Forests and Climate Change


Forests cover around 31% of the world's total land area and provide livelihood and subsistence for about 1.6 billion people around the world. Humans and most life on land owe our existence to trees and forests which generate about half of all oxygen on the planet, oceans providing the remaining 50%.

To avoid the worst of the climate crisis, the absolute priority today is that all sectors of the economy radically and rapidly reduce their greenhouse gas emissions to zero. However, there is scientific consensus that limiting global warming to 1.5 degrees, a globally agreed target, will also require removing carbon dioxide from the atmosphere, by creating negative emissions. The only effective tool we currently have available to us, that we can actively apply and plant, are trees. The larger the tree, the bigger its surface and mass, the more CO2 the tree can draw down and sink into its mass and into the soils. Therefore, the most valuable trees for draw down are the biggest and oldest ones and we must protect existing mature and old growth forests. Planting trees now will be very important to help future generations manage the climate, but our imperative for the next decades, is to preserve existing forests. 

Not all forests are equal. I.e. a Tree farm is a plantation of trees for timber harvest - it is a monocrop culture with little value for wildlife, soils, and water - however it is counted by our governments as a forest. A working forest is one that periodically and systematically gets upended for logging and other forest management practices - this harms wildlife, prevents natural succession and permeates an edge effect across all forests not allowing them to become old growth. Forests "in conservation" are also widely managed, thinned, logged, replanted, etc. A forest in conservation only means that the land will not be paved over. What we need, and what the IPCC is calling for is forest preservation or proforestation, forest restoration, and rewilding. We must allow forests to grow old and become self-balancing ecosystems again.

To help clean the air we need to let trees and forests create negative emissions or 'draw down.'  This removes carbon from the air and is followed by carbon storage into what is known as a 'carbon sink.' The two largest carbon sinks are the ocean and mature and old growth forests. Forests clean our air and our water; they generate fertile soils which ensures food security in the long run; and,  they provide habitat and nutrients to over 80% of life on land.  So how do forests draw down greenhouse gases  ("GHG") from the atmosphere?

As trees grow, they absorb carbon dioxide from the air, converting the CO2 into plant matter by way of photosynthesis. A mature tree averages an uptake of 48 lbs. of carbon a year and can store at least half of this in their mass (also called 'woody biomass'.) Scientists call this process carbon sequestration. The plants keep the C, and respire the O2

In addition, trees sink carbon into the soils when the carbon dioxide (CO2) molecules in the air are captured and plant carbon is pushed below ground via the roots. As trees decompose, they also release carbon into the soils. We call this soil carbon. It is estimated that up to 50-70% of a forest's stored carbon is linked to mycorrhizal fungi that grow along tree-root systems and help keep them healthy. This is the key reason why we need to protect and preserve mature and old growth forests and not disturb these amazing carbon sinks through logging or fire which would release the stored carbon back into the air. 

We have often heard that forests are the lungs of the planet: they soak up carbon dioxide and breathe out oxygen. But scientists have also discovered that forests are biotic pumps - much like a heart- as forests have complex self-sustaining rainmaking systems - a major driver of atmospheric circulation on Earth.  

Forests are rainmakers as they attract and even create their own moisture-heavy clouds through evapotranspiration. A trees' roots capture water from the soil for photosynthesis, and microscopic pores in leaves release unused water as vapor into the air. The process is known as evapotranspiration. In this way, a single mature tree can release hundreds of liters of water a day. With its foliage offering abundant surface area for the exchange, a forest can often deliver more moisture to the air than evaporation from a water body of the same size. Thus, forests are key to maintaining moisture in the air and distributing it to all life.

As forests recycle vast amounts of moisture into the air they create "flying rivers" which also generate winds that pump that water around the world and distribute it.  When water vapor from forests condenses into clouds, a gas becomes a liquid that occupies less volume. That reduces air pressure, and draws in air horizontally from areas with less condensation which creates wind. This wind carries the moisture (flying river) inland which will eventually condensate and fall as rain. This happens across all forests but the larger the forested area, the more powerful the pump. According to researchers, the Amazon flying river for example transports as much moisture as the Amazon River itself.

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Due to the increasing temperatures caused by climate change, the growth window for trees is now longer (winters have become shorter), coupled with increased amounts of CO2 in the air, trees are growing up to 30% larger and faster than they did just several decades ago. Unfortunately, the wood is less dense for this same reason making trees weaker.

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Due to the very quickly warming temperatures and changes in precipitation, the vegetation and growth zones are in flux and nature cannot keep up with the changes. In order to try to help nature, conservationists have started 'assisted migration' whereby we plant trees that usually grow in warmer climates further north, or higher up, in the hopes that the species will survive.

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Storms and wildfires are natural and necessary occurrences where nature resets forest succession to an earlier stage. 

Fires reset ecosystems, restore heterogeneous patterns of plants, can reduce fuel loads, allow pyrophytic plants to germinate, and renew fire-dependent ecosystems. The increased heat, however, has made our forests drier and more susceptible to bigger and hotter wildfires. The Forest Service has thinned forests in order to try to reduce fuel loads, however, this appears to have accelerated wildfires and made them more intense.  

"Thinning" is a logging operation which, according to many wildfire experts, in itself upends any forest ecosystem; thinning opens the forest canopy allowing the forest floor to dry out faster; and, more air between the trees allows for fires to be accelerated by wind and grow exponentially hotter. 

The truth is that we are in unchartered territory and cannot predict how fires will evolve with climate change. However, forest management for fire should probably not include thinning and we must reduce active burning in anticipation of natural fires growing more common.  According to the experts, hardening the communities against forest fires, not building in forested areas, enlarging fire breaks, and preventing sparks from utilities, trains, and human activities is the key.

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In addition to the above climate change impacts to forests, same as humans who are now more exposed to new mutating pathogens and viruses, forests are exposed to new plant disease outbreaks, invasive plant life, and pests. These can pose significant risks to our forests - especially non-primary forests since these are more homogenous and disease can take over quickly. This is a big concern for global food security, and environmental sustainability worldwide. In addition, many pests are traveling farther and evolving faster, affecting previously not endangered forests. Pathogen ranges are also shifting, increasing the spread of plant diseases in new areas.  The best we can do to avoid accelerating the spread of disease is leaving forests intact, not logging, and not building roads and pathways through them.

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