The climate and ecosystems are moving polewards. Will trees be able to keep pace?
There is a bleak future outlined for our planet. Climate change and the dilemma it brings. We’ve all heard of it.
Global warming — rising global temperatures — is one of the biggest problems we face currently, and it’s setting off a chain of more events, like melting glaciers and rising sea levels, which mean that a lot of lands will eventually get submerged underwater.
It is mainly caused by a concentration of carbon dioxide in the atmosphere. So an effective way to slow it down is to get rid of all that carbon. But how?
Well, imagine a machine that could suck out all the carbon from the air, and convert it into something beneficial, like, say, oxygen. Luckily for us, these machines do exist.
I’m talking about trees of course!
Trees are often mentioned as a solution to counter climate change because they naturally capture carbon in a process called photosynthesis.
They use water, light, and carbon dioxide to build chains of carbon. These chains can be short and sweet like fructose and saccharose; or they can be long and create reserves of energy for the plant, for example, the starch in grains and potatoes. The plant reserves usually make for a delicious meal!
Other chains can be very long and are the backbone of the plant, for example, cellulose and lignin. Wood is made of cellulose and lignin which is basically a standing pole of chains of carbon. Even after the death of the tree, the wood can be preserved for a thousand years and prevent carbon from being released into the atmosphere.
But here is the twist. Carbon can be stored in a tree only if the tree can grow.
Climate change is changing the environmental conditions around the world.
Tree species that thrived for centuries are seeing their birthplace change. Cold places are becoming warmer, rain is falling at different times and hot places are becoming dryer. Trees can either migrate to greener pastures, disappear forever, or adapt to the change.
Trees have a plethora of coping mechanisms. For one, they could adapt to a warmer climate by changing their flowering time. In Japan, cherry blossoming has moved a week earlier compared to fifty years ago! Cherry trees used to blossom late to avoid frost; now that the risk of frost is gone, they don’t wait that long.
Trees can also put out smaller leaves, reducing their width and area to minimise transpiration and save water. Herbarium records have observed an Australian shrub, Dodonaea viscosa, using this very strategy. They grow in a wide range of places, but the higher you go, the smaller their leaves are.
Researchers concluded that temperatures cause these changes, with the plant reducing its leaf area at cold and high altitudes as well as near the warm and tropical climates.
A tree facing a drought can lose leaves and close its stomata to avoid losing water. Closing stomata at hot times stops photosynthesis. The tree needs to photosynthesise — literally, eat — at the right time of the day. Trees that don’t find ways to save water may die or have fewer seedlings.
A tree species can adapt to environmental change through generations; new seedlings being adapted to new conditions. In this case, tree species with a high number of seedlings, seeds able to travel long distances and short generation length will adapt more easily.
Less than one percent of tree species have become extinct; however, nearly a third are threatened.
Even though climate change comes last on the list of threats to trees — far behind many human activities like agriculture and mining — it’s still important to plan for it, especially for species we use every day like timber trees and orchards. In non-optimal conditions, trees reduce their number of fruits and experience slow growth.
Pests, diseases, and pollinators also adapt to climate change. Just like trees, they can change their life cycle, reproduce earlier, or move to other places.
Temperatures and rainfall are the biggest factors that influence the movement of pests and diseases. Generally, increasing rainfall and temperatures help pests thrive because the humid climate is great for breeding. Extremely high temperatures, however, tend to slow pest reproduction, and heavy rains wash off larvae from leaves. That’s why most pests favour temperate areas, with their average non-extreme temperatures. Rising levels of carbon dioxide create a friendly environment for fungi and other similar pathogens.
In fact, research has shown pest populations moving towards the poles, at an average of three kilometres a year. Even pests like the southern pine beetle have been following similar patterns, confirming their need for temperate regions, as well as the fact that the area falling under ‘temperate’ has been steadily increasing.
Such changes in insects’ lives affect trees, and should also be considered when planting trees in different locations. Trees with high production somewhere might lose this advantage due to pests, disease, or missing pollinators.
Breeding tree species resistant to dryer and warmer climates with commercial trees is another solution. All the trees and crops we use every day have a cousin and relative in the wild which can be used for breeding and plant improvement.
For example, we drink coffee from two species, Arabica and Robusta, but there are nearly 200 coffee species in the wild. Even within the Arabica species, there are wild populations with genetic diversity which may be able to better resist climate change.
Researchers in the 1950’s explored the highlands of Ethiopia to document the diversity of Coffea arabica. Germplasm or exemplars of different coffee populations were collected and studied in research centres across coffee countries. Commercial varieties of coffee were crossed with wild individuals showing resistance to certain pests to obtain high producing and pest-resistant trees.
Similarly, wild coffee trees losing fewer leaves during drought and from warmer areas can also be used to create hybrids resistant to climate change. Selected hybrids are often very vigorous and produce more than pure varieties.
When helping tree populations to move, new hybrids should be tested on the field in several locations to be sure it is adapted to a warmer and drier climate. The trees of the future should be able to keep a high growth and production even in dryer climates.
Because of climate change, timber trees will need more and more time to grow large and widen their trunks. A reduction in timber volume means less timber to build houses and furniture, as well as less money to the forester.
To avoid this problem, foresters help trees to migrate. For example, in Alberta, a region in the West of Canada, researchers took seeds of White Spruce in defined ecological zones to plant them in different areas. They are helping this species of tree crucial for the timber industry to migrate up north.
However, trees are very slow to grow. The results of such experiments can be observed years or even decades later. Only then, it is possible to understand which tree population fits the best in which area. Alberta has already warmed up by 0.8 °C in the last 25 years, and like the world, it is expected to warm even more. Moving tree seedlings to areas that are expected to warm up might not be quick enough.
Trees might be at the right place for the climate of tomorrow, but not for the climate of the day after tomorrow. We need to be two or three steps ahead, not just one.