An Insidious New Disease to contend with

 The natural world is having to deal with a relatively new and serious disease. It is known as Beech Leaf Disease (Litylenchus crenatae ssp. mccannii).

Beech Leaf Disease (BLD) was first noted in North America in 2012, in Lake County, Ohio, right across Lake Erie from Chatham-Kent. It has gradually spread through other jurisdictions, and as of late 2019, is now confirmed in New York, Pennsylvania and Connecticut on the US side of the lake. It was only a matter of time before it was also discovered in southwestern Ontario.

There are eight municipalities in Ontario, from Chatham-Kent in the west, to Niagara in the east and up to Toronto, where as of late 2019 BLD had been found. The key characteristics are dark, almost black areas in between the leaf veins.....

 

....in addition some of the leaves may appear partially shrivelled.

I first heard about BLD about a month ago, in late September, from a keen forest specialist: Gerry Waldron. Gerry wrote an invaluable book on Trees of the Carolinian Forest several years ago. To give Gerry his due, he is the only person who has discovered three new tree species for Canada in his career! Gerry wrote to me, advising me to be on the lookout for BLD. Shortly after checking out some of the characteristics to be looking for, I immediately thought the American Beech (AMBE) trees of Rondeau warranted a close look. For the last 3 years, I had noted Rondeau's beech trees exhibiting severe stress, even becoming partly or almost completely defoliated in mid summer. I thought that it was primarily due to the high water levels that Rondeau has been subject to. AMBE is largely an upland species, meaning they like to grow in a spot where there is good drainage. They don't like to have 'wet feet', at least not for long. They can do alright on the higher ridges of the Rondeau sandspit, and there are some decent sized ones there, indicating that they have been able to tolerate the changing water levels for many decades. However the consistent record high water levels of the last three years have caused major stress to many upland loving tree species at Rondeau.

I immediately started checking the AMBE along many of the trails at Rondeau, and over a period of several days, was quite concerned. I checked the north end of Rondeau Road and the south end of Rondeau Road (now the west side of South Point Trail). I checked the Tuliptree Trail, the Gardiner Deer Exclosure, the southeast corner of the east side of the South Point Trail, and the section of Harrison Trail between Gardiner Ave and Bennett Ave, including the Group Campground. I found evidence of BLD on virtually every AMBE tree I checked. In fact of the one hundred or more AMBE trees I was able to see clearly, there was at least some evidence of BLD on every one. There was a very small number of trees where I didn't see any evidence of BLD, but that was only because most of the leaves were either already off the tree, or they were too high up and obscured by the foliage of other nearby species.

It was easy to conclude that BLD is well established in Rondeau, and an unaffected tree would be a rarity. Here are some of the leaves I photographed at various parts of the park, which depict BLD.

South Point Trail (West)

Tuliptree Trail

Rondeau Road north

I contacted several people within the Ontario Ministry of Natural Resources & Forestry about BLD, and got some more detailed background information. A publication dated in the spring of 2020 indicated that there were only two confirmed locations for BLD in Chatham-Kent: Clear Creek Forest Provincial Park, and Sinclair's Bush, about half way between Rondeau and Blenheim. I sent several representative photos to them, and had BLD confirmed. So the abundance of BLD at Rondeau was new information. 

I checked a few other places that I had easy access to, and where AMBE were known, including:

-Clear Creek Forest Prov Park

-a woodland area along the road that crosses Morpeth Creek

-Sinclair's Bush

-McKerrall Woods, a few km northeast of Chatham

-Paxton's Bush, at the north side of Chatham, and

-a privately owned woodlot along the roadside between Ridgetown and Thamesville

I found evidence of BLD at Clear Creek and Sinclair's Bush, not surprisingly, as well as McKerrall Woods and some inconclusive evidence at the private woodlot between Ridgetown and Thamesville.

Clear Creek Forest Prov Park

McKerrall Woods

Sinclair's Bush

 There are lots of other woodlots harbouring AMBE, but it is getting almost too late in the season for satisfactory checking. A Forestry Health Specialist will be visiting some of these woodlots to collect samples of the leaves and twigs. While the symptoms are fairly apparent, forestry specialists want samples to check, to see if the nematodes that transmit the disease are present.

What does this mean for Rondeau and other woodlands where AMBE is an important component of the forest? It is hard to say for certain at this point. Some trees will likely succumb. However according to some of the persons who have been examining BLD and its affects, some trees show some resistance to the worst outcome.

At Rondeau, the American Beech-Sugar Maple forest type covers a major part of the park. There are other species in that forest type, including Basswood, Black Cherry, Tuliptree, Green Ash and various others. But for one of the main components to become potentially a very minor part, does not bode well. One particular concern is for an endangered bird species, the Acadian Flycatcher. It nests almost solely in the outer branches of AMBE.

Acadian Flycatcher nest in AMBE

For anyone familiar with Clear Creek Forest Provincial Park, you might remember that huge American Beech tree along the main trail. It was one of the largest, if not the largest, of its kind in Ontario. But it showed stress about 4 years ago and died and blew down about two years ago. Interestingly, a small AMBE right beside that massive tree was where I found evidence of BLD just a few weeks ago. It makes me wonder if BLD had some influence on the health, and subsequent death, of that huge tree.

This first image shows the huge AMBE tree in late 2011.

This is what the tree looked like in the spring of 2019, shortly after it blew down.

This next photo was taken just a couple of weeks ago, and the small AMBE in the lower left side of the photo is where I found some leaves showing BLD.

 Over the last several decades, trees like American Chestnut, American Elm and most ash species which at one time were dominant elements of southern Ontario forests, have been severely reduced. The American Chestnut is officially an endangered species. Let's hope that the American Beech does not follow that trend.

No doubt there are many more trees in various woodlots yet to be discovered, unfortunately. Please be aware of this unfortunate situation. I fully expect to be on the lookout for this next season!