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 a number of 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

that 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."

Heat islands

Durable dynamic systems have elements, or layers, that change at different rates. The fast layers that change quickly provide the 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 as the working structure of a robust and adaptable civilisation.

Time hierarchy

In some forests where the trees grow tall such as in the US Pacific Northwest when a giant tree falls, it can clear a patch of forest letting in light and providing a new surface for seedlings to take root, away from the competition of the forest floor.

Sometimes the nurse log is so successful as a sort of creche for the young trees that they will grow along the full length of the fallen trunk. And when the original log decays away it leaves a remarkable, straight line of trees.

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 fall. But what makes the leaves change colour and what compounds are responsible for Nature's spectacular display?

We all know the magical green chlorophyll, but leaves also contain carotenoids. As the chlorophyll fades, the golden oranges of these carotenoids start to shine through. You may recognise 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 that gives beautiful deep reds.

Autumn leaves and the compounds that cause their colours

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.

Also see: how owls’ necks turn so far around, or why do birds migrate so far.

The classic twit-twoo is actually a duet

A distinctive line below which you don’t tend to see leaves or branches in places with animals that like eating leaves or branches. Basically, caused by animals eating as high as they can reach — except for where there are giraffes where trees don’t stand much of a chance, even spiky ones.

The browse line

Trees that live on after toppling and that can create new trees from branches of the original with their own roots and everything. 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. When the original finally decays you end up with a neat straight line of trees.

Sketchplanations tagged with trees