What is a forest?

Straightforward question, yes?  Well, according to Wikipedia, there isn’t a universally accepted definition.

“The unconscious wood has a long moment of perfect clarity at dawn, and from being dark and confused, lit from the east it is all clarity, all distinct, seen to be a place of silence and peace with it’s own order in disorder – the fallen trees don’t matter, they are all part of it.”
– Thomas Merton

DSC_0357 levels shadows contrast

So, instinctively we think we know what a forest is, it’s just a group of trees right?  Well, it’s much more than that.  It’s a community of trees and other organisms which interact within a complex web of relationships as we’ve seen.  Forests cover about a third of the earth’s land and are home to many of the world’s organisms.  They are found in a myriad of climates, there are rainforests, arboreal forests and so on.

There are also different categories.  In the UK, there are considered to be three types of woodland:

  • Primary woodland – existed continuously since last age
  • Secondary woodland – was previously unwooded but reverted back
  • Plantations – deliberately planted

Ancient woodland, that is land which has been continuously wooded since 1600, now makes up just 2% of the UK.  And these ancient trees are home to many specialised species.  The trees tend to be hollowed out by fungi which creates a steady temperature and humidity level within the tree allowing rare species to live there.

Forests, like plants in general, are critical to human existence.  We came from trees and we rely on them.  They influence weather and climate, act as huge carbon sinks, produce 60% of the world’s oxygen and filter dust and harmful bacteria out of the air we breathe.  Forests lead to increased soil fertility, they hold the soil in place, they provide shade and moderate the wind.  They offer protection from avalanches, they reduce noise and they are home to many important species.

Inside a forest, temperatures are often a little cooler but they are always steadier, there is lower fluctuation within a forest.  But here I am talking about forests as if they were homogeneous estates.  All forests are different and within each forest are layers of specialised habitats.

Canopy – Here, the tallest trees eg oak, ash and beech reach up with long branches and leaves.  We know very little about life in the canopy as many of them remain unexplored.  However, we do know that the canopy layer plays and important role in forest life.  They affect the weather in the forests, they contribute to nutrient cycling and provide habitat for plants and animals including birds and insects and some mammals.

Sunlight and rain reach the canopy before any other part of the forest making it potential warmer and wetter than below, although the rain is not trapped in the canopy layer as it is further down so it’s less humid than the forest beneath.  The canopy, as well as increasing humidity, also blocks light and wind from reaching the forest floor affecting the microclimate of the entire forest and thus what can thrive there.

Understory – Just beneath the canopy are the tops of shorter trees and shrubs which can survive with less light eg hawthorn and hazel.  This layer of forest tends to be more humid than the rest and so it doesn’t dry out as easily.  These conditions are great for ferns, mosses and fungi which flourish here.  Again, in terms of animals, we’re looking at birds, insects and some mammals.

Herb/field layer – This is where we find the ferns, grasses and flowering plants which cover the forest floor.  These plants tend to bloom in early spring so that they can utilise the sunlight before the trees grow their leaves and the canopy makes the forest darker.  Here we also find herbivores which eat the plants, such as rabbits, and creatures which eat the herbivores, such as foxes.

Ground layer – This layer is full of dead matter such as rotting leaves and fallen branches.  It is also home to fungi and a variety of insects which help the decomposition process.  This releases nutrients into the soil which the trees and other plants take up.  It is where we find spiders and beetles and ants, hiding in the dark forest floor.

The forest floor acts as a bridge between the life above ground and the live below ground.  Without the important nutrient cycling which occurs on top of the soil, the forest would have little food and hence little life.

Underground – There is also an underground layer to the forest where roots compete and worms and moles churn through the soil.  Badgers and other mammals dig their dens into this layer.

Forests are busy places which are always active, day and night, all year round.  They are complex and intricate, they are inspiring and captivating.  As we’ll see over the next few days, forests are integral to our culture as well as our survival.  They are places of solitude, places of fear, places of restoration and places to hide.

Tree relationships

“Old growth forests like Broceliande, whether enchanted or not, are complex, diverse ecosystems which seem to embody the idea of balance and harmony”
– Sharon Blackie

Trees, even those to appear to stand solitary, are never alone.  They are a hive of activity filled with a city of residents and passers through.  There are birds, mammals, insects and fungi, all of whom have intricate, intimate relationships with that tree.

Trees have mutualistic relationships with bacteria, fungi and animals.  Trees orchestrate other lifeforms and shape the very environment they live in.

For the birds, the tree is a source of food, a shelter, a place to raise your young and a nursery and play area.  For mammals, the tree can be sanctuary, a place to hide from the rain.  For insects, the tree is pollen and leaves, as well as home.  For fungi, the tree is part of an amazing web.

This amazing, hidden connection is fascinating.  Trees and fungi have a symbiotic relationship where the fungi connects the trees together.  The trees can then use the fungi to direct resources from thriving trees to those which are more vulnerable, especially in the case of related plants.  This underground web turns a collection of trees into a complex super organism which maximises resources and allows for communication between certain species.  For example, pines can transfer carbon to other pines.


These fungi mats are the largest biological entities in the world and some cover 20,000 acres.  They surround and penetrate the roots of grasses, shrubs and trees.  They expand the absorption zone 10-100 times and help plants in their quest for water.  Their work also increases the holding capacity for the soil.  Without them, disease increases, diversity of insects, birds, mammals and plants decreases, humidity falls and the now exposed soils blow away causing desertification.

The paradox of competition and cooperation

Despite playing such an important and cooperative role to so many species, trees spend their entire life in competition.  They are competing with other trees and other plants for water, nutrients, light and space.  And whilst they are doing this, they are also battling the cold, the heat, drought and floor, toxins, parasites and predators.

To cope with these challenges, over time they have developed more and more elaborate ways of surviving and reproducing.  For example, for every one of the 750 species of fig, there is a specialist wasp to pollinate it.  Evergreen trees have needle shaped leaves with a waxy layer to reduce the amount of water loss in the winter.  Deciduous trees drop their leaves for the same reason.

Whilst I’ve only looked at the forest ecosystem from a trees perspective, and haven’t even covered that comprehensively, I hope you can see that a tree is not simply a tree.  A tree is a complex web of relationships and interactions, and a forest is a megacity of organisms, some working together, some competing.  It’s easy to think that a forest is just a group of trees but this is far from the case.