Mad About Science: The value of mature trees

By Brenden Bobby
Reader Columnist

This topic was suggested by community member, Julie Perchynski. Thanks, Julie!

It’s hard to throw a stone in Bonner County without hitting a tree. Though they seem overabundant, they provide benefits to human beings at all stages of life. We often discount mature trees as a source of firewood or lumber, but did you know that trees actually alter the environment in which they inhabit? This environmental alteration pays off in unexpected ways for humans.

The first and most obvious value of a large mature deciduous tree is its shade. In 2016, it was projected that a tree planted on a house’s western side would reduce energy consumption of the home by as much as 12% over 15 years. As temperatures and fuel prices have increased globally in the past seven years, this figure has likely grown. Shade provided by the tree lowers the heat within the home transferred by energy from the sun.

The average power bill for a residential home swings between $95 and $150 a month. Splitting the difference at $125 a month, this would create $2,700 in savings over a 15-year period — not to mention, this would reduce the amount of fuel consumed during the same time, which helps us all in the long run.

This is the measurable value of a single mature tree. Adding additional trees, while producing diminishing returns when directly impacting your house, can reduce the average ground-level temperature and provide refuge for birds, insects, squirrels, chipmunks and other wild critters in our area — all of which help with species propagation for beneficial flora that include native berries such as thimbleberry, which feeds and houses creatures as small as bumble bees and as large as grizzly bears.

A mature oak tree. Courtesy photo.

The true magic of trees is in their ability to pull carbon from the atmosphere and transform it into building blocks. Using photosynthesis, plants are able to literally pull matter from the air by using photons from the sun to split carbon dioxide into carbon and two oxygen atoms. The tree will absorb the carbon and spit the oxygen out as waste, which is great for animals that need oxygen to survive. 

A single acre of forest can absorb up to six tons of carbon dioxide per year and spit out four tons of oxygen in the process. Young trees simply cannot compare here, as they take years of photosynthesizing carbon dioxide to reach a meaningful size for carbon storage.

Several years ago, I was exposed to an interesting perspective on carbon dioxide in our atmosphere that completely changed how I viewed energy, matter and the environment. Due to the law of conservation of matter, matter cannot be created or destroyed, but it can change shape during chemical reactions. In the case of gasoline, multiple changes occur here. Petroleum was algae a very long time ago, now fossilized into the oily black sludge we pump from the ground. In order for that algae to grow, it utilized photosynthesis to split carbon dioxide into carbon and oxygen, just like a tree, and in doing so retained a portion of the energy from that reaction. That energy was trapped for hundreds of millions of years, until we introduce a spark to it to create a controlled explosion — a spontaneous release of ancient sunlight that fuses carbon and oxygen back together to create CO2, much like what happens when we breathe, and the inverse of the process of photosynthesis in plants.

At this point, the effects of vehicle emissions on climate change simply becomes math. We’re not creating or destroying anything per se, we’re just undoing the action of billion-year-old plants in a brand new environment. Mathematically, as more vehicles hit the roadway and more adult trees are felled, an imbalance occurs and nature cannot keep up its cyclical processes.

Some species of trees have an incredible hidden talent that’s only present and noticeable once they’ve spent decades maturing. Sugar maples change their environment in a way that is unlike virtually any other tree on the planet — in fact, only six species of trees are known to utilize this special evolutionary trait. Hydraulic lift is a function of just a few trees in the world that pull water up from a deep taproot and then store it in the shallow lateral roots for later. Oftentimes, these trees will pull up more water than they actually need, which spreads to the nearby soil. 

This might seem wasteful, but it helps other plants and animals flourish around the base of the tree, which helps not only the local environment, but the tree itself in the long run. 

As the symbiotic and parasitic plants at the maple’s roots grow and die, they process chemicals the maple might not be able to use until after the plant’s death or consumption by local fauna. Trees love four things: sunlight, water, death and poop. This symbiotic sharing technique is virtually nonexistent in younger trees, and it’s not until much later in life that they are able to alter their environment in this way.

Care to test this idea? Examine the soil around a mature maple and the soil around a mature white pine tree. Rummage around in the soil and see if the consistency of the soil is different between them. It will be most noticeable between 6 a.m. and 10 a.m., once the tree has slowed down the hydraulic lift process.

One more hidden benefit of large mature trees is their ability to transpire water. Water evaporates from tree leaves throughout the day, adding to the water cycle. This water cannot be destroyed, so it instead becomes smaller, lighter and floats away. As temperatures fall at higher elevations in the atmosphere, the water begins to coalesce and form back into clouds or rain. Entire forest systems are able to create rain through transpiration. It’s likely that this is another hidden bonus to having a fully grown tree in your yard, as evaporative cooling will come into play in the surrounding air.

Stay curious, 7B.