November 01, 2019

Three unexpected effects climate change has on our trees

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In 2015, the City of Melbourne created individual email addresses for over 70,000 city trees. Their intention was that citizens could report any issues or concerns about a specific tree.

Surprisingly (or not so surprisingly) admirers filled up the inboxes with compliments, poems, puns and even sincere love letters. While this is a comical and heartwarming reaction to an administrative experiment, it also taps into something many of us can understand: we all care about trees.

I feel we probably all have a tree or two we could write a love letter to. For me, my love letter would be to the infamous “halfway tree” between Brandon and Winnipeg or the giant elm outside my front door.

Most of us take trees for granted because they are an ever-present fixture in our daily lives, seemingly able to withstand almost anything. However, if you were in Winnipeg over the recent thanksgiving long weekend, you would have been reminded about just how fragile trees actually are.

During and after two days of unprecedented snowfall across Manitoba, trees, still bearing their leaves, snapped under the weight of the snow. According to CBC, “the city estimates about 30,000 public trees were damaged or destroyed in the unseasonable snowstorm.”

Climate change has and will bring even more hardship to our urban trees and our treasured forests. In the past decade, we have all witnessed the unprecedented forest fires and insect infestation, so I won’t repeat that coverage. Still, I have collected a few articles, which shine equally concerning light on the relationship between trees and climate change.

Can Humans Help Trees Outrun Climate Change? (New York Times)

We know our climate is changing, and we know we have to adapt to more extreme weather conditions. However, trees are not equipped to adapt to rapidly changing conditions.

As Moises Velasquez-Manoff for the New York Times explains, “most trees can migrate only as fast as their seeds disperse — and if current warming trends hold, the climate this century will change 10 times faster than many tree species can move”. The changes are occurring so fast that “species planted today may be ill-suited to conditions in 50 years, let alone 100”. 

Some researchers have experimented with the idea of “assisted migration [which] involves deliberately moving trees northward”. They aim to plant native and non-native trees, adapted for warmer and drier climates, in hopes that they will thrive in future environments.

However, some researchers also consider this a controversial idea as trees are part of a broader ecosystem, and juggling plants will have unintended consequences. As Anthony Ricciardi, a professor at the McGill School of Environment, writes, “moving species is the equivalent of ecological gambling . . . You’re spinning the roulette wheel”.

As Sea Levels Rise, So Do Ghost Forests (New York Times)

We have all heard that sea-level rise due to climate change will have a devastating impact on our coastal cities, but there’s hasn’t been very much attention paid to the effect it will have on endangered trees as well.

The rising saltwater has “[created] stands of dead trees – often bleached, sometimes blackened – known as ghost forests”. Marshes migrating inland is a natural process, but again, climate change has sped up this process to the point where the trees and plants can’t adapt quick enough.

The actual water level may only rise three to five millimetres per year. However, if the land is relatively flat like it is in Dorchester County along the Maryland coast, those five millimetres “can translate into saltwater pushing 15 feet inland per year”.

Many inland trees cannot adapt to saltwater exposure, and damage can occur rapidly. Along with the rise of the water level, increasingly intense storms have pushed saltwater further and further inland.

After Hurricane Sandy in 2012, the formation of ghost forests could be seen “along riverbanks many miles from the open ocean, suggesting that Sandy pushed seawater far up the river system”. Dr Ken Able, a professor emeritus of marine and coastal sciences at Rutgers University Marine Field Station in Tuckerton, N.J, explained bluntly “you get a slug of saltwater . . . And things die”.

Canada’s forests haven’t absorbed more carbon than they’ve released since 2001 (The Narwhal)

Trees can store carbon from the atmosphere using photosynthesis. When the tree dies, it releases this stored carbon back into the atmosphere. Forests can either be carbon sinks, where the amount of carbon stored outweighs the amount released, or carbon sources, where the amount of carbon released exceeds the amount saved.

Historically, Canada’s vast forests have acted as a significant carbon sink with the “power to sequester more than a hundred megatonnes of carbon dioxide equivalent each year”. Natural Resources Canada “tracks the estimations of carbon released and captured . . . And Canada’s forests have not captured more carbon than they’ve emitted since 2001”.

Unseasonable or extreme drought, fire or pests are the most significant contributors to this shift. Our forests now contribute to our overall emission levels, which reached 716 megatonnes of carbon in 2017.

A healthy tree has a long lifespan. In fact, some live for centuries. Trees are resilient and can survive, thrive and regenerate in the presence of natural disturbances like drought, fire and insect infestation, and yet climate change has increased the severity and the frequency of these disturbances to the point where the forest cannot adapt quickly enough. 

 

So how can we create forests that are resilient to these changing conditions?