Why Do Forests Have High Biodiversity?

Forests are awe inspiring habitats, don’t you think?

Stepping into a forest is like stepping into an entire world of unique plants, trees & animals all co-existing together in sensitive ecological relationships.

For this reason, forests make major contributions to our earth’s overall species, and it’s fascinating to understand why forests have such high biodiversity.

Biodiversity is caused by having the widest variety of ideal growing conditions to support the greatest variety of different species in an environment.

So why do forests have high biodiversity?

Forests have high biodiversity because the vertical growing surface and resulting canopy shade creates micro-niches by altering locally available light, heat & moisture.

For example: When a tree falls in the forest, it opens up a gap in the canopy that allows extra light & warmth to penetrate an isolated area of the landscape.

Notice the hole in the canopy of this forest:

This might seem like a subtle observation, but it actually gets right to the core of why forests are such hot-spots for species diversity.

Once you know how to look at forests in terms of micro-niches, it’s possible to track biodiversity by studying high level forest patterns associated with diverse growing conditions.

Forests Are Bursting With Micro-Niches!

A micro-niche is a small patch of ideal growing conditions for specialist plants & animals, caused by localized differences in sunlight, temperature & moisture.

It’s just like how some plants need full sun, while others grow better in partial shade.

The more variety of diverse growing conditions you have in a small space, the more diversity of species can co-exist. It’s that simple!

Diversity in growing conditions can be described as:

• Shady places contrasting with sunny places
• Warm places contrasting with cool places
• Wet places contrasting with dry places

So what causes such a variety of diverse growing conditions to show up in forests? Of course it’s the trees!

So let’s talk about how trees play into all this…

How Do Trees Increase Biodiversity?

Trees increase biodiversity because they moderate the extremes of climate making it possible for more sensitive species to survive.

Some of the biodiversity benefits provided by trees include:

1. Trees cast shade which moderates the ground temperature and reduces evaporation.
2. Trees provide a vertical growing surface for vines, mosses, fungi & lichens.
3. Trees protect the soil against harsh summer sun and pounding wind/rains.
4. Trees periodically drop leaves which help to structure the soil & cycle nutrients while creating habitat for soil organisms.

These benefits all occur to varying degrees depending on the type, size & age of the trees growing.

The result is that forests create a nearly endless spectrum of different growing conditions to suit the individual needs of various plants & animals, with the most important benefit being climate moderation.

Climate Moderation By Forests Increases Biodiversity

Forests moderate the climate by providing a natural filter between the harsh sun, wind & pounding rains to the sensitive soil organisms & plants at the surface.

Climate moderation effects produced by forests include:

• Forests are cooler during summer
• Wind effects are reduced
• Evaporation is reduced
• Soil drainage & water infiltration is improved

These factors all help to extend the growing season during heat & draught, while reducing overall vulnerability to extreme fires, floods & insect imbalances that are common in stressed environments.

Inside the forest is like a nursery for plants and animals that would otherwise be unable to stand the unfiltered sun, heat, draughts, floods & strong winds.

If the trees are cut down however, the sun-blocking & moisture holding capacities of the forest canopy dries up.

Suddenly a landscape that was once lush & fertile becomes dry and crusty, susceptible to erosion, fires, flooding and unable to support the original ecology.

This effect is called desertification, and it happens all around the world when forests are not tended in sustainable ways.

The result of desertification is an extreme loss of biodiversity including plants, trees, insects, amphibians, vines, fungi, and countless micro-organisms.

Forests Reverse Desertification

Desertification is one of the main causes of biodiversity loss on our planet.

This is the gradual transition of lands that were once lush and fertile into land that can no longer hold enough water to support historical species.

As desertification gradually replaces ancient forests with drylands, we lose the benefits of cooling, moisture retention & climate moderation, causing a loss of biodiversity & reduced stability of the environment.

In case you’re wondering what we can do about this, Permaculture has shown that it is possible to re-establish permanent forests in land that was once considered too far gone, as shown in the following documentary.

Of course, deserts do have their own contributions to biodiversity in the form of lizards, snakes & succulent heat hardy species, but it’s all a matter of balance.

By planting forests, we can reverse the trend of increasing desertification and return stability to the local climate while improving quality of life for people living in these regions.

Beyond Climate Moderation…

Aside from the major climate moderation benefits of forests, there are also several other factors to observe and consider with regards to biodiversity in forests.

Let’s cover these in the next three points.

#1 Forests Have Vertical Growing Surfaces

It’s interesting to note that forests have entire growing surfaces that simply don’t occur in prairies, fields, deserts & wetlands.

Unforested landscapes (lacking a closed canopy) have their total growing surface limited to low growing plants and the root zone.

Forests however, provide a 3 dimensional growing surface that is home to thousands of specialized birds, animals, plants, insects & micro-organisms.

These layers include things like:

• Herb layer
• Shrub layer
• Root layer
• Canopy layer
• Fungal layer
• Vines
• Bark layer (lichens, mosses & arboreal ferns)

Each unique layer provides it’s own little micro-niche in the overall ecosystem.

Forest layers are very simple to observe, and they each represent a unique opportunity for biodiversity to present itself.

#2 Forests Have Multiple Stages Of Succession

Another important contributor to biodiversity is the fact that forests go through multiple stages of succession.

It’s very common (and quite natural) for forests to go periodic disturbances like fires or hurricanes that interrupt the life cycles of some species, while creating new opportunities for others.

This might sound like a destructive thing, but it actually increases the net biodiversity because each stage of forest succession has it’s own unique community of plants, trees & animals.

Forest succession can be classified broadly into 4 stages:

1. Disturbed landscape (after fire, hurricanes, clearcutting, etc)
2. Regenerating fields
3. Second growth forest
4. Old growth forest

I covered this topic in much greater depth in my article on how forests form, so go check that out if you want to learn more about forest succession.

The important thing for our discussion on biodiversity is that a forest including all four of these stages will have much higher biodiversity than an environment made of one isolated stage alone.

#3 Not All Forests Have High Biodiversity

With all this said, I think it’s important to mention that not all forests do have extremely high biodiversity.

Some forests like human planted monocultures develop with relatively low biodiversity compared to the natural forests that evolved over hundreds or thousands of years.

This is because many forests are managed for specific economic species, without necessarily designing for the less obvious species lacking direct economic value like fungi, small mammals & birds.

Biodiversity is also a relative measurement that looks at the total number of different species in relation to the total size (area) of a landscape.

(Biodiversity Equals Total Species Divided By Total Area)

But forests are still just one type of ecology and by definition, prairie species, wetland species & desert species will not typically grow inside a forest.

This means that maximum planetary biodiversity depends on the careful management of every possible ecosystem including:

• Forests
• Prairies
• Deserts
• Fresh & Saltwater Wetlands
• Regenerating Disturbed Landscape
• Human planted ecosystems
• Marine habitats (coral reefs, tidal zones, etc)

Each individual habitat has it’s own unique plant & animal communities that add to the overall pool of biodiversity.

Keep Studying Forests & Biodiversity!

As you can see, biodiversity in forests is a huge topic with many contributing factors to consider.

We can’t possibly hope to cover it all in a single article, but I hope this reading has inspired you to look a bit closer and appreciate your local forests.

If you want to learn more, go check out my video tutorial on How To Read The Secrets of A Forest.

Have fun out there & say hi to the trees for me!