30 Years of Global Forest Decline

Songwen Hu
Kylie Lin
Juo-Yang Chen
Yu-Chin Chen

The Importance of Forests

With ever-growing concerns surrounding global climate change, it is important that we pay attention to the ways in which the world’s environments have changed across time.

Forests contribute significantly to global biodiversity and climate health. As seen in the chart to the side, they constitute roughly a third of the world’s total land mass.

Moreover, forests are not distributed evenly across the globe. The following treemap provides an overview of how global forest amount is distributed, both by country and by continent:

An important thing to note is that five countries — the Russian Federation, Brazil, Canada, the United States of America, and China — contain over half of the world’s forests.

Over half of the world's forests are in 5 countries:

Forest Decline

As seen in the previous section, forests constitute a large portion of the world. However, the amount of land area covered by forests has been decreasing as far back as 1990, when data was first collected by the Food and Agriculture Organization of the United Nations.

Since 1990, forests have declined by 177,502 hectares.

To provide some perspective, one hectare can contain between 1000-2500 trees. If we take the midpoint of that range, one hectare is roughly 1750 trees.

Assuming each hectare of forest that the world has lost contains about 1750 trees, that means that since 1990, the world has 310,628,500 less trees than it did in 1990. For further reference, 177,502 hectares is slightly more than the size of the United States, which is 174.45 million hectares!

This declining trend is worrying for the future of our environment. Even as far back as 2012, a paper published in Global perspectives on sustainable forest management found that a reduction in the world’s tropical forests can lead to detrimental outcomes such as biodiversity loss and an increase in the greenhouse gas effect. A decline in forest cover must therefore be understood so that it can be addressed.

To better understand global forest decline, there are a few questions that can be asked, which we will address in the following sections:
Where in the world has forest decline occurred? What factors contribute to forest decline?

Where in the world has forest decline occurred?

First, let’s break down the world by continent. As seen in the following dumbbell visualization, South America and Africa saw the greatest decline in forest amount between 1990 and 2020, with 129,480 hectares and 106,162 hectares respectively. There is a slight loss, 2,569, in North America within the 30 years. On the other hand, a forest increase in Europe, Asia and Oceania demonstrates that the restoration of forests has seen more success in those continents.

Forest decrease/increase between 2020 and 1990

We can also break down the world further, by country. To better understand where forest area has grown over time, we can examine the change in forest percentage from 1990 to 2020. In the following visualization, the change in forest percentage for each country in the world, colored by continent.

If we look at the percentages grouped by continent, it can be seen that Europe has seen an overall positive change in forest area from 1990 to 2020, indicating that its forest amount is greater than it was in 1990. Given this information, it may be worth looking into conservation and reforestation efforts undertaken across Europe as they seem to have been successful at warding off forest decline over the past 30 years. One recent initiative in Europe, known as SUPERB , aims to plant 20,000 hectares of trees in France.

On the other hand, and as we have seen before, Africa and South America seemed to have significant negative changes in forest coverage. This time, however, it is possible to hover over the individual bars and see which countries drive that change. Please take the time to explore the following visualization.

What factors might contribute to forest decline?

Now that we're familiar with the scale of deforestation and the countries/continents that have experienced the most severe effects, let's move towards investigating some potential factors related to deforestation. In the following sections, we will explore how natural and human factors are correlated to the global forest decline. More specifically, we'll focus on wildfires and droughts as natural factors, and wood production as a human factor.

Wildfire

Wildfire is a common natural factor that leads to decline of forest coverage. To examine whether it is related to the deforestation of a whole country, we compare the wildfire frequency with the forest cover rate in contries with most forest.

This chart shows how the wildfire affects forest coverage rate in countries with the most forest from 1990 to 2020. The width of the line represents forest area of a country. The red indicates more fires occurred in the last 30 years, while yellow indicates less fires. The vertical position represents the forest coverage rate, from 0.1 to 0.8. The left and right side correspond to the forest coverage rate in 1990 and 2020, respectively. Countries suffering from more wildfires (the red lines) are mostly experiencing a drop in forest coverage rate (negative slope), like Brazil, Australia and Argentina. Countries with less wildfires (the yellow lines) are mostly experiencing an increase in forest coverage rate (positive slope), like the Russian Federation, USA and China.

Drought

To examine whether there is a relationship between deforestation and drought, let's focus on a case study on the United States. We retrieved the public drought dataset from the U.S. Drought Monitor.

From the line chart we can notice that the growth of forests in the States experienced its highest surge in 2010, followed by its biggest decline in 2017. Compared with the patterns of drought over the corresponding timeframes, the drought index (DSCI: 0 means none of the area is in drought, while 500 means all of the area is in exceptional drought) is almost identical at these two key points. The two lines also do not share any consistent peaks and valleys. Therefore, there’s most likely no substantial correlation between droughts and deforestation.

Forest Production

Finally, we'll determine if roundwood production as a human factor correlates with the loss of forest area. The relationship between wood and deforestation are deeply intertwined because wood can be used in many different ways, including wood products, fuelwood, timber, paper, etc. In theory, wood production is a renewable resource, but that is heavily reliant whether it is responsibly managed. Let's see if countries do a good job of that in this section!

This trailed scatterplot plots the forest area on the y-axis and roundwood production on the x-axis, with each country’s history represented by a trail. Brazil, one of the countries with the most forest area, experienced a significant decrease in forest area and an increase in roundwood production over the years from 1990 to 2020. Most of these other countries with the most forest area have not had an increase or decrease in the nation’s forests (except for China). Next, we’ll zoom in and investigate some of the countries with mid-range forest area, as indicated by the red box.

This second trailed scatterplot shows countries with more modest forest areas. Forest area is being doubly-encoded by the y-position and color (darker green means more forest). You can watch an animation of this trailed scatterplot by clicking the right arrow underneath the “year” slider. One observation from the animation is that the majority of dots tend to move towards the bottom right corner of the plot. This trend represents a decrease in forest area and increase in roundwood production. Together with the first graph, we can infer that there is some positive correlation between wood production and deforestation.

Conclusion

In conclusion, this article has shown that deforestation is indeed a severe global issue. There were various visualizations that help quantify the scale of the issue. To further understand the underlying factors of this decrease in forest area, we explored wildfires, droughts, and roundwood production datasets and compared them forest data. Both wildfires and wood production show correlation with forest change, but drought did not displayed any correlation. It is important to distinguish that showing correlation does not equate to causation. However, by inspecting data visually, the data can be easily understood and we can find potential factors for further research.