Different Kinds of Air

A man, like  mouse, should have more than one avenue of escapeA man, like a mouse, should have more than one avenue of escape
Joris Hoefnagel (1542 – 1604)

                    Observations on Different Kinds of Air
. . . . I flatter myself that I have accidentally hit upon a method of restoring air which has been injured by the burning of candles, and that I have discovered at least one of the restoratives which nature employs for this purpose. It is vegetation. In what manner this process in nature operates, to produce so remarkable an effect, I do not pretend to have discovered; but a number of facts declare in favour of this hypothesis…
One might have imagined that, since common air is necessary to vegetable, as well as to animal life, both plants and animal had affected it in the same manner, and I own that I had that expectation, when I first put a sprig of mint into a glass-jar, standing inverted in a vessel of water; but when it had continued growing there for some months, I found that the air would neither extinguish a candle, nor was it at all inconvenient to a mouse, which I put into it.
…Accordingly, on the 17th of August 1771, I put a sprig of mint into a quantity of air, in which a wax candle had burned out, and found that, on the 27th of the same month, another candle burned perfectly well in it. This experiment I repeated, without least variation in the event, not less than eight or ten times in the remainder of the summer.
Joseph Priestley (24 March 1733 – 6 February 1804)

In 1771, about the time of the first stirrings of the industrial revolution and its appetite for fossil fuel, an English minister grasped key processes of the natural carbon cycle. In a series of ingenious experiments, Joseph Priestley found that flames and animals’ breath “injure” the air in a sealed jar, making it unwholesome to breathe. But a green sprig of mint, he found, could restore its goodness. Priestley could not name the gases responsible, but we know now that the fire and respiration used up oxygen and gave off carbon dioxide. The mint reversed both processes. Photosynthesis took up the carbon dioxide, converted it into plant tissue, and gave off oxygen as a by-product.

The world is just a bigger jar. Tens of billions of tons of carbon a year pass between land and the atmosphere: given off by living things as they breathe and decay and taken up by green plants, which produce oxygen. A similar traffic in carbon, between marine plants and animals, takes place within the waters of the ocean. And nearly a hundred billion tons of carbon diffuse back and forth between ocean and atmosphere.

In other words:
Alone in a sealed jar, a mouse would die from exhaled CO2. But as Priestley observed in 1771, adding a plant allows the mouse to thrive. In this proof of photosynthesis, the mint absorbed CO2, retained carbon for growth, and released oxygen


Du Bon Usage Des Arbres

lindenLinden Tree On A Bastion
Albrecht Dürer (1471 – 1528)



Frédéric Joignot, The Guardian

“Man is senescent, that is to say is programmed to die, but a plane tree is not,” says French botanist Francis Hallé. After its leaves have fallen, life begins again in the spring and the tree recovers its youthful genomes. If it is not subjected to accidents, diseases or humans, the plane tree could live for centuries.
The botanist knows of a 2,000-year-old olive tree in Roquebrune-Cap-Martin on the Côte d’Azur

Humans, with a mere 2 square metres of skin, underestimate the surface area of a tree. To calculate that you need to measure both sides of each leaf, add the surface of the trunk, the branches and boughs, the perennial and feeder roots and the absorbent root hairs, not forgetting the bark pockets. A 15-metre tree in leaf would cover a total area of 200 hectares, which is the size of Monaco. A tree doubles its weight when wet, and its entire surface breathes and allows us to breathe.

Hallé believes that arboreal photosynthesis is our best ally in the fight against global warming. Buffon’s plane tree, like all trees, absorbs quantities of carbon dioxide, responsible for greenhouse gases, and between 20% and 50% of matter produced by the tree, including wood, roots, leaves and fruit, is composed of CO2. When trees breathe they clean the atmosphere and retain CO2 and urban pollutants such as heavy metals, lead, manganese, industrial soot and nitrous oxide. These are stored in the wood. That is why we should refrain as much as possible from cutting down old trees. The older they are, the better they control pollutants.

At the same time, trees release oxygen that allows us to live. An adult human consumes about 700g of O2 per day, or 255kg per year. In that time, an average tree produces 15kg to 30kg, so about 10 trees are required to provide oxygen for one person. Trees also humidify and cool the atmosphere by evaporation and transpiration. A wooded area of 50 square metres brings the temperature down by 3.5C and increases the humidity by 50%. Leaf movement, especially in conifers, releases negative ions that are supposed to have beneficial effects on health and mood.


Trees Heal

Eugenio Gignous (1850-1906)

Here are some of the best reasons to plant and care for trees or defend a tree’s standing:

Trees combat the greenhouse effect

Global warming is the result of excess greenhouse gases, created by burning fossil fuels and destroying tropical rainforests. Heat from the sun, reflected back from the earth, is trapped in this thickening layer of gases, causing global temperatures to rise. Carbon dioxide (CO2) is a major greenhouse gas. Trees absorb CO2, removing and storing the carbon while releasing the oxygen back into the air. In one year, an acre of mature trees absorbs the amount of CO2 produced when you drive your car 26,000 miles.

Trees clean the air

Trees absorb odors and pollutant gases (nitrogen oxides, ammonia, sulfur dioxide and ozone) and filter particulates out of the air by trapping them on their leaves and bark.

Trees provide oxygen

In one year an acre of mature trees can provide enough oxygen for 18 people.

Trees cool the streets and the city

Average temperatures in Los Angeles have risen 6°F in the last 50 years as tree coverage has declined and the number of heat-absorbing roads and buildings has increased.

Trees cool the city by up to 10°F, by shading our homes and streets, breaking up urban “heat islands” and releasing water vapor into the air through their leaves.

Trees conserve energy

Three trees placed strategically around a single-family home can cut summer air conditioning needs by up to 50 percent. By reducing the energy demand for cooling our houses, we reduce carbon dioxide and other pollution emissions from power plants.

Trees save water

Shade from trees slows water evaporation from thirsty lawns. Most newly planted trees need only fifteen gallons of water a week, the equivalent of two toilet flushes. As trees transpire, they increase atmospheric moisture.

Trees help prevent water pollution

Trees reduce runoff by breaking rainfall thus allowing the water to flow down the trunk and into the earth below the tree. This prevents stormwater from carrying pollutants to the ocean. When mulched, trees act like a sponge that filters this water naturally and uses it to recharge groundwater supplies.

Trees help prevent soil erosion

On hillsides or stream slopes, trees slow runoff and hold soil in place.

Trees shield children from ultra-violet rays

Skin cancer is the most common form of cancer in the United States. Trees reduce UV-B exposure by about 50 percent, thus providing protection to children on school campuses and playgrounds – where children spend hours outdoors.

Trees provide food

An apple tree can yield up to 15-20 bushels of fruit per year and can be planted on the tiniest urban lot. Aside from fruit for humans, trees provide food for birds and wildlife.

Trees heal

Studies have shown that patients with views of trees out their windows heal faster and with less complications. Children with ADHD show fewer symptoms when they have access to nature. Exposure to trees and nature aids concentration by reducing mental fatigue.

Trees reduce violence

Neighborhoods and homes that are barren have shown to have a greater incidence of violence in and out of the home than their greener counterparts. Trees and landscaping help to reduce the level of fear.

Trees mark the seasons

Is it winter, spring, summer or fall? Look at the trees.

Trees create economic opportunities

Fruit harvested from community orchards can be sold, thus providing income. Small business opportunities in green waste management and landscaping arise when cities value mulching and its water-saving qualities. Vocational training for youth interested in green jobs is also a great way to develop economic opportunities from trees.

Trees are teachers and playmates

Whether as houses for children or creative and spiritual inspiration for adults, trees have provided the space for human retreat throughout the ages. 

Trees bring diverse groups of people together

Tree plantings provide an opportunity for community involvement and empowerment that improves the quality of life in our neighborhoods. All cultures, ages, and genders have an important role to play at a tree planting or tree care event.

Trees add unity

Trees as landmarks can give a neighborhood a new identity and encourage civic pride.

Trees provide a canopy and habitat for wildlife

Sycamore and oak are among the many urban species that provide excellent urban homes for birds, bees, possums and squirrels.

Trees block things

Trees can mask concrete walls or parking lots, and unsightly views. They muffle sound from nearby streets and freeways, and create an eye-soothing canopy of green. Trees absorb dust and wind and reduce glare.

Trees increase property values

The beauty of a well-planted property and its surrounding street and neighborhood can raise property values by as much as 15 percent.

Trees increase business traffic

Studies show that the more trees and landscaping a business district has, the more business will flow in. A tree-lined street will also slow traffic – enough to allow the drivers to look at the store fronts instead of whizzing by.
To learn about different types of trees and view photographs, visit the
SelecTree website.

To receive up to seven free trees, please contact Trees For a Green LA (City of Los Angeles residents only).

To learn about protecting trees in your community please see