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When it Comes to the Climate, Look Up At the Mature Trees

Each year, humanity releases massive amounts of climate polluting, greenhouse gases to the atmosphere and destroys natural ecosystems triggering a planetary species extinction and climate crisis. The solution is simple – keep fossil fuels in the ground, transition to clean, renewable energy, and protect the wellsprings of life on Earth. Naturally, protecting mature forests from logging on federal lands can buy us time to reach a zero-carbon economy by drawing down atmospheric CO2, if we simply let them grow.

As trees age, grow taller and bigger, and the forest itself matures, they support more wildlife, develop richer soils, purify and slowly release water during dry summer months, and cleanse the air we breathe far better than logged forests.

A hike through a mature forest whether in Appalachia or Alaska reveals many of nature’s best kept secrets when viewed from the forest canopy (penthouse) to the forest soils (basement). In the forest penthouse, epiphytes – ferns, air plants, lichens and mosses – provide nesting platforms for hawks and owls. Many salamanders and tree voles live out their existence in small clumps of vegetation clinging to branches at the top of the tallest trees. On the forest floor, a bounty of wildflowers is manufacturing nectar and producing seeds for pollinating insects and small mammals. A yard of soil can harbor many more invertebrates and microbes, busy returning nutrients to plants, then those in the richest tropical rainforests. In the basement, an Avatar-like mycorrhizal fungal network connects plants chemically to each other, allowing them to exchange vital nutrients and “communicate” through the release of stress hormones that signal forest disease.

And when a tree falls in the forest, nature indeed does hear!

Tree death restarts the process of renewal by creating a gap in the dominant forest overstory, allowing sunlight to penetrate in support of seedlings and plants that gradually fill the gap. The most valuable ecosystem elements are the large, dead trees as they are homes for scores of wildlife. When dead trees eventually fall, their rotting trunks are transformed as “nursery logs” for seedlings, some of which might be the progeny of the dead parent tree. If the dead tree happens to fall into a stream, aquatic life will use it for hiding and resting cover. Death in the forest is not the end, but the beginning of a tightly knit ecosystem renewal process.

Mature forests are the planet’s lungs and cooling towers. In fact, trees are roughly a half- and-half mixture of water and carbon. Through the miracle of photosynthesis, plants absorb CO2 via tiny openings in their leaves (stomata), gather up water through leaves and roots, and use sunlight to catalyze the conversion of CO2 to glucose, a carbon-chain molecule that is food for plants. Oxygen is a byproduct of this essential process. At night, trees respire, and when they die, slowly return carbon to the atmosphere. Trees also release water via evapotranspiration that helps to make rain and keeps the mature forest cool in the summer. Contrast this with hotter, drier clearcuts.

While the rate of carbon accumulation in a single tree increases continuously for centuries, mature forests as a whole reach a dynamic equilibrium between uptake of carbon, respiration and mortality (homeostasis), acting both as a net carbon sink and carbon storage warehouse overtime.

Notably, mature forests have played an integral role in creating the climate “sweet-spot” during which humanity has prospered because temperatures were suitable for agriculture thousands of years ago. But, we now face two imminent choices – keep the carbon in mature forests, or send it back to the atmosphere at unprecedented rates and temperature increases.

If you think of the forest as a leaky bucket that reaches a dynamic equilibrium between intake and outtake of carbon over time in a natural state, logging punches much bigger holes in that bucket, quickly returning carbon to the atmosphere. Only a small amount of the forests’ carbon is stored temporarily in wood products or recovered from newly established trees. This is known as the carbon debt (or dead zone) because the young trees take years to ramp up photosynthesis and decades-centuries to catch up to the carbon stored in the mature forest. With the most recent climate projections of the Intergovernmental Panel on Climate Change warning of imminent climate calamities, UN Secretary General António Guterres issued a “code red emergency” to change course while there is precious little time. Logging mature forest just ups the ante on catastrophic outcomes.

In sum, mature forests store more carbon than any terrestrial ecosystem on the planet, purify our drinking water, cleanse the air we breathe, and are nature’s climate solutions. Protecting mature forests comes with a basket of ecosystem benefits, increasingly important in a climate and biodiversity emergency. So, the next time you are in mature forests, look up and pay attention to what they are giving you for free.

Dominick A. DellaSala, Chief Scientist, Wild Heritage, is an award-winning conservation scientist with over 250 peer-reviewed publications and books, including Conservation Science and Advocacy for a Planet in Peril: Speaking Truth to Power.


The Worth More Standing report spotlights federal forest-management practices that are liquidating mature and old-growth forests and trees every day. It includes 10 examples that are part of a pervasive pattern of federal forest mismanagement that routinely sidesteps science to turn carbon-storing giants into lumber. Learn what actions you can take to protect Climate Forests across the country.

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