Trees | Gentle Reading To Help You Sleep

Unwind with this calm bedtime reading on trees, designed to help you relax and drift into sleep while easing insomnia. Trees have shaped our world, and this gentle reading offers both learning and peace for restful nights. Discover their roles in nature, culture, and history, all delivered in Benjamin’s soothing cadence. There’s no whispering or hypnosis—just calm, fact-filled narration to ease stress, anxiety, and sleeplessness. Press play, settle in, and let your mind gently wander among the forests of knowledge.

Transcript

Welcome to the I Can't Sleep podcast,

Where I help you drift off one fact at a time.

I'm your host,

Benjamin Boster,

And today's episode is about trees.

In botany,

A tree is a perennial plant with an elongated stem or trunk,

Usually supporting branches and leaves.

In some usages,

The definition of a tree may be narrower,

E.

G.

,

Including only woody plants with secondary growth,

Only plants that are usable as lumber,

Or only plants above a specified height.

Trees are not a monophyletic taxonomic group,

But consist of a wide variety of plant species that have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight.

The majority of tree species are angiosperms or hardwoods.

Of the rest,

Many are gymnosperms or softwoods.

Trees tend to be long-lived,

Some trees reaching several thousand years old.

Trees evolved around 400 million years ago,

And it is estimated that there are around 3 trillion mature trees in the world currently.

A tree typically has many secondary branches supported clear of the ground by the trunk,

Which typically contains woody tissue for strength and vascular tissue to carry materials from one part of the tree to another.

For most trees,

The trunk is surrounded by a layer of bark,

Which serves as a protective barrier.

Below the ground,

The roots branch and spread out widely.

They serve to anchor the tree and extract moisture and nutrients from the soil.

Above ground,

The branches divide into smaller branches and shoots.

The shoots typically bear leaves,

Which capture light energy and convert it into sugars by photosynthesis,

Providing the food for the tree's growth and development.

Trees usually reproduce using seeds.

Flowering plants have their seeds inside fruits,

While conifers carry their seeds in cones,

And tree ferns produce spores instead.

Although tree is a common word,

There is no universally recognized precise definition of what a tree is,

Either botanically or in common language.

In its broadest sense,

A tree is any plant with the general form of an elongated stem or trunk,

Which supports the photosynthetic leaves or branches at some distance above the ground.

Trees are typically defined by height,

With smaller plants from 0.

5 to 10 meters being called shrubs,

So the minimum height of a tree is only loosely defined.

Large herbaceous plants,

Such as papaya and bananas,

Are trees in this broad sense.

A commonly applied narrower definition is that a tree has a woody trunk formed by secondary growth,

Meaning that the trunk thickens each year by growing outwards,

In addition to the primary upwards growth from the growing tip.

Under such a definition,

Herbaceous plants,

Such as palms,

Bananas,

And papayas,

Are not considered trees regardless of their height,

Growth form,

Or stem girth.

Certain monocots may be considered trees under a slightly looser definition.

While the Joshua tree,

Bamboos,

And palms do not have secondary growth,

And never produce true wood with growth rings,

They may produce pseudowood by lignifying cells formed by primary growth.

Tree species in the genus Dracaena,

Despite also being monocots,

Do have secondary growth caused by meristem in their trunk,

But it is different from the thickening meristem found in Dicotyledonus trees.

Aside from structural definitions,

Trees are commonly defined by use,

For instance,

As those plants which yield lumber.

The tree growth habitat is an evolutionary adaptation found in different groups of plants.

By growing taller,

Trees are able to compete better for sunlight.

Trees tend to be tall and long-lived,

Some reaching several thousand years old.

Several trees are among the oldest organisms now living.

Trees have modified structures,

Such as thicker stems composed of specialized cells,

That add structural strength and durability,

Allowing them to grow taller than many other plants and to spread out their foliage.

They differ from shrubs,

Which have a similar growth form,

By usually growing larger and having a single main stem.

But there is no consistent distinction between a tree and a shrub,

Made more confusing by the fact that trees may be reduced in size under harsher environmental conditions,

Such as on mountains and sub-Arctic areas.

The tree form has evolved separately in unrelated classes of plants,

In response to similar environmental challenges,

Making it a classic example of parallel evolution.

With an estimated 60,

000 to 100,

000 species,

The number of trees worldwide might total 25% of all living plant species.

The greatest number of these grow in tropical regions.

Many of these areas have not yet been fully surveyed by botanists,

Making tree diversity and ranges poorly known.

The majority of tree species are angiosperms or hardwoods.

Of the rest,

Many are gymnosperms or softwood trees.

These include conifers,

Cycads,

Gingivites,

And atollies,

Which produce seeds which are not enclosed in fruits,

But in open structures such as pine cones,

And many have tough,

Waxy leaves,

Such as pine needles.

Most angiosperm trees are eudicots,

The true dicotyledons,

So named because the seeds contain two cotyledons or seed leaves.

There are also some trees among the old lineages of flowering plants called basal angiosperms or paleodicots.

These include ambarella,

Magnolia,

Nutmeg,

And avocado,

While trees such as bamboo,

Palms,

And bananas are monocots.

Wood gives structural strength to the trunk of most types of tree.

This supports the plant as it grows larger.

The vascular system of trees allows water,

Nutrients,

And other chemicals to be distributed around the plant,

And without it,

Trees would not be able to grow as large as they do.

Trees need to draw water high up the stem through the xylem from the roots by capillary action,

As water continually evaporates from the leaves in the process of transpiration.

If insufficient water is available,

The leaves will die.

The three main parts of trees include the root,

Stem,

And leaves.

They are integral parts of the vascular system,

Which interconnects all the living cells.

In trees and other plants that develop wood,

The vascular cambium allows the expansion of vascular tissue that produces woody growth.

Because this growth ruptures the epidermis of the stem,

Woody plants also have a cork cambium that develops among the phloem.

The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss.

Both the production of wood and the production of cork are forms of secondary growth.

Trees are either evergreen,

Having foliage that persists and remains green throughout the year,

Or deciduous,

Shedding their leaves at the end of the growing season and then having a dormant period without foliage.

Most conifers are evergreens,

But larches are deciduous,

Dropping their needles each autumn.

And some species of cypress shed small leafy shoots annually in a process known as cladoptosis.

The crown is the spreading top of a tree,

Including the branches and leaves,

While the uppermost layer in a forest formed by the crowns of the trees is known as the canopy.

A sapling is a young tree.

Many tall palms are herbaceous monocots,

Which do not undergo secondary growth and never produce wood.

In many tall palms,

The terminal bud on the main stem is the only one to develop,

So they have unbranched trunks with large spirally arranged leaves.

Some of the tree ferns,

Order Scyatheales,

Have tall straight trunks growing up to 20 meters,

But these are composed not of wood but of rhizomes,

Which grow vertically and are covered by numerous adventitious roots.

The number of trees in the world,

According to a 2015 estimate,

Is 3.

04 trillion,

Of which 1.

39 trillion,

Around 46%,

Are in the tropics or subtropics,

0.

61 trillion,

Around 20%,

In the temperate zones,

And 0.

74 trillion,

Around 24%,

In the coniferous boreal forests.

The estimate is about 8 times higher than previous estimates and is based on tree densities measured on over 400,

000 plots.

It remains subject to a wide margin of error,

Not least because the samples are mainly from Europe and North America.

The estimate suggests that about 15 billion trees are cut down annually and about 5 billion are planted.

In the 12,

000 years since the start of human agriculture,

The number of trees worldwide has decreased by 46%.

There are approximately 64,

100 known tree species in the world.

With 43% of all tree species,

South America has the highest biodiversity,

Followed by Eurasia,

22%,

Africa,

16%,

North America,

15%,

And Oceania,

11%.

In suitable environments such as the Daintree Rainforest in Queensland or the mixed potocarp and broadleaf forests of Oliva Island,

New Zealand,

Forest is the more or less stable climatic climax community at the end of a plant succession,

Where open areas such as grassland are colonized by taller plants,

Which in turn give way to trees that eventually form a forest canopy.

In cool temperate regions,

Conifers often predominate.

A widely distributed climax community in the far north of the northern hemisphere is most taiga or northern coniferous forest,

Also called boreal forest.

Taiga is the world's largest land biome,

Forming 29% of the world's forest cover.

The long cold winter of the far north is unsuitable for plant growth,

And trees must grow rapidly in the short summer season when the temperature rises and the days are long.

Light is very limited under their dense cover,

And there may be little plant life on the forest floor,

Although fungi may abound.

Similar woodland is found on mountains,

Where the altitude causes the average temperature to be lower,

Thus reducing the length of the growing season.

Where rainfall is relatively evenly spread across the seasons in temperate regions,

Temperate broadleaf and mixed forest typified by species like oak,

Beech,

Birch,

And maple is found.

Temperate forest is also found in the southern hemisphere,

As for example in the eastern Australia temperate forest,

Characterized by eucalyptus forest and open acacia woodland.

In tropical regions with a monsoon or monsoon-like climate,

Where a drier part of the year alternates with a wet period,

As in the Amazon rainforest,

Different species of broadleaved trees dominate the forest,

Some of them being deciduous.

In tropical regions with a drier savanna climate and insufficient rainfall to support dense forests,

The canopy is not closed,

And plenty of sunshine reaches the ground,

Which is covered with grass and scrub.

Acacia and baobab are well adapted to living in such areas.

The roots of a tree serve to anchor it to the ground and gather water and nutrients to transfer to all parts of the tree.

They are also used by reproduction,

Defense,

Survival,

Energy storage,

And many other purposes.

The radical or embryonic root is the first part of a seedling to emerge from the seed during the process of germination.

This develops into a taproot,

Which goes straight downwards.

Within a few weeks,

Lateral roots branch out of the side of this and grow horizontally through the upper layers of the soil.

In most trees,

The taproot eventually withers away and the widespread laterals remain.

Near the tip of the finer roots are called cell root hairs.

These are in immediate contact with the soil particles and can absorb water and nutrients,

Such as potassium and solution.

The roots require oxygen to respire,

And only a few species,

Such as mangroves and the pond cypress,

Can live in permanently waterlogged soil.

In the soil,

The roots encounter the hyphae of fungi.

Many of these are known as mycorrhiza and form a mutualistic relationship with the tree roots.

Some are specific to a single tree species,

Which will not flourish in the absence of its mycorrhizal associate.

Others are generalists and associate with many species.

The tree acquires minerals,

Such as phosphorus,

From the fungus,

While the fungus obtains the carbohydrate products of photosynthesis from the tree.

The hyphae of the fungus can link different trees and a network is formed,

Transferring nutrients and signals from one place to another.

The fungus promotes growth of the roots and helps protect the trees against predators and pathogens.

It can also limit damage done to a tree by pollution,

As the fungus accumulates heavy metals within its tissues.

Fossil evidence shows that roots have been associated with mycorrhizal fungi since the early Paleozoic,

400 million years ago,

When the first vascular plants colonized dry land.

Some trees,

Such as alder,

Have a symbiotic relationship with Francia species,

A filamentous bacterium that can fix nitrogen from the air,

Converting it into ammonia.

They have actinorhizal root nodules on their roots,

In which the bacteria live.

This process enables the tree to live in low-nitrogen habitats,

Where they would otherwise be unable to thrive.

The plant hormones,

Called cytokinins,

Initiate root nodule formation in a process closely related to mycorrhizal association.

It has been demonstrated that some trees are interconnected through their root system,

Forming a colony.

The interconnections are made by the inosculation process,

A kind of natural grafting or welding of vegetal tissues.

The tests to demonstrate this networking are performed by injecting chemicals,

Sometimes radioactive,

Into a tree,

And then checking for its presence in neighboring trees.

The roots are generally an underground part of the tree,

But some tree species have evolved roots that are aerial.

The common purposes for aerial roots may be of two kinds,

To contribute to the mechanical stability of the tree and to obtain oxygen from air.

An instance of mechanical stability enhancement is the red mangrove that develops prop roots that loop out of the trunk and branches and descend vertically into the mud.

A similar structure is developed by the Indian banyan.

Many large trees have buttress roots,

Which flare out from the lower part of the trunk.

These brace the tree rather like angle brackets and provide stability,

Reducing sway in high winds.

They are particularly prevalent in tropical rainforests where the soil is poor and the roots are close to the surface.

Some tree species have developed root extensions that pop out of the soil in order to get oxygen when it is not available in the soil because of excess water.

These root extensions are called pneumatophores and are present,

Among others,

In black mangrove and pond cypress.

The main purpose of the trunk is to raise the leaves above the ground,

Enabling the tree to overtop other plants and outcompete them for light.

It also transports water and nutrients from the roots to the aerial parts of the tree and distributes the food produced by the leaves to all other parts,

Including the roots.

In the case of angiosperms and gymnosperms,

The outermost layer of the trunk is the bark,

Mostly composed of dead cells of phellum,

Cork.

It provides a thick,

Waterproof covering to the living inner tissue.

It protects the trunk against the elements,

Disease,

Animal attack and fire.

It is perforated by a large number of fine,

Breathing pores called lenticles,

Through which oxygen diffuses.

Bark is continually replaced by a living layer of cells called the cork cambium or phellagen.

The London Plain periodically sheds its bark in large flakes.

Similarly,

The bark of the silver birch peels off and strips.

As a tree's girth expands,

Newer layers of bark are larger in circumference,

And the older layers develop fissures in many species.

In some trees,

Such as the pine,

The bark exudes sticky resin,

Which deters attackers,

Whereas in rubber trees it is a milky latex that oozes out.

The quinine bark tree contains bitter substances to make the bark unpalatable.

Large tree-like plants with lignified trunks in the pteridophyta,

Auricules,

Cycadophyta and poales,

Such as tree ferns,

Palms,

Cycads and bamboos,

Have different structures and outer coverings.

Although the bark functions as a protective barrier,

It is itself attacked by boring insects,

Such as beetles.

These lay their eggs in crevices,

And the larvae choose their way through the cellulose tissues,

Leaving a gallery of tunnels.

This may allow fungal spores to gain admittance and attack the tree.

Dutch elm disease is caused by a fungus carried from one elm tree to another by various beetles.

The tree reacts to the growth of the fungus by blocking off the xylem tissue,

Carrying sap upwards and the branch above,

And eventually the whole tree is deprived of nourishment and dies.

In Britain in the 1990s,

25 million elm trees were killed by this disease.

The innermost layer of bark is known as the phloem,

And this is involved in the transport of the sap containing the sugars made by photosynthesis to other parts of the tree.

It is a soft,

Spongy layer of living cells,

Some of which are arranged end-to-end to form tubes.

These are supported by parenchyma cells,

Which provide padding and include fibers for strengthening the tissue.

Inside the phloem is a layer of undifferentiated cells one cell thick,

Called the vascular cambium layer.

The cells are continually dividing,

Creating phloem cells on the outside and wood cells known as xylem on the inside.

The newly created xylem is the sapwood.

It is composed of water-conducting cells and associated cells which are often living and is usually pale in color.

It transports water and minerals from the roots to the upper parts of the tree.

The oldest inner part of the sapwood is progressively converted into heartwood as new sapwood is formed at the cambium.

The conductive cells of the heartwood are blocked in some species.

Heartwood is usually darker in color than the sapwood.

It is the dense central core of the trunk,

Giving it rigidity.

Three quarters of the dry mass of the xylem is cellulose,

A polysaccharide,

And most of the remainder is lignin,

A complex polymer.

A transverse section through a tree trunk or a horizontal core will show concentric circles of lighter or darker wood,

Tree rings.

These rings are the annual growth rings.

There may also be rays running at right angles to growth rings.

These are vascular rays,

Which are thin sheets of living tissue permeating the wood.

Many older trees may become hollow but may still stand upright for many years.

Trees do not usually grow continuously throughout the year,

But mostly have spurts of active expansion followed by periods of rest.

This pattern of growth is related to climatic conditions.

Growth normally ceases when conditions are either too cold or too dry.

In readiness for the inactive period,

Trees form buds to protect the meristem,

The zone of active growth.

Before the period of dormancy,

The last few leaves produced at the tip of a twig form scales.

These are thick,

Small,

And closely wrapped and enclose the growing point in a waterproof sheath.

Inside this bud there is a rudimentary stalk and neatly folded miniature leaves,

Ready to expand when the next growing season arrives.

Buds also form in the axils of the leaves,

Ready to produce new side shoots.

A few trees,

Such as the eucalyptus,

Have naked buds with no protective scales,

And some conifers,

Such as the Lawson's cypress,

Have no buds but instead have little pockets of meristem concealed among the scale-like leaves.

When growing conditions improve,

Such as the arrival of warmer weather and the longer days associated with spring and temperate regions,

Growth starts again.

The expanding shoot pushes its way out,

Shedding the scales in the process.

These leave behind scars on the surface of the twig.

The whole year's growth may take place in just a few weeks.

The new stem is un-lignified at first and may be green and downy.

The palms have their leaves spirally arranged on an unbranched trunk.

In some tree species in temperate climates,

A second spurt of growth,

A lamus growth,

May occur,

Which is believed to be a strategy to compensate for loss of early foliage to insect predators.

Primary growth is the elongation of the stems and roots.

Secondary growth consists of a progressive thickening and strengthening of the tissues as the outer layer of the epidermis is converted into bark and the cambium layer creates new phloem and xylem cells.

The bark is inelastic.

Eventually the growth of a tree slows down and stops and it gets no taller.

If damage occurs,

The tree may in time become hollow.

Leaves are structures specialized for photosynthesis and are arranged on the tree in such a way as to maximize their exposure to light without shading each other.

They are an important investment by the tree and may be thorny or contain phytoliths,

Lignans,

Tannins,

Or poisons to discourage herbivory.

Trees have evolved leaves in a wide range of shapes and sizes in response to environmental pressures including climate and predation.

They can be broad or needle-like,

Simple or compound,

Lobed or entire,

Smooth or hairy,

Delicate or tough,

Deciduous or evergreen.

The needles of coniferous trees are compact but are structurally similar to those of broad-leaved trees.

They are adapted for life in environments where resources are low or water is scarce.

Frozen ground may limit water availability and conifers are often found in colder places at higher altitudes and higher latitudes than broad-leaved trees.

In conifers such as fir trees,

The branches hang down at an angle to the trunk enabling them to shed snow.

In contrast,

Broad-leaved trees in temperate regions deal with winter weather by shedding their leaves.

When the days get shorter and the temperature begins to decrease the leaves no longer make new chlorophyll and the red and yellow pigments already present in the blades become apparent.

Synthesis in the leaf of a plant hormone called auxin also ceases.

This causes the cells at the junction of the petiole and the twig to weaken until the joint breaks and the leaf floats to the ground.

In tropical and subtropical regions,

Many trees keep their leaves all year round.

Individual leaves may fall intermittently and be replaced by new growth but most leaves remain intact for some time.

Other tropical species and those in arid regions may shed all their leaves annually such as at the start of the dry season.

Many deciduous trees flower before the new leaves emerge.

A few trees do not have true leaves but instead have structures with similar external appearances such as phyloclades,

Modified stem structures,

As seen in the genus Phytoclatus.

Reviews

I do not, for the life of me, remember any of this, thank you so much!

Thank you for another “riveting” subject. 😂😂
Although I am a tree hugger so…..💜💜
Thank you, Benjamin!! 😻😻

Nice one

Can you please make a med about the rubiks cube

I listen to these because I love the subjects and this is one of my favorites! I did also fall asleep despite trying not to :)

Your talks soothe my heart, especially in these times. I add your podcasts to my playlists automatically now.
I connect to trees every day, as well as this wonderful podcast. Thank you! 🙏