What Is a Forest? Describing Our Most Important Ecosystems

Photo: CC0 / Pixabay / Free-Photos

Forest ecosystems play an huge role in our planet’s well-being, absorbing carbon emissions and producing oxygen. But what is a forest exactly? We’ll define forests here, discuss their different forms, and finally explain why they’re so important.

You might think a forest is simply a group of trees – but it’s not that simple! So what is a forest?

A deciduous, coniferous, or mixed forest is home to different kinds of trees, as well as other plants, animals, and fungi. Furthermore, there are various approaches even to just defining a forest ecosystem.

Definitions – Agriculture or Ecosystem?

Fall Autumn Trees
The changing colors of the leaves make forests so beautiful in the fall. (Photo: CC0 / Pixabay / Minka2507)

The Food and Agriculture Organization of the United Nations (FAO) defines a forest as a collection of trees covering at least 0.5 hectares. The crowns of the trees must cover at least ten percent of the underlying soil. When fully grown, the trees must be at least five meters high. Some agricultural (i.e. man-made) forest forms are included in this definition – others are not.

The ecological definition takes a different perspective. A collection of trees is not considered a forest until it forms its own characteristic ecosystem. Each ecosystem has special conditions that distinguish it from the unforested environment:

  • Forest temperatures are more balanced: Cooler in summer and warmer in winter than surrounding areas. In summer, trees ‘consume’ a large part of the sun’s energy through photosynthesis, making its forests a few degrees cooler. Trees and soil also store a lot of water – when it evaporates, it also cools the air. In winter, on the other hand, forests ensure that the heat emitted by the ground is not lost.
  • It is less windy inside the forest than outside, because the trees and other plants form a natural windbreak.
  • Humidity in is slightly higher than in surrounding areas. This is because water evaporates from the leaves of the trees and other plants, with much of the moisture remaining below the canopy.
  • The leaf canopy controls the light levels.

You’ll probably notice all these things yourself if you spend time in the great outdoors. But they don’t just appear out of nowhere, and the monocultures planted by humankind rarely have a truly balanced ecosystem. What makes a natural forest so diverse and so important?

How Do Forests Grow?

Savannah Tree
Savannahs will form in regions without enough regular rainfall for forests to grow. (Photo: CC0 / Pixabay / Ron BD)

Forests don’t grow everywhere on earth. For an ecosystem this complex to develop, certain conditions must be met:

  • There must be a minimum amount of annual precipitation. Depending on the temperatures and the type of trees, this amount of rain and snow can vary. If there is not enough rainfall, savannahs or steppes form instead.
  • Trees need minimum temperatures to grow and be able to photosynthesize. The period of a year in which temperatures are sufficient is called the growing season or vegetation period. Studies have shown that at least 5°C (40°F) on average per day must prevail near the ground for trees to grow. This is why there are no forests above certain altitudes and in polar regions.

Of course, many parts of the world have these conditions in abundance – according to the WWF, forests cover about 30 percent of the land areas worldwide. And there’s more life – and more variety and complexity – in a forest than just trees!

Biodiversity – Different Types and Multiple Layers

Moss Tree Stump
Trees aren’t the only forest inhabitants – mosses and fungi play an important role. (Photo: CC0 / Pixabay / Woong Hoe)

Trees are naturally the first thing that comes to mind when we think of forests. However, these imposing plants, with their crowns, branches and trunks, form only the uppermost layer of the forest ecosystem. The three layers underneath are, firstly, shrubs and other bushy plants; then mosses, weeds, and grasses; and finally the forest floor, with the trees’ root systems.

Each layer is home to different animals, plants and fungi, which all contribute to the functioning of the ecosystem. In a naturally growing forest, it’s not just the living plants which are an important food source for many animals (which in turn are part of the food chain). Dead vegetation is decomposed by fungi, bacteria, and small animals like earthworms. For this reason, these lifeforms are also called ‘decomposers’. They return nutrients to the soil, continuing the natural cycle.

Coniferous, Deciduous, and Mixed Forests

Conifers Forest
We have created so many non-diverse monocultures like this coniferous forest. (Photo: CC0 / Pixabay / J. Plenio)

The four layers also differ depending on which trees dominate a region. In general, botanists distinguish between coniferous (or softwood), deciduous (or hardwood), and mixed forests, with different distributions throughout America’s 800 million acres of forest.

The most familiar coniferous trees are spruces and pines, which mostly grow in the Rockies, the Pacific West and around the Great Lakes. Spruces are popular in commercial logging because they grow fast and their wood is versatile. Consequently, many softwood forests are artificially afforested, with trees so densely-packed that little light gets through. For this reason, there is comparatively little undergrowth and the biodiversity in these ecosystems is lower than elsewhere.

Deciduous, or hardwood, trees like oak and maple grow widely throughout the Eastern and Midwestern states – although between 1600 and 1900 half of the forests on the Eastern seaboard were destroyed! Hardwood forests are very diverse: Because the trees are bare in winter and leafy in summer, different amounts of light can penetrate the canopy. In spring, for example, the bare trees allow enough sunlight to pass through for early blossoming plants to flourish.

Mixed forests are particularly widespread in the South and Southeast. They can better withstand fires, drought, storms, and pests than purely deciduous or coniferous trees. In addition, this form of ecosystem allows for a particularly large diversity of species.

Why Are Forests So Important?

Green Leaves
If we look after nature, nature will look after us. (Photo: CC0 / Pixabay / Paul Steuber)

After the oceans, forests have the greatest influence on our climate. They are, first and foremost, huge carbon reservoirs. It’s difficult to say whether they tend to cool or warm the atmosphere, as different processes counteract each other.

  • They cool the atmosphere by evaporating water and by converting solar energy in photosynthesis.
  • On the other hand, trees mean that the earth absorbs more sunlight, rather than reflecting it.

However, the huge importance of of forests for our planet goes beyond their influence on the climate. In addition, they have other important functions:

  • They provide a habitat for millions of animal and plant species. Forests are home to 80 percent of the earth’s terrestrial biodiversity. We are only beginning to understand the role natural biodiversity plays in regulating complex ecosystems.
  • During heavy rainfall, trees and the forest floor absorb a large part of the water. In this way, forests prevent floods from forming after heavy rainfall. They also protect against erosion, landslides, and avalanches in mountainous regions.
  • More than just the air we breathe – which we can all agree is pretty important – forests also provide endless resources to human communities around the world. According to the WWF, 1.6 billion people are directly dependent on them to survive.

Forests are important to our way of life and to the future of the planet. Sadly, deforestation is still a huge problem, thanks to our consumption of products like palm oil or practices such as illegal logging. Fortunately, many governments and NGOs like the WWF are working towards more sustainable practices such as reforestation.

This article was translated from German by Will Tayler. You can read the original here: Ökosystem Wald: Das macht Laub-, Misch- und Nadelwälder aus

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