Two species of ash trees are critically endangered

TL;DR: Two species of trees, the green and black ash, are critically endangered. In cities and on farms across Saskatchewan and Manitoba more and more of these trees are dying because of two invasive species: the cottony ash psyllid, from Southern Europe, and the emerald ash borer, from Asia. Extreme heat and drought conditions make ash more susceptible to these pests, which means Prairie cities, like Saskatoon, have already had to cut down thousands of these trees in recent years because of infestations. 

The preamble: One Flatlander reader named Regina suggested this week’s topic. 

She wrote: I was wondering why all the green ash in southeastern Saskatchewan is showing so much dead. I noticed it in my own shelterbelt and every farm on my weekly shopping trip to Estevan or Weyburn. I think my shelterbelt will only have evergreen, chokecherry, and caraganda trees left.

I’ve been wondering the same thing myself, as I made the same observation several weeks ago while driving to Saskatoon last month.

In researching this issue, I was shocked to find out green ash is critically endangered; and so is the black ash, another common Prairie tree, according to the International Union for the Conservation of Nature’s “Red List,” the preeminent global inventory for species’ conservation status.

We don’t generally think of trees as critically endangered, but according to a recent Washington Post article, 1 in 6 U.S. tree species are endagered.

The damage: In 2018, Saskatoon had to remove 1,600 infected ash trees because of the cottony ash psyllid, also known as CAP or jumping tree lice. In 2019, the city removed another 2,900 trees, and then  another 800 in 2020. These measures took out approximately half of the black ash trees in Saskatoon.

In 2017, the City of Winnipeg noticed an infestation of jumping tree lice in the trees around The Forks. In 2018, 700 ash trees in Winnipeg, mostly in the Riverview and River Heights area, had to be chopped down because of lice. City staff say evidence of the insect has since been found in varying degrees throughout the city. 

Also in 2017, the Emerald ash borer (EAB) larvae were found in a tree in Winnipeg’s St. Boniface neighbourhood. Since then, the city has been working hard to keep this bug under control ever since, as once the bug takes hold, they can decimate a population of trees within 10 years.

If you see ash trees in Winnipeg with a bunch of large syringes at the base of the tree, they are being injected with TreeAzin or IMA-jet, solutions meant to kill ash-borer larvae. These “vaccinations” last for about two years, and then it is time for another shot. 

Despite Winnipeg’s best efforts, these two pests, CAP and EAD, led to Winnipeg chopping down 12,000 ash trees in 2019. 

Winnipeg has about 14,400 black and Manchurian ash trees. It also has 350,000 green ash trees, which comprise close to one-third of the urban forest canopy. If these bugs get the opportunity, they could spread with a vengeance and destroy a significant section of the city’s canopy of trees.

Heat and drought makes the damage worse 

Trees stressed by extreme weather are weakened, because if they aren’t well hydrated, they aren’t able to produce enough resin, the sticky substance they use to seal up wounds and trap insects.

Pests aside, drought alone can kill trees. In 2020, Regina had a net loss of 356 trees. According to a city report, many trees died because of extended drought. In 2021, another 519 trees had to be removed. 

Extreme storms also take down trees on their own. In 2020, sixty-three trees were removed because of damage. 

The good news:

• The Manchurian ash found in Saskatchewan and Manitoba isn’t currently endangered. It is listed as a species of least concern, for now. 
• EAD hasn’t spread to Saskatchewan yet, but the province is actively monitoring for it. 
• And there are things you can actively do to help.

Read more:

• I know nothing about trees. Do I even have an ash tree in my yard?
• How do I know if I have CAP in my ash trees?
• What can I do to protect my ash trees from CAP?
• How do I know if I have EAB in my ash trees?
• What we can all do to prevent a tree apocalypse

I know nothing about trees. Do I even have an ash tree in my yard?

Here are some images and descriptions of the different types of ash trees found on the Prairies that are affected by these pests.

Green ash:

• The leaves are medium to dark green, but turn bright yellow in the fall.
• The leaves are six to nine inches in length. 
• There are about five to nine leaflets on the stalk to the petiole  (the stalk that joins a leaf to a stem).
• In the spring, the trees produce a reddish-purple flower.
• The green ash also produces these elongated samaras that are about an inch or two long. Samaras are a type of fruit, which some people call ash keys. Apparently some people pickle and eat them.
• These trees grow between 12 and 25 metres high.
• Their trunk diameter can get as big as 60 centimetres.

Black ash:

• The leaves are dark green and turn yellow in the fall
• The leaves are nine to 16 inches long 
• There are seven to 13 oval to lance-elliptic leaflets. 
• These trees grow between 15 and 20 metres high.
• They produce purplish flowers that grow in compact clusters.
• Their trunk diameter can get as big as 60 centimetres, although some have been found with trunks as big as 160 cm. 
• The green ash also produces oval shaped samaras

Manchurian ash:

• The leaves are a dark green that turn golden-yellow in the fall.
• Trees reach 30 metres tall with a trunk up to 50 cm in diameter 
• The leaves are 25 to 40 cm long
• There are seven to 13 leaflets
• It produces greenish yellow flowers in the spring
• It produces oval samara, also known as ash wings.

How do I know if I have CAP in my ash trees?

They are hard to see. CAP are very small. The biggest ones are about four mm. The bugs are also light green or yellow green. 

It’s easier to spot them because of the damage they cause. 

• If you have white cotton curled within or along the leaves. You have tree lice.
• Heavily infested trees will often be partially defoliated with some of the remaining leaves twisted into a corkscrew or cauliflower shape.

What can I do to protect my ash trees from CAP?

The most effective deterrent seems to be keeping the trees well-watered and stress free. Pruning and mulching also help. When in doubt, call an arborist. 

How do I know if I have EAB in my ash trees?

• Larvae leave a distinct ‘s’ shape marking in the wood as they eat
• The tree may develop sprouts (epicormic shoots) from the roots, trunk or branches in an effort to find new ways to transport nutrients. 
• Signs of EAB infestation become the most obvious when the leaves lose their green colour and there is a thinning of the crown of the tree.

The most tree damage is caused by the EAB larvae, which destroy the layer under the bark (the cambium) that is responsible for transporting nutrients and water throughout the tree. Basically, they starve the tree to death.

This will kill a healthy tree in two to five years depending on the age and the extent of infestation.

If you think your tree has EAB, you should call the national Emerald Ash Borer hotline at 1-866-463-6017.

What we can all do to prevent a tree apocalypse

Plant a variety of trees in your yard.

The problem with prairie cities, like Winnipeg is they planted a monoculture first by planting mostly elm trees, and when those were hit hard with Dutch Elm Disease, they created a second monoculture, by replacing those trees with mostly ash trees. This was fine until EAB and CAP arrived in the early 2000s. 

Pests, like EAB, fly from tree to tree, but they can only fly so far, so if the next trees over are a maple or a poplar tree, the bugs won’t be able to feed and die off. 

Don’t move firewood around

It is illegal to take ash or any type of firewood outside or inside of city limits under federal regulations. You also aren’t allowed to transport firewood between provinces.

It’s actually recommended that people not even move firewood or wood around at all, even within city limits, to help control the spread of pests.  

The experts say you should burn the wood where you collect it or buy it, unless it is heat-treated (kiln-dried) wood that ensures all the pests are dead.

I just picked up some kiln-dried wood from my local hardware store recently, so it’s pretty easy to find.