2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
An international team of biologists has conducted a large-scale study of large forests on Earth and determined how the living biomass of a forest is distributed among trees of different sizes and types. It turned out that exactly half of all biomass is contained in only one percent of the largest trees, most of which are more than 60 centimeters in diameter, scientists report in an article in Global Ecology and Biogeography.
Forests take the most active part in the carbon cycle on our planet: respiration, photosynthesis and gas exchange in trees determine the rate and mechanisms of the processes of conversion and transfer of carbon on Earth, and, accordingly, their effect on the global climate. At the same time, the living biomass of the forest is a very voluminous storage of carbon, which, under certain conditions, can appear in the atmosphere in the form of carbon dioxide. For example, scientists from NASA recently showed that it was the increase in the number of droughts and fires in tropical forests that led to a noticeable increase in the share of carbon dioxide in the atmosphere in 2015-2016. At the same time, despite a large number of studies devoted to the species diversity and ecological roles of various trees, no systematic analysis of trends in the distribution of biomass between trees of different species and its relationship with the size of trees, common for all forests, has been carried out to date.
To fill this gap, an international team of 98 scientists led by James A. Lutz of the University of Utah surveyed 48 large forests around the planet ranging from 2 to 60 hectares and estimated the distribution of forest biomass among trees of different sizes. In total, scientists have studied more than 5.6 million trees with a diameter of more than one centimeter. These trees represented nearly 9.3 thousand different species from 210 families.
Map of the forests explored in the work
It turned out that in different forests the total biomass varies from 13 to 559 kilotons per hectare. At the same time, exactly 50 percent of all forest biomass is contained in the only upper percent of the largest trees (and 41 percent of all living biomass is in plants of a certain size - trees, the diameter of which at human chest level exceeds 60 centimeters). Scientists point out that the size of the largest trees and the total number of large trees in a forest are unambiguously correlated with total biomass, meaning that a forest cannot store a large amount of carbon from small trees alone. At the same time, it is interesting that the greater the living biomass of the forest, the less species diversity in it.
In addition to the general patterns for all forests, scientists also analyzed their geographical distribution. It turned out that with increasing latitude (as in the Northern, Ta and Southern Hemispheres), the total biomass of the top percent of the largest trees decreases, which is associated with a decrease in the total number of large trees. At the same time, the total number of trees in the forest per unit of its area also decreases. In addition, a decrease in the size of trees and a shift in the distribution of biomass when moving away from the equator is accompanied by an increase in the complexity of the forest structure.
Scientists note that their results primarily emphasize the importance of large trees for all forest ecosystems without exception. Despite the fact that the total number of large trees in forests is significantly less than small trees, shrubs and small plants, they represent the most common species and determine the structure of forest ecosystems - by controlling the amount of carbon, water and sunlight in different parts of the forest. Therefore, scientists propose to pay more attention to large trees, both from the point of view of fundamental research (biological, ecological or climatic), and in the development of industrial and technological processes, in particular when planning felling.
While it is difficult to overestimate the impact of rainforest trees on the global climate, sometimes the relationships are not the most obvious. For example, scientists recently discovered that slowing transpiration due to rising concentrations of carbon dioxide in the atmosphere can lead to asymmetries in precipitation changes between the Western and Eastern hemispheres of the Earth.