and disease free."
The above-mentioned report is titled, American Liberty Elms and Beyond: Going from the Impossible to the Difficult. Its authors are E. B. Smalley, R. P. Guries, and D. T. Lester. That report is the fourth chapter of a 1993 scientific publication titled, Dutch Elm Disease Research: Cellular and Molecular Approaches, edited by Mariam B. Sticklen and James L. Sherald. (Springer-Verlag, New York, NY.)
In 1996, I also wrote to one of the USDA research geneticists who gave us the Valley Forge and New Harmony elms. In his response to my queries, he informed me that while the American Liberty elms had performed poorly in the USDA experiment of 1992-93, I should "keep in mind that the inoculation procedure used was very severe (not natural) and that 'American Liberty' is six different clones." He enclosed, at my request, a technical reprint from 1995, which is now posted here with permision, as is a subsequent report on a seven-year study. It is clear from these two reports that the six American Liberty clones had been treated (by necessity) as a single collective entity in the USDA experiments and had not been identified and tested separately, as would have been preferable. It seems noteworthy also that certain other clones (e.g. 'Delaware') which had performed well in earlier experiments appear to have performed relatively poorly when suddenly subjected, like the Liberty elms, to these more severe testing procedures.
The bottom line, of course, is that only the consistent performance of trees in natural plantings over the years will show how accurate any claims about any of the available American elm varieties actually are. My own field observations of Liberty elms since 2006 have shed further light on these clones which unfortunately has not been encouraging.
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American Liberty Clone Identification (added August 1, 2005)
The question of which American Liberty clone is which may be somewhat moot, in view of the questionable nature of these clones; however, the six clones in the American Liberty series can be differentiated and identified without too much difficulty if one is willing to look closely at subtle characteristics repeatedly over the course of the seasons. The information necessary to identify the particular clones has remained largely unavailable to the general public, for what reason I can only imagine; however, I do have access to some publications and notes by the late Dr. Eugene Smalley concerning this topic and thought it might be well to make some key pieces of information available through this website.
I know that I have been working with five different Liberty clones because each is consistently distinct from the others in one specific trait or another. From Dr. Smalley's notes, which include measurements of mature petiole length that vary widely among the different Liberty clones, I also know which of the six clones (W-503) is missing among those which I have been cultivating, and having seen the data on his 1990 screening tests, I even have some idea of a possible reason why that particular clone was never sent to me. Based on Smalley's descriptions and recorded measurements combined with my consistent observations and measurements over many years, I have devised the following key, which in my estimation should be generally workable for most people in distinguishing the particular American Liberty clones in their possession:
I. mature petioles (leaf stems) always shorter than 7 mm
A. leaf tips often shortened, creating relatively oval-shaped leaves .......... M-8
B. leaf tips always elongated, typical of the species .............................. W-503
II. mature petioles (leaf stems) usually between 7 mm and 11 mm
A. newly emerged spring stems completely hairless; mature leaves
large, typically around 15-17 cm long, 7-10 cm wide ........................ W-507
B. newly emerged spring stems moderately hairy; mature leaves small,
usually under 14 cm long, 7.5 cm wide; petioles long ....................... W-505
C. newly emerged spring stems profusely hairy; mature leaves large,
typically around 15-17 cm long, 7-10 cm wide
1. hairs on vigorous greenwood stems often rough to the touch ....... W-510
2. hairs on vigorous greenwood stems always soft to the touch ....... W-502
If the above key is occasionally inadequate for distinguishing clone W-502 from W-510, it may be well to note that cuttings of W-502 often shed all or most of their leaves after a few weeks when properly set as though for propagation, thus reducing considerably the eventual count of rooted cuttings, whereas cuttings of W-510 root extraordinarily easily and rapidly without shedding more than perhaps an occasional leaf. (Disclaimer: If that deplorable patent on clone W-510 is still in effect, any cuttings of that clone should be used only for decoration so the sky will not fall.) A few additional clues may be worth noting as well: Three of the Liberty clones (W-502, W-507, and W-510) occasionally produce a rudimentary leaflet at the base of a leaf on a vigorously growing shoot, whereas the other three clones are not noted for that habit. In the case of W-510, such leaflets often become large enough to create almost a compound leaf, appearing as though two leaves of nearly equal size are sharing a common petiole if not part of the leaf area, and one never finds that peculiarity occurring on W-502. Also, most Liberty clones grow vertically and become shapely more or less on their own, but W-507 has a strongly recurved and weeping habit in its early years, necessitating intensive staking.
For some reason, clone W-502 is represented among my Liberty elms many more times than all the other Liberty clones put together, so I cannot but wonder if ERI may have been emphasizing this clone in its small-scale shipments to the general public, though the patent covers a different one. After all, Dr. Smalley's published report of 1993 (referenced elsewhere on this page) suggests that W-502 has a solid pedigree and much merit in terms of DED-tolerance, in contrast to other clones, and that it therefore may deserve more consideration than it generally has been given in recent years. It perhaps should be noted that the male parent of this clone, R18-2, has performed outstandingly in a number of USDA screenings. With the available data on W-502 as scanty and inconclusive as it is, and with this clone already established in the community in considerable numbers, one would think that its merit would be investigated thoroughly and its presence acknowledged, regardless of the behavior of other clones.