Written by Eva Hamrud, PhD
September 1, 2021
18 min read
Topic Review: Forests
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INTRODUCTION
Forests are commonly understood as groups of trees. Or to be more specific, and according to the Food and Agriculture Organization (FAO), they are a patch of land of at least 0.5 hectares covered by trees that are larger than 5 meters high. That’s a rather plain and laconic definition, but reality tells us that forests are much more than a bunch of trees.
Forests host some of our planet’s most incredible biodiversity. In fact, forests are home to 80% of the world’s land-based plants and animals. That includes humans, of course. Millions of indigenous people are almost completely dependent on forests to survive. For many rural communities, forests provide essential resources and support jobs as well. Urbanites depend on them too, though, as forests are the origin of everyday products such as paper, medicines and detergents. On top of that, forests fight climate change, clean the air and protect us from natural disasters. Not to mention that they are an exceptional space to have fun, live adventures or get inspired. Forests are indeed intrinsically bound to our culture and our heritage.
Even though forests are crucial for our quality of life, we lose hundreds of thousands of hectares of forest areas every year. Wildfires, extreme weather events, diseases and human activity affect forests and decrease their area across the globe, in a process called deforestation. Of course, deforestation dramatically reduces the benefits we obtain from forests, causing loss of biodiversity and extinction, displacement of human populations, loss of economic and social resources and desertification, and contributing to climate change.
Given the importance of forests for our lives and wellbeing, this month we asked experts to share all the facts on them. Is global deforestation on the rise? Can we use the resources we get from forests in a more sustainable way? Can we fight climate change by planting trees? Here’s what they told us.
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META-INDEX
Numbers
1/3 area of our planet covered by forests.
10,000,000 hectares of forest lost every year (from 2015 to 2020).
20% percentage of global forest area that is currently under some form of legal protection.
0.52 hectares of forest per person globally.
10% percentage of tree species threatened by extinction.
3,300,000 hectares of forest replanted every year.
73% percentage of forests under public ownership (in 2015).
350,000,000 people around the world that live within or near a forest.
ORIGIN STORY
The Black Dragon Fire
Let’s start by going back to what many consider the largest wildfire in History, which had huge environmental and economic consequences and with which we can learn about common key factors that control forest fires. In the Daxinganling Prefecture of China, the coniferous Da Hinggan Forests used to cover 500 miles long and 300 miles wide, bisected by the Black Dragon river (natural border between China and Russia). The Spring of 1987, however, was one of the driest and hottest of the last years and many parts of the forest were filled with parched vegetation. Trees were not particularly abundant in some areas – they had been cut down and so weeds grew instead. The regional government was not very keen on regrowing such areas of the forest so they just sent workers over to merely remove sun-scorched vegetation. That day, when one of those workers was using his brush cutter, a bit of gas spilled and set fire. Wind was blowing strong. The rest is History.
‘The Black Dragon fire’, which kicked off on May 6, 1987, is considered one of the largest natural disasters of the 20th century. It was not until June 2 (when some rain started to fall) that the fire could be controlled. By that time, 7.3 million hectares had burned, 211 people had died, 266 more were injured, and 50,000 had become homeless. Of course, the event was a tremendous hit to the Chinese economy, with total damage estimated at more than $4 billion – including the loss of almost a sixth of China’s timber reserves.
The Black Dragon fire affected not only China but also Russia. However, their response was very different. While China sent over 60,000 people to fight the fire trying to protect one of its main timber reserves and to avoid desertification (Gobi’s desert is pretty close, check a map!), Russia basically let it burn. The reason? With 815 million hectares of forests (20% of the worldwide forest surface), Russia was not too worried about losing some of them (indeed, they lost almost 5 million hectares). Yet, Russia forgot about a consequence that many at the time failed to acknowledge. The Black Dragon fire increased the tropospheric levels of ozone and sent a huge amount of contaminant particles over Russia, China and the North Pacific Ocean, which had knock-on effects on human health and ecosystems. Of course, biodiversity was greatly affected in both countries and, even today, some areas are still in recovery.
This episode is probably a good example of how people, economy and environment can all be affected by a wildfire, and of how much the governments can do to avoid such negative effects. For Hinggan forest and its people, it could still take several generations to go back to normal – if this ever happens.
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BACKGROUND
Is global deforestation decreasing?
Read the full answers to this question here. The truth is, the jury is still out on this. “Although this question is all about quantification and we already have the required tools (i.e. satellite imagery and remote sensing algorithms) to quantify, it is a complex question,” admits Dr Ralph Trancoso from the University of Queensland. One of the reasons is the lack of consensus on just what “deforestation” really means. For Dr Trancoso, “there are several types of “deforestation”, such as forest clearing, selective logging, or even a single tree removal. Trees can also be killed by bushfires, for instance.” Exactly what each study considers a forest, and which years they take as a baseline, are also important things to consider. “Different regions adopt different definitions and methods for deforestation monitoring, which makes the integration of figures challenging at global scale,” Dr Trancoso adds. Yet, he concludes that global deforestation seems to be declining – at least according to this recent paper and to the Food and Agriculture Organization.
Prof Robin Chazdon, from the University of the Sunshine Coast, agrees. She writes that “the most recent Forest Resources Assessment by FAO in 2015 reported that global annual rates of net forest loss declined from 7.3 million hectares/year in the 1990s to 3.3 million hectares/year between 2010 and 2015.” However, Prof Chazdon also warns about the complexity of these measurements and the potential misinterpretation of the data if we aren’t careful. There is also more to deforestation than the size of the area lost. She regrets that “forest quality is often omitted in deforestation and reforestation statistics.” Prof Chazon claims that forest degradation, which these deforestation measurements fail to quantify, “has severe consequences for global carbon emissions and for regional conservation of plant and animal populations.”
Not everyone agrees that deforestation is decreasing, though. Dr Jean-François Exbrayat, from Edinburgh University and Prof Jennifer Swenson from Duke University both highlight that deforestation measured seems to be increasing – at least when you measure it by tree cover loss (a slightly different metric). Dr Exbrayat also indicates that “deforestation has very different regional dynamics” and writes that although “Brazilian deforestation began to drop in 2005, […] there’s been a slight increase in the last couple of years”. That’s also true for Indonesia, he explains, where “deforestation has increased steadily in the last 15 years with conversion from natural forests to oil palm plantations.” Differences could arise across different types of forests, too. Prof Lars Hein from Wageningen University explains that “boreal forest cover may be gradually increasing.” He explains that this could be related to climate change, “which permits forests to expand to higher latitudes.” In Europe, “temperate forest cover is stable or perhaps slowly increasing” says Prof Hein. However, he also warns that tropical deforestation continues unstoppable.
If you’re curious about this and want to see whether forests have shrunk or expanded in your region in recent years, Prof Jennifer Swenson recommends this site. She warns that “this dataset does not map degradation of forests, which is an enormous issue,” so keep that in mind. And one final thing: even if the rate of destruction is reduced in a given year, the net loss continues, says Prof Swenson: “every year human activities continue to remove forest that is not replaced by replanting/regrowth (but converted to other uses).”
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THE CONSENSUS
Does planting trees help reduce climate change?
70% Affirmative via 10 experts
Read the full answers to this question here. In the last decade, humankind has planted more than 3 million hectares of trees per year. Although this does not make up for the almost 10 million hectares we lose per year, efforts to avoid deforestation by planting trees and protecting forests are stepping up. However, is this strategy really helpful for fighting climate change?
Prof Bill Laurance, from James Cook University is certain: “Absolutely. Trees store lots of carbon, thereby slowing climate change, and they emit large amounts of water vapor into the atmosphere, which cools the land via evaporation.” Prof John D. Bailey from Oregon State University agrees: “climate change is closely tied to the concentration of carbon dioxide in the atmosphere, and trees remove carbon dioxide from the air as they photosynthesize and grow.” Not all trees are the same, however, and their capacity to store carbon changes throughout their lives: “slowly at first when young, then rapidly during middle age with maximal height, […] then slowing down again as they get really old,” he explains. This is why, according to J. Rodrigo Garcia del Campo from the Spanish Biotechnology Centre, the tropics are the best area for tree planting as “trees grow fastest there and thus trap more CO2.”
Anything else we should be taking into account? Prof Mark Huxham from Napier University warns against indiscriminate tree planting because “we need to be careful about where we plant and what species we use.” For example, “planting exotic pine species on peat bogs in the Scottish Highlands […] tends to reduce biodiversity and actually release carbon, since it leads to the drying out of the peat,” he explains. In this line, Dr Paul Hessburg from the US Forest Service advises: “Where forests have been lost to wildfires and they will still grow under locally changing climatic conditions, replanting trees makes sense”. This is also true for “areas where forest land was cleared for agriculture or other uses and later abandoned,” he adds. Garcia del Campo warns that “planting trees in an area where previously there was grass or was covered with snow, could locally increase the temperature” in the area, thus contributing to global warming through the so-called albedo effect. He also stresses that tree planting is no magic bullet by itself: “planting trees as a compensatory measure is not an authorization to continue polluting: if the use of fossil fuels is not reduced and deforestation is limited, climate change will not reverse.”
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THE CONSENSUS
Are wildfires becoming more frequent?
83% Affirmative via 12 experts
Read the full answers to this question here. A wildfire is defined as an uncontrolled fire that burns through wildland vegetation, often in rural areas. It can be caused by human activity (farmers clearing fields, equipment generating sparks…) or by natural causes (lightning, volcanic eruption…) Now, some fear that the drier and more arid weather that global warming is bringing to some areas may increase wildfires.
Prof Hein indicates that at a global scale, wildfires are more frequent now due to the fact that “dryland ecosystems are experiencing more frequent and severe periods of drought.” This is indeed a consequence of climate change, “which makes the soil moisture evaporate and make climates drier and more arid making vegetation more flammable,” explains Garcia del Campo. A similar view is shared by Matthew Harris from Keele University who, citing the recent IPCC’s 6th assessment report, reminds us that “the frequency and severity of wildfires, and fire [favourable] weather as a whole, is set to increase as the planet warms to 1.5ºC above the pre-industrial average.” It can get scarier, as Harris warns that “if the planet warms to 2ºC above the pre-industrial average, the likelihood of increased wildfires becomes even greater.” We must remember, he stresses, that “wildfires are a positive feedback loop – fires emit carbon dioxide, thereby worsening global warming, and in turn increasing the frequency and severity of fire weather.”
Prof Bailey claims that not only the frequency of wildfires but other parameters such as “area burned by wildfires, the average sizes of wildfires, the amount of effort and expense it takes to fight them, and the area that burns at high intensity” are also worsening. Prof Bailey, also blames climate change, which “has created longer fire seasons globally, higher temperatures, drier fuels and conditions that favor high-intensity wildfire.” There are other factors, however. “Management and harvesting on public lands in western US has really slowed and, together with fire exclusion in these forests, we’ve had decades of steady fuel accumulation in overly-dense, carbon-rich, high-biomass forests,” says Prof Bailey.
Dr Alexander Lees from Manchester Metropolitan University points out that “areas which have been historically unaffected by wildfires – e.g. undisturbed Amazonian forests, are now suffering from them for the first time.” However, he also highlights that wildfire frequency changes in different regions over the centuries. This is something that Dr Colin Beale from the University of York agrees with. “Across most of the African savannahs where our ancestors have been lighting fires for longer than our own species has existed, fire frequency today is lower, as a consequence of land conversion and high grazing pressure removing fuel to support fires.”
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THE CONSENSUS
Can logging be made sustainable?
Read the full answers to this question here. As we said from the very beginning, forests are not only a bunch of trees but also a source of essential resources and the origin of everyday products such as paper, medicines and detergents. Logging, where we cut down trees to use their wood, obviously harms forests but is necessary for human beings. Indeed, as Prof Bailey writes, “wood is a wonderful, renewable material for many of our society’s needs; it holds many advantages relative to metals, concrete and plastics from the perspective of carbon/climate, as an alternative to mining ores and minerals and fossil fuels (all non-renewable on our finite planet).” The question is then, can we make this activity sustainable so we can keep getting what we need from forests without damaging them?
For Garcia del Campo, sustainable logging is not impossible. In general terms, “if the plant biomass is extracted in a period of time that allows the system to generate an amount similar to that extracted, the process will be sustainable.” Easier said than done, however. How to achieve it? Dr Camille Stevens-Rumann from Colorado State University gives some ideas, explaining that “logging can be done in such a rotation that it is not as environmentally destructive” and harvesting non-native species may help control invading species. Prof Hein mentions the so-called ‘selective logging*’*, “where commercial species are harvested but sufficient large trees are protected in order to produce seeds that allow for maintaining the large majority of biodiversity and carbon retained in the forests.”
Prof David Lindenmayer from Australian National University warns that sustainable logging requires thinking about the specific ecosystem we’re looking at. “Systems that are subject to widespread recurrent wildfire and already heavily modified by humans are often places where there should be no logging to allow recovery.” As Prof Bailey puts it, “trees grow, and they grow well when managed and can fit into any sustainable conservation plan… and can meet many of the needs of society in the process.”
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QUICK ANSWERS WITH CONSENSUS
Do urban forests improve health? Every expert we asked said yes. Urban forests not only store carbon and provide a habitat for wildlife, they also cool our streets and improve our mental and physical health.
Does soy agriculture contribute to deforestation? Yes. Although much of the soybean planted in the Amazonia has replaced cattle pasture, soy agriculture remains a major driver of forest loss.
Does hazard reduction burning prevent bushfires? No. Hazard reduction burning (also called intentional burning or prescribed fire) will not prevent bushfires, because there will always be some kind of vegetation that can grow and set fire. That said, it does seem to reduce fire intensity and fire damage.
Can wood be recycled? Only non-treated wood can be recycled – but don’t throw them in your usual household recycling bin. Wood is accepted at local recycling centres and wood recycling establishments, which will have the equipment to process it. You can also re-use it, burn it in your fire pit or create mulch or compost. By contrast, finished wood (painted, lacquered etc.) is still not recyclable and can be hazardous, so better take it to a hazardous facility.
Are forests becoming less able to sequester carbon? Although healthy tropical forests are able to capture atmospheric carbon, several recent studies report that their ability is decreasing. In the 90s, tropical forests removed 17% of human-made carbon dioxide emissions. By the 2010s, however, they removed just 6%. The cause seems to be carbon loss from trees dying, which increases as global temperature rises.
TOP ANSWER
Are there forests in the sea?
Mark Huxham: An expert from Napier University in Environmental Science
Yes there are. Mangrove forests consist of woody species (trees and shrubs) that are able to tolerate salinity and other stresses that come from growing in the intertidal zone, so at high tide these forests are indeed in the sea. There are around 70 species of mangrove globally, growing in tropical and sub-tropical zones. Although mangroves make up only 0.7% of the tropical forest cover in the world, they are disproportionately important for nature and for people. They perform many of the same functions as terrestrial forests – such as producing timber, medicines and homes for birds and other fauna. In addition, they act as marine habitats, providing nursery grounds for fish and crustaceans and protecting shorelines from erosion. They are one of the most powerful of all natural carbon sinks, often containing 5 to 10 times the carbon density of terrestrial forests. Most of this carbon is buried in the deep, anoxic soil.
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TAKEAWAYS
- Overall, deforestation rates are probably decreasing, but we are still far from the real objective: zero net deforestation.
- We should also think about forest degradation when assessing the health of our planet’s forests.
- Planting trees helps to fight climate change, but we should take into account the place where we plant them and the species we use. Tree planting alone won’t revert climate change.
- Wildfires are becoming more frequent, longer and more intense. Global warming is one of the reasons behind it.
- Strategies like selective logging or rotation, logging non-native tree species or waiting for the ecosystem to regenerate allow a more sustainable way of logging.
- Hazard reduction burning does not prevent wildfires, but can reduce their intensity and damage.
- Non-treated wood can be recycled, but take it to your local recycling facility. Upcycling is probably best if you’re into DIY!
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