Fall 2025 has proven to be a lucky season so far as we are in midst of the still unexplained ecological phenomena of an Oak Mast Year. Somehow Oak trees across the North Hemisphere have all collectively decided to produce an above-average, large amount of acorns this year. The last Mast Year was 2020. I have a distinctive memory of walking down West 22nd Avenue between Cambie and Ontario (a street lined with English Oaks) on a misty late September 2020 evening and the night being alive with sound of acorns dropping from trees. The corky cushiony sound of them hitting the pavement and cars and bouncing upwards again. Hopefully finding a welcoming landing on a batch of grass. Catching the eye of a woman sitting on her porch listening to the sound and us both laughing a particularly powerful gust of wind created a rain of acorns upon the streets.
The oaks have decided to bless us this year as well. There are no native oak trees to Vancouver, but non-native oaks are very popular street trees, with the English Oak and its long extended acorn being the favorite. English Oak has naturalized quite well in Pacific Spirit Park, enjoying the mild and wet winters that remind it of its homeland in Europe. Walk through Pacific Spirit Park and you will find stumbling across small English Oaks is quiet common. A lot of these small oaks look to be about five years old. Proof of the successful mast year of 2020!
Our current understanding of mast years suggests they are a gamble that oak trees make to overwhelm predators and allow more acorns to survive and grow into trees. Somehow oaks collectively decide that a certain year will be bumper crop year. Evidence suggests that it’s somewhat attached to certain types of weather – a collective experience for oaks – but the pattern has been yet to be figured out, with oak masts still yet to be successfully predicted. Being not predictable is also the whole point of a Mast! If predators like rodents – which make a lot complex survival decisions based on environmental factors – were able to predict when masts were to occur, it would defeat the purposes of the Masts. Which is to catch predators unaware and overwhelm them. Evidence suggests that Masts are purposely unpredictable and chemical signaling between oaks are big factor in making the decision.
I encourage you to do a little web searching on Oak Masts! A number of studies have come out that claim to solve the mystery but even more studies have come lately out to show it is even more complicated and confusing then we think it is.
It will be interesting to see what impact the Mast has on Pacific Spirit Park! More English Oak trees in the Park is an obvious one. English Oak is not currently considered ‘invasive’ in Pacific Spirit. Meaning it doesn’t over-dominate its habitat or damage native species. However, it’s clear that it is becoming more and more common. I wonder how soon before it crosses that line between friendly to scary? Consider Sycamore Maples, another European tree that was at first not considered invasive to the park, but now has taken over so much that is it considered dangerous. Scientists now talk of ‘sleeper species’ that don’t appear invasive at first, until their numbers get so big that a ‘tipping point’ occurs and they start spreading rapidly.
For example of some negative impacts, consider our native Douglas Squirrels, those cute red bellied squirrels, who don’t cross urban areas well and exist in Pacific Spirit as like they are on an island. Their ancestors cut off from expanding and exploring by being boxed in by the city of Vancouver, UBC, and the ocean. Douglas Squirrels survive in the Park thanks to the seeds from Douglas Firs, Big Leaf Maples, and Vine Maple. They probably can adapt and learn to eat English Oak Acorns, but likely not before invasive Eastern Grey Squirrels have followed their beloved English Oak Acorns deep into the Park.
You’ve likely seen the new signs all over the Park. That the ‘forest is changing after years of storms, heat/drought events, and insect infestations’. Trees may fall “without warning” and to be “aware of your surroundings at all times”. There will be new gaps in the canopy and open areas, areas perfectly suited this incoming mast of English Oak Acorns.
This next spring, keep your eyes on the ground for English Oaks. Are they a friend or foe? Or something else? A sign of a future forest that we don’t yet understand?
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