More American chestnuts than thought, not enough to fight decline: study

University of Guelph researchers studied American chestnut populations in southwestern Ontario and found more than 700 trees - more than they expected - but they are not reproducing fast enough to stop decline.
Stephen Van Drunen (right) stands near an American chestnut tree with his fellow researcher Kerry Schutten. (Courtesy of Stephen Van Drunen)

There are more American chestnut trees in Ontario than researchers expected to find, but the number of new trees is not large enough to stop the decline of the species, University of Guelph researchers say.

They conducted a tree survey that looked at changes in the American chestnut population since the last survey in 2001-2002.  The results of the most recent survey will appear in the Sept. 15 edition of the journal Forest Ecology and Management, but has been published online.

"We have a fair number of large trees, but they're not reproducing enough to counteract the rate at which they're dying," Stephen Van Drunen, the lead researcher of the project, told CBC News.

The survey looked at survival rates of trees, reproduction, tree size and disease symptoms.

Van Drunen said a fungal disease, chestnut blight, which caused a significant decline in American chestnut numbers in the last century continues to affect chestnuts in North America.

Mates required

They found 781 trees in the most recent survey and Van Drunen said roughly 80 per cent were alive.

Aside from the blight killing trees before they are old enough to reproduce, he says another cause of low reproductive rates is solitary, isolated trees.

"If you have a single reproductive tree and no other chestnuts near it, it will never produce a viable seed because it needs a second tree to pollinate it," he said.

The Canadian Chestnut Council has been running a breeding program since 2001 to produce blight-resistant American chestnuts to replace those that have died from the disease.

The program introduces genes from foreign sources into Canadian chestnut trees, with a goal of eventually producing a set of blight resistant trees.

The council's science committee director, Tom Whelacky, said the first generation crossings took six years to grow and test for resistance.

"We just started testing the second set of crossings that should have some of the resistance genes in them," he said.

He says progress is slow because there are not a lot of Canadian chestnut trees in Ontario, unlike similar programs running out of Virginia and Connecticut that have thousands of trees to work with.

Benefit of chestnut revival

Van Drunen said re-introducing the trees will have an effect on the ecosystem. For example, the chestnut produces nuts every year, an important food source for forest animals.

"By reintroducing chestnuts, they would have less variability in the [amount of] food available to them, which could have implications for food webs and population structure and things like that," he said.

He says forests can adapt to the re-introduction of new chestnut trees because they have previously survived similar ecosystem disruptions.

"There certainly has been large scale changes in forest composition after chestnut largely died out. It was replaced by a lot of oaks and maples and other things," Van Drunen explained.