Woodpecker Damage on Ash Trees at the Morgan Arboretum


The emerald ash borer (EAB) has killed 75 million ash trees in North America since 2002 (“Ville de Montreal”, 2015), causing Montreal to invest 15 million dollars over the next three years to deal with the infestation, and plant new trees (Laframboise, 2016). Predators of the EAB larvae include woodpeckers (Jennings et al., 2013). As the Island of Montreal is home to multiple species of both ashes and woodpeckers, we wanted to explore the relationship between these two organisms.

Emerald Ash Borer

The emerald ash borer is an invasive species to North America accidentally brought in from Asia (Daniel & Deborah, 2013). This green beetle feeds on the sap of ash trees and lays its eggs into the tree bark crevices. It infects all ash species (Daniel & Deborah, 2013). Damaged tree stands die within 1-4 years after infestation from this pest (“Emerald ash borer”, n.d). Since the EAB has no effective predator, forests with a high number of ash trees are likely to decrease significantly in the coming years.

image-1-and-2Figure 1. Ash tree leaves on the left and ash tree bark on the right.

Ash Trees

Ash trees (Fraxinus species) are large deciduous trees that grow on moist, well-drained soil in areas with direct sunlight. They have both opposite branching and leaves, and typically have 5-9 leaflets on a branch with smooth or toothed margins (Brown-Rytlewski & Thompson, 2003). They also produce wind dispersed samaras. Ash trees are easily identified by their bark; young trees have a relatively smooth, grey bark, whereas as they mature, diamond-shaped ridges develop.

Ash trees are common in many parts of the United States and Canada. On the island of Montreal ash trees are ranked the second most numerous species, with red ash being the most common (Rocha, 2015).

image-3Figure 2. Most common species of tree in Montreal based on boroughs.

White ash trees are the predominant species of ash present in our study area, the Morgan Arboretum, a forest reserve located on the western tip of the Island of Montreal.


Woodpeckers peck at tree trunks for numerous reasons, including finding insects and building nest holes. They drum into trees to communicate, and can tap up to 8,000-12,000 times a day (Eberhardt, 1997). Woodpeckers are found in wooded areas worldwide with the exception of Australia (Helmut, 2016). They have a diversified diet with insects as their primary food source, followed by fruits, seeds, and nuts. Their bodies are designed to prevent damage to vital organs; they have powerful neck muscles and a thick skull that protects their brain and spinal cord (Spring L. W., 1965).  The woodpecker’s tongue can extend, and is often covered with sticky saliva that allows them to catch more prey. They also have a strong, slightly curved bill that facilitates exposing insects in the tree bark (Zhou et al., 2009). At the Morgan Arboretum we observed damage on ash trees from the following woodpecker species: pileated, red-bellied, sapsucker, hairy and downy. Woodpecker characteristics vary, as shown in table 1.

table-1Table 1: Characteristics of Woodpeckers Observed at the Morgan Arboretum

Factors Influencing Woodpecker Foraging Activity

Forest type, tree density and tree health each influence woodpecker activity in different respects. In fact, it has been shown that a larger diversity of woodpecker species can be found in deciduous forests than in coniferous forests (Myczko et al., 2014). Moreover, low density forests are possibly preferable for larger woodpecker species, because they lead to less hampering of movement and foraging (Myczko et al., 2014). However, the forest density also affects smaller species of woodpeckers, such as sapsuckers.  According to Lawler & Edwards (2006), sapsuckers are more likely to nest in forests of low density. That study also showed that more sapsucker nests were observed in areas with a higher presence of fallen dead trees. This preference has also been shown for downy, hairy and red-bellied woodpeckers (Lindell et al., 2008). These results confirm that tree health is a factor affecting woodpecker activity. In a study by Flower et al., it was found that in EAB infested forests, bark-foraging birds, including woodpeckers, fed more often on ash trees, and preferentially fed on ash trees with canopy decline most likely linked to the EAB (Flower et al., 2014). No research addressing the relationship between woodpecker presence and ash tree bark quality has been conducted in the Arboretum.

Our Research

EAB invasion is likely to reduce ash tree populations in the coming years. We wanted to understand the relationship between woodpeckers and ash trees before ash tree populations decrease significantly. Research by Myczko et al. (2014), and Lawler & Edwards (2006) shows that tree density influences woodpecker presence, hence we incorporated basal area as a measure of tree density into our research. We also decided to measure density of ash trees more specifically since they are affected by the EAB.

Research question: Does the density of ash trees and basal area affect the foraging activity of woodpeckers on ash trees at the Morgan Arboretum?


To carry out our experiment, we randomly selected six 50m2 sectors, and divided them each into four 25m2 plots. Two out of the four squares were randomly selected. In each plot, we measured the diameter of all standing trees at breast height (DBH) and also identified the specie of each tree, to be able to calculate basal area. Furthermore, for all of the ash trees we encountered, we used iNaturalist to record the position and number of each tree, as well as photograph the woodpecker damage whenever it was encountered. Finally, each ash tree was ranked on two scales; one based on their bark quality, and the other based on the severity of the woodpecker damage on the tree.

table-2Table 2: Scale for Bark Quality  

table-3Table 3: Scale for Woodpecker Damage

Whenever possible, we noted the most probable woodpecker species, that had caused the damage observed on the tree. The data collected will be analyzed in order to see if there is any correlation between ash tree density, basal area and woodpecker damage in the Arboretum.

Here is a video describing our data collection process.



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Jennings, D. E., Gould, J. R., Vandenberg, J. D., Duan, J. J., & Shrewsbury, P. M. (2013). Quantifying the impact of woodpecker Predation on population dynamics of the Emerald Ash borer (Agrilus planipennis). PLOS ONE, 8(12), e83491. doi:10.1371/journal.pone.0083491

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Picture References

Belhumeur, R. (n.d.). Yellow-bellied Sapsucker Adult female [Digital image]. Retrieved from https://www.allaboutbirds.org/guide/Yellow-bellied_Sapsucker/id

Hanrahan, C. (n.d.). Hairy woodpeckers (Picoides villosus) scaling bark from trees [Digital image]. Retrieved from https://fletcherwildlifegarden.wordpress.com/2013/01/21/hairy-woodpeckers-picoides-villosus-scaling-bark-from-trees/

(n.d.). Downy Woodpecker Adult male [Digital image]. Retrieved from https://www.allaboutbirds.org/guide/Downy_Woodpecker/id

Jobes, W. (n.d.). Red-bellied Woodpecker Adult male [Digital image]. Retrieved from https://www.allaboutbirds.org/guide/Red-bellied_Woodpecker/id

(n.d.). Northern Flicker Male (Red-shafted) [Digital image]. Retrieved from https://www.allaboutbirds.org/guide/Northern_Flicker/id

Northern Flicker [Digital image]. (n.d.). Retrieved from http://www.wildbirdhabitatstore.com/index.php?option=com_content&view=article&id=79:northern-flicker-2&catid=2&Itemid=195

Oyer, B. (n.d.). Hairy Woodpecker Adult male [Digital image]. Retrieved from https://www.allaboutbirds.org/guide/Hairy_Woodpecker/id

(n.d.). Just Your Average Beautiful South Florida Day [Digital image]. Retrieved from https://palmbeachcountynaturally.wordpress.com/2012/03/23/just-your-average-beautiful-south-florida-day/

Smith, M. (n.d.). Pileated Woodpecker [Digital image]. Retrieved from http://www.audubon.org/field-guide/bird/pileated-woodpecker

Sharpe, M. (n.d.). Pileated Woodpecker Adult male [Digital image]. Retrieved from https://www.allaboutbirds.org/guide/Pileated_Woodpecker/id










2 comments on “Woodpecker Damage on Ash Trees at the Morgan Arboretum

  1. I own a piece of land of some 35 acres in Rawdon, Qc, along the Red river.  In may 2015, there was a forest fire that heated the bark of my trees.  The bark got hot with the brush fire (dry autom leaves that burnt very hot). Now, the bark of many trees, most évident on the ashes, is peeling of the first 3 to 10 feet up of the trees.  Will they survive or am I better to cut them down and use the wood for firewood in my stoves ??? Thank you. Roger BeausoleilRawdon.


    | Chris Cloutier posted: “IntroductionThe emerald ash borer (EAB) has killed 75 million ash trees in North America since 2002 (“Ville de Montreal”, 2015), causing Montreal to invest 15 million dollars over the next three years to deal with the infestation, and plant new trees (L” | |

    • Hi Mr Beausoleil,

      Thank you for your comment.

      Of what we learned, bark peeling is an important indicator of decreasing tree health. The density of the foliage is also important. If your trees had a healthy foliage this summer, one year after the fire, we think they will survive. However, we are not qualified to know for sure.

      Noémie Roy, Woodpecker group

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