In Search of the Wild Ban Li . Added to the TACF listerv September 2008

We were privileged to be members of TACF's mission to China in September, 2008. Our objectives were:

1) to seek collaboration in planting and testing of TACF backcross trees in China;

2) to observe the fungus in its native environment; and

3) to document the basic ecology of wild Chinese chestnut populations.

We hoped to learn how Castanea mollissima fares in its native environment --in the forests of China, not its orchards. We wondered whether Chinese chestnut is damaged enough by blight to not grow well. We also wanted to see whether there was any evidence of blight resistance "breaking down," where some trees would be severely disfigured by blight. Finally, by growing TACF backcross trees in China, we might determine whether their resistance could "break down" when exposed to the full array of native strains of the blight fungus.

There are three species of chestnut native to China, C. mollissima, which we all know as Chinese chestnut, as well as C. henryi and C. seguinii. In Chinese, C. mollissima is called "ban li" while C. henryi is called "zhui li," and C. seguinii called "mao li."

TACF's first president, Phil Rutter, visited Hubei Province in 1989 to try to observe and collect seed from wild ban li. With the help of Hongwen Huong, then of the Wuhan Botanical Institute in Hubei, Phil was able to collect some seed from ban li that, if not wild, were at least escaped from cultivation. Their expedition, however, could not penetrate very far into the mountains, which were much more inaccessible in those days, and Phil was never sure that the ban li seed he collected came from truly wild trees.

Phil and Hongwen collected seed from both ban li and mao li, and some were grown at TACF's Meadowview Research Farms. Yan Shi tested these for blight resistance in 1996. Some of the ban li seedlings tested as having good blight resistance, and have been advanced, to date, as far as second backcross to American chestnut. However, none of the mao li tested as having good resistance.

Our first destination, Da Lao Ling Forest Park, was also in Hubei Province, but further west, about 25 kilometers northwest of the Three Gorges Dam on the Yangtze River. However, it was high in the Da Lao Ling Mountains, reaching elevations above 2000 meters, almost 7000 feet. So we were penetrating much farther into the mountains than Phil and Hongwen and had high hopes of seeing wild ban li.

The Da Lao Ling Forest Park was created to help protect the flora and fauna of the magnificent Three Gorges region, some of the most diverse in China. The mountains in this part of China, as in many others, are very steep. Despite the steepness, people farm high into the mountains, terracing the land, on slopes well over 20%. However, when the slopes finally reach the neighborhood of 75-100%, even terracing is impossible and cultivation ceases. It is on these exceedingly high, steep slopes where native forests persist, relatively undisturbed by cultivation, although most sites may have been cutover at least once. And the native forests were where we hoped to find the wild ban li.

After arriving in Da Lao Ling, we proceeded to two sites identified by Dr. Yehao Shen, of Peking University, as the most likely to contain wild chestnut. At the first site, along a stream whose name translates as Hog Trough Creek, we saw numerous zhui li, and a few ban li. At the second site, zhui li and mao li. So things were promising. The next morning, we examined the first site more carefully and in the afternoon hiked up a narrow gorge to Dr. Yehao's permanent research plot, perhaps 600 to 700 feet above Hog Trough Creek. Here, things got more confusing as we measured a chestnut that keyed out as a mao li yet was 87 feet tall and 17.5 inches in diameter and with a straight bole clear of branches to a considerable height. Since mao li is described as a shrub, rarely exceeding 40 feet tall, at least one of us, Hebard, was thoroughly confused!

However, Dr. Yehao also had seen this, and further examination confirmed mao li over 80 feet tall and zhui li over 90.

The third day in Da La Ling, we measured --on as many chestnut as possible-- the height, diameter, form, health, fraction of blighted "cankered" stem, canker severity and presence of seedlings. Again, the large sizes of mao li and zhui li were confirmed. Unfortunately, at the few locations with ban li, we could not unequivocally determine that the trees were indeed wild, rather than planted or naturalized, having escaped from cultivation.

After a fourth day in Da Lao Ling, we departed by train for Ankang, in Shanxi Province. On arrival in Ankang, we went to visit some cultivated ban li and were shown ban li referred to as wild mixed among them. But here, it was clearly impossible to rule out planting or escape from cultivation, and we were quite despondent at the end of our first day in Ankang: the promise of seeing wild ban li seemed to be fading.

The next morning, we drove up to a village above the town of Zan Gao, where 50-foot-tall ban li and zhui li were being harvested for poles and firewood. Our principle guide in Ankang, Mr. Chen Yuchen, a forester who researched the distribution of ban li in China also referred to these trees as wild. However, their proximity to orchard ban li again made it difficult to confirm they were wild. Hope of viewing wild ban li seemed lost.

But then, as we traveled higher into the mountains to Nan Gongshan National Forest Park, the road cut across a slope of 100%, barely climbable, rising out of a boulder-strewn creek with no flood plain. And some large chestnut were present that did not appear to be zhui li. But were they ban li or mao li? Climbing down, they clearly were ban li, with simple and stellate hairs on the underside of the leaf, between the veins, as well as tan-colored twigs and three plumpish nuts hairy only on top. On our final full day in the field, the wild, forest-grown ban li at last!

These trees measured up to 62 feet tall and 13 inches in diameter. All were clearly cankered, although we had only seen stroma of the blight fungus on one ban li back in Da Lao Ling. Even though Nan Gongshan is a national park it is clear that this part of the forest had been harvested at some time in the not too distant past. So the size of the trees is not indicative of "old growth" ban-li. According to Mr. Chen, they sometimes grow much larger than those we saw.

On further questioning, Mr. Chen acknowledged the distinction between wild and naturalized, which is not made in Chinese forest science. His experience indicated to him that the so-called wild trees he had shown us the first day quite possibly were naturalized, and also that the ban li in the higher reaches of Nan Gongshan were wild.

So we observed ban li, or Chinese chestnut, with cankering similar to that seen in the United States, but not more severe. Thus blight resistance does not appear to be "breaking down" on wild ban li. Interestingly, Mr Chen and other Chinese experts rated ban li as least resistant, then mao li, and zhui li as most resistant. These two species may provide additional sources of blight resistance going into the future. In the meantime, if TACF has indeed transferred blight resistance from ban li to our third-backcross, F3 seedlings, blight should not overly hamper their ability to grow in our American woodlands.

Some pictures and Blog at:

--Fred Hebard, Sara Fitzsimmons, Songlin Fei, Fred Paillet, and Kim Steiner