As climate change intensifies and awareness of carbon reduction grows, while discussions on how to reduce emissions heat up, there's still a fundamental solution: planting trees. Planting trees is a carbon sequestration mechanism, helping us "replant" carbon back into trees or soil, thereby reducing atmospheric CO2. Why does planting trees also create carbon? Which types of trees are most efficient at storing carbon? How can ordinary people incorporate tree planting into their daily lives to avoid becoming carbon producers? The Environmental Information Center interviewed Professor Liu Wanyu of the Department of Forestry at National Chung Hsing University, offering insights into the secrets of trees. She explains how forests not only purify the air and provide a healing atmosphere, but also hold significant value in carbon sequestration.
Trees are the best carbon absorbers
Most people's understanding of "carbon" is limited to carbon dioxide. Excessive air pollution can harm people's quality of life. In fact, in addition to "carbon emissions," nature also has a "carbon sequestration" mechanism that serves to lock carbon in rather than release it. One of the most common ways to sequester carbon is to plant trees.
Liu Wanyu explained that during the growth of saplings, carbon dioxide is converted into organic carbon through photosynthesis and fixed in the tree body. It also releases carbon dioxide by absorbing oxygen to perform "respiration". Photosynthesis is more frequent than respiration, hence the saying that planting trees is equivalent to "planting carbon".
Liu Wanyu explained that every 1.6 tons of carbon dioxide in the air can be converted into 1 metric ton of carbon. A tree can absorb approximately 900 kilograms of carbon dioxide over its lifetime. This converted carbon, over time, accumulates into the familiar wood tissue.
In addition to trees themselves storing carbon from the natural world, the soil beneath the ground also possesses a powerful carbon sequestration capacity. Liu Wanyu explained that soil stores carbon because plants and animals become part of the soil after they die. Plants and animals are organic organisms, and their rich organic matter contains carbon. Therefore, carbon doesn't actually disappear after death; instead, it transforms into organic matter and is stored in the soil.
The carbon stored in trees isn't necessarily permanently fixed, preventing it from being released back into the atmosphere. Liu Wanyu noted that trees can release carbon dioxide back into the atmosphere due to forest fires or logging, and poor health (such as severe pests and diseases) can also reduce a tree's carbon sequestration capacity. Frequent tillage during farming can accelerate the decomposition of organic matter, exposing it to air. The use of fertilizers and pesticides by farmers can also reduce soil organic matter and release greenhouse gases into the atmosphere.
The changes and invariances of carbon
However, she also noted that how felled wood is used also affects the extent of carbon dioxide released back into the atmosphere. "The finer the wood is cut, the more carbon is released," she explained. For example, if most of the tree is preserved to be made into large wooden furniture, the carbon remains trapped within the furniture. Conversely, if the tree is shredded into pulp, much of the carbon dioxide is released back into the atmosphere during the process.
With climate change accelerating, carbon conservation also requires efficiency. Liu Wanyu explains that larger trees can store more carbon. To improve carbon sequestration capacity, a single tree must be cared for "to grow taller, faster, and healthier." Managing a forest plot requires maximizing the combined carbon sequestration capacity of all trees per unit area, emphasizing regular thinning, pruning, and drainage.
However, a tree's carbon absorption capacity isn't constant; it gradually decreases with age. Liu Wanyu explained that international research has shown that younger trees have greater carbon absorption capacity. This is because trees store carbon in their bodies; larger trees have greater carbon reserves. However, like humans, trees stop growing taller and thicker after reaching physiological maturity, and thus can no longer absorb new carbon. Therefore, a tree's carbon absorption efficiency gradually decreases.
"In theory, you have to plant trees, but after they reach a certain stage, they have to be cut down for use." Liu Wanyu pointed out the fact that the carbon benefits of tree planting have their limits. Different tree species have different carbon sequestration capabilities. Liu Wanyu pointed out that, taking Taiwan as an example, the land can basically be divided into two categories: flat land and hillside land. Because of the hot climate, broad-leaved trees are mostly planted on the flat land. The top three broad-leaved trees with the strongest carbon sequestration capacity are Acacia, the rhinoceros beetle's favorite tamarisk, and the common furniture material Taiwan beech. Coniferous trees that grow at medium and high altitudes are, in that order, Taiwan cypress, Cryptomeria japonica, and Chinese fir.
Taiwan's land has strong carbon sink capabilities
She also added that broadleaf trees grow in areas with high temperatures and strong sunlight, so they grow faster than conifers and are more efficient at sequestering carbon. Taiwan, located in the subtropics, has considerable carbon sink potential due to its hot and humid climate and rapid plant growth.
"There are too few trees on Taiwan's plains," observes Liu Wanyu. While Taiwan possesses significant carbon potential from tree planting, much of its land lacks proper management. For example, in European countries, rural areas are often filled with vast expanses of forest. In contrast, Taiwan's rural landscapes are often characterized by "sweet green farmland," with a low percentage of farmland being afforested.
Much of Taiwan's farmland has been abandoned or left fallow, and coastal areas also have significant amounts of wasteland. Liu Wanyu believes that active inventory of idle land and increased afforestation on flat lands should be pursued. This will not only improve ground subsidence, prevent wind and sand, but also reduce air pollution and significantly improve people's quality of life. "As our country becomes more civilized and progressive, flat lands need more trees."
There are also cases where areas on mountains that should be used for tree planting are now being used to grow cold-weather vegetables or fruits. Liu Wanyu reminds us that although they are both "trees," the ecological benefits of fruit trees and those of common afforestation species are significantly different. Fruit trees typically have shallow roots and weaker grip, making them vulnerable to landslides or typhoons. Their soil and water conservation capabilities are also weak. Furthermore, fruit trees are often thinner than afforestation species, and their carbon storage capacity is lower.
The carbon-saving benefits of tree planting are gaining increasing recognition. How can the general public participate in mitigating carbon emissions? Liu Wanyu points out that if you have idle land, you can consider planting trees directly. However, before planting, you should first consider whether the trees have other uses besides carbon sequestration, such as pollution control, landscaping, or future timber sales. Then, choose appropriate tree species based on different altitudes and regions.
Personal carbon neutrality is also a good option. Liu Wanyu pointed out that carbon neutrality services are already available for purchase by the general public. For example, before boarding a flight, one can check the carbon emissions of the flight and then pay the corresponding carbon emission fee on the website or by the service provider. This fee will be used to plant trees, and consumers will receive a certificate afterward.
If the threshold is still too high, embracing "green living" is another relatively easy approach. Liu Wanyu says that simply making small lifestyle changes—for example, prioritizing wood products and furniture made of wood over high-energy-consuming materials—can also contribute to a more environmentally friendly lifestyle by purchasing products with a low carbon footprint.
Source: Environmental Information Center (https://e-info.org.tw/node/236007)
