Many trees and forests were built to live with fire and in many cases, fire is essential for a healthy ecosystem. Giant sequoias, for example, have cones that dry out during surface fires releasing their seeds so they can germinate at the ideal time to grow with less competition.

Ponderosa pines have a number of ways they have evolved to live with fire.

They have bark that when heated can split off from the tree protecting the trunk and reducing the spread of fire. 

They often lose lower branches, sometimes from smaller fires, reducing the likelihood of ladder fires that climb towards the crown.

The shade they cast and the acidic soil they favour helps reduce understory plants that could catch fire beneath the tree and help a fire to latch onto the main trunk.

They have deep roots that can remain intact after a fire allowing the tree to still gather water and nutrients even when surface roots are damaged.

Some policies of suppressing natural fires have changed the balance of many forest systems and helped promote some of the recent mega-fires.

More about the Fire ecology of ponderosa pines (pdf).

Also see: identify a douglas fir, time hierarchy

Ponderosa pine fire protections

Heat islands are urban areas that can have higher temperatures than surrounding rural areas with more greenery.

Heat islands are caused by several factors, including:

the types of materials we use in cities for buildings, pavement, and roads that can absorb more heat than natural surfaces such as leaves or grass

human additions to the sun's heat, such as air conditioning, vehicles, cooking, or machinery

the shapes of our cities that may restrict airflow to carry heat away

the mass of our buildings that can absorb heat and release it gradually, even through the night

More natural, often rural areas with greenery may reflect more light, release moisture and provide shade.

There are ways to help reduce the effect of heat islands, such as planting more urban trees or using green roofs.

Deciduous trees have the handy feature of providing shade for a house in the summer while letting light through in the winter when the leaves fall.

A study using 2015 data found that "doubling tree cover in European cities could cut the number of heat-related deaths during summer months by nearly 40 per cent." In Columbia's Medellín, creating 30 Green Corridors helped to reduce temperatures by 2°C in the first three years of the program.

Learn more about the heat island effect on the EPA site.

Heat islands

A time hierarchy example is how durable dynamic systems have elements, or layers, that change at different rates.

Just like for pace layers, the fast layers that change quickly provide innovation, while the slower layers stabilise and remember.

In his short article Pace Layering: How Complex Systems Learn and Keep Learning, Stewart Brand gives this evocative example of the time hierarchy of a coniferous forest:

"Take a coniferous forest.  The hierarchy in scale of pine needle, tree crown, patch, stand, whole forest, and biome is also a time hierarchy.  The needle changes within a year, the crown over several years, the patch over many decades, the stand over a couple of centuries, the forest over a thousand years, and the biome over ten thousand years.  The range of what the needle may do is constrained by the crown, which is constrained by the patch and stand, which are controlled by the forest, which is controlled by the biome.  Nevertheless, innovation percolates throughout the system via evolutionary competition among lineages of individual trees dealing with the stresses of crowding, parasites, predation, and weather.  Occasionally, large shocks such as fire or disease or human predation can suddenly upset the whole system, sometimes all the way down to the biome level."

It's an example of his wonderful framework of pace layers, which he applies to the working structure of a robust and adaptable civilisation.

Time hierarchy

In some forests where the trees grow tall and straight, like those in the US Pacific Northwest, when a giant tree falls it creates an opening in the forest canopy that lets in light for new growth to take foot.

The mighty fallen tree trunks themselves provide a new surface for seedlings to take root, away from the competition of the forest floor. When this happens, the fallen tree becomes an integral part of a new ecosystem.

Such fallen trees are known as nurse logs. Sometimes, a nurse log is so successful as a nursery for the young trees that they will grow along the full length of the fallen trunk. When the nurse log finally decays, it leaves behind a remarkable straight line of trees.

This sketch appears in my book Big Ideas Little Pictures

The finger-dip test to not overwater houseplants

Nurse log

What a lovely time of year—when the leaves of deciduous trees in many forests change from the deep greens of summer to the yellows, oranges and reds of autumn. But what makes the leaves change colour, and what compounds are responsible for nature's spectacular display?

Many of us will know the green of chlorophyll, but leaves also contain carotenoids. As the chlorophyll fades, the golden oranges of these carotenoids start to shine through. You may recognize one carotenoid, beta-carotene, from carrots.

Another carotenoid, xanthophyll, is responsible for the beautiful bright yellows.

The leaves of some trees also produce anthocyanin as autumn begins, which produces those beautiful deep reds.

This sketch features in my book Big Ideas Little Pictures

Autumn leaves and the compounds that cause their colours

If you lived on Easter Island, would you really cut down the last mighty tree knowing that would be it? It seems either foolhardy or desperate to knowingly cut down the last of a kind and your last source of timber. So how could it happen?

Jared Diamond, in his book Collapse and article Easter’s End, explains how this situation could happen through a gradual, hardly noticeable decline over many years. Those who remembered the great trees that they used to make rafts, canoes, and ships were old or had long since died. Today's trees may be nothing like the forests and towering trunks of tens or hundreds of years ago.

"Gradually trees became fewer, smaller, and less important. By the time the last fruit-bearing adult palm tree was cut, palms had long since ceased to be of economic significance. That left only smaller and smaller palm saplings to clear each year, along with other bushes and treelets. No one would have noticed the felling of the last small palm."

More recently, I read Rutger Bregman's story of Easter Island in his book Human Kind: A Hopeful History. In the chapter "The Mystery of Easter Island," he digs into the reconstruction provided by Diamond and others and questions whether the Easter Islanders really were reduced, after losing their trees, to infighting and destitution.

Bregman found evidence to suggest that rather than driving themselves to the brink of extinction, the Easter Islanders were likely still thriving when Peruvian slave traders arrived in 1862, and sixteen slave ships carried off a third of the island's population, 1,407 people.

Yet the worst for them was still to come a year later when the government was pressured to return the islanders home. A smallpox outbreak carried by the returning islanders wreaked devastation during the voyage, with hundreds dying at sea. The 15 islanders who made it home carried the virus with them, and it spread to the inhabitants who remained. He cites that the population was reduced to just 110 inhabitants in 1877 when the epidemic finally subsided.

Until the arrival of the slave ships, the population, despite their trials, was still thriving. Bregman suggests that it was, in fact, contact with the rest of the world that destroyed Easter Island.

For another thought-provoking perspective, Seth Godin asks who cut down the second-to-last-tree?

Who cut down the last tree?

Funny how it can take nearly 40 years to learn that something as commonplace as the stereotypical owl sound is made, not by one owl, but as a duet between the male and female tawny owls.

The classic twit-twoo is actually a duet

I love this term. From the Japanese shinrin-yoku, it means to soak in the atmosphere of a forest. And I think it’s not too far of an overstatement to say that a walk in Nature is about the closest to a miracle cure we have. There appear to be myriad benefits from simply spending time in Nature. As my sister put it, if it was a drug we’d be prescribing it.

Though we didn’t call it forest bathing at the time it’s definitely some of my happiest memories, like here, here, here, here, and here.

Forest bathing

The browse line is a distinctive line below which you don’t tend to see leaves or branches in places with ground animals, like deer, that enjoy eating leaves or branches.

Browse lines are basically caused by animals eating as high as they can reach. When everything below has been eaten, what's left behind can be a strikingly flat line of leaves at the base of the foliage.

Except for where there are giraffes or elephants where trees don’t stand much of a chance, even spiky ones.

This drawing is based on the beautiful Richmond Park in South West London which has a large number of old oaks and large herds of deer that leave a uniform underline to the canopy across the park.

The browse line

Phoenix trees are trees that live on after toppling and that can create new trees from branches of the original with their own roots and everything. They are named after the mythical phoenix, a bird that rises from the ashes to regenerate after death, much like Fawkes from Harry Potter.

In phoenix trees I've seen, a large toppled tree hasn't completely separated from its roots—where some roots are broken as the tree fell,  one side of the roots has managed to remain connected. This provides a lifeline for the now horizontal tree.

Remarkably, those branches along the trunk that are now growing upwards can become like trees in their own right and, at times, even put down their own roots. These side trees remain supported by the original great, toppled tree. 

Phoenix trees are not to be confused with nurse logs which are dead fallen trees that provide a great environment for new trees and plants to grow in.

Phoenix trees

How to identify a douglas fir? I find identifying the sometimes subtle differences of tall evergreens rather difficult, but fortunately, that's not the case for the douglas fir.

Identifying a douglas fir, a tall, straight and very impressive evergreen conifer is easy with this simple reminder if you find any cones. Normally, the cones are easy to find around the base of a tree. For such a large tree, like the redwood or sequoia, the cones are quite small.

Douglas fir cones have many small 3-pointed tongues (or bracts) that emerge from the tight cones. Typically, they are of unequal lengths with the longest in the centre. After it came to mind to name each one Dougie, Douglas, and Doug, in turn, after the length of each point, I haven’t forgotten since and identifying a douglas fir is easy.

Mature douglas firs typically have grey, tough and deeply-fissured bark to go with it.

The douglas fir, one of my favourite trees, might even have grown above the tallest redwoods living today making the douglas fir one of the tallest known trees.

The Douglas fir is named after Scottish botanist David Douglas and is not a true fir tree and so it's sometimes written Douglas-fir.

Also see: Ponderosa pine fire protections, nurse log, phoenix trees

Trees sketches