Biodiversity of our planet is one of the most valuable resources. However, for most places in the world, it's only a small picture of what this variety is. Researchers at the German Integrated Biodiversity Research Center (iDiv) and the University of Martin Luther Halle-Wittenberg (MLU) have now managed to build a map of biodiversity of scattered data showing the number of tree species. With the new map, the researchers were able to find out what drives the global distribution of tree species. The climate has a central role; however, the number of species that can be found in a specific region also depends on the spatial scale of the observation, researchers report in the magazine Nature Ecology and Evolution. The new approach could help to improve global conservation.
Around the world, biodiversity changes dramatically and its defense has become one of the biggest challenges faced by humanity. At the same time, we still know a little about why some biological places are varied while others are poor, and where the most biodiversity places are on Earth. Also, the reasons why some areas are more species rich than others are often unclear: what role are environmental factors such as climate play, and the importance of historical factors such as past ice ages for the biodiversity we observe today? Our knowledge is based on dispersed local surveys and has full gaps; especially in tropical regions, where biodiversity can be particularly high. However, it is impossible to close all gaps by completely inspecting the whole planet.
Satellite images can close some data gaps; for example, when gathering information about forest cover, but these techniques have their limitations. "We do not have to count the trees alone, we also need to identify which species they are," Dr Petr Keil, lead author of the new study explained. "In the tropics, we find hundreds of different tree species in one hectare. We can only identify these on site, so most areas have not been inspected for biological diversity – and they probably will not be. "Keil and co-authored Professor Jonathan Chase are scientists at the German Center for Integrated Biodiversity Research (iDiv) and at Martin Luther Halle-Wittenberg University.
Despite the inconsistent data, Keil and Chase wanted to create a world map of tree species wealth. In a first stage, they summarized over 1,000 tree species lists. These came either from small forest plots inspected in previous studies, or from whole countries. For most countries in the world, it is known which tree species can be found there, but not exactly the place, and it is also unclear whether certain species are rare or common. To be able to calculate the number of tree species for the vast spaces on the map, the researchers developed a statistical model. The reason is that the model combines the inconsistent information available on the plots surveyed with the information at country level and also integrates established data on environmental factors such as climate. The result is a complete map of biodiversity in all the wooded areas in the world.
"It was like a 1000 piece pos that we had only a few pieces of it, and we did not even know what the big picture was," said Jonathan Chase. "With our approach, we were able to calculate the missing pieces and put the puzzle with each other." Using the new method, researchers can calculate the number of tree species for different sizes; nature reserve, country or whole continent. This enabled them to investigate the underlying causes of the variation of tree variety on our planet. Their analysis revealed that climate is the most important factor; The highest number of tree species can be seen in the hot, moist tropics. However, the number of tree species also varies across different places with a climate, in some cases quite substantial. In southern China, for example, researchers see a much higher variety than in other regions with a similar climate.
Importantly, however, only the amount of extra variety & # 39; Finding in places like China depends on the viewer's view. "If you're in a forest counting the number of species you can not even notice the difference between China and similar climatic areas. However, when you & # 39; moving from one site to the next and add-on species across several sites, the difference ends, "says Jonathan Chase.
This inconsistency is called neighboring areas into beta diversity. Within a larger region, it leads to a very high variety. Keil and Chase have shown in their analysis that this measure of diversity is particularly high in the dry (non-wet) tropics, especially in mountainous areas such as South China, Mexico, or the Ethiopian uplands. One reason for this high diversity beta would be geological past events, such as ice ages. "During the last glacier, the trees could survive only in mountain valleys, and different populations were isolated from each other," explained Petr Keil. "If you are standing in one of these valleys today, you will see a common number of tree species. But if you climb over the ridge and walk down to the valley Nearby you will find different species of trees, and others in the next valley. "
Keil and Chase are primarily about understanding how biodiversity is distributed on the planet and what factors it sends. But their model can also be useful for developing strategies for conservation, especially in forests where people are not influenced by a variety of trees. For example, in the case of the mountains of China, defending one valley is not enough; Here is the variety of different valleys that give a high biological value to this area. "In order to understand and safeguard biodiversity in reality, we have to look at a local and regional scale at the same time," said Keil. "That is, we need a perspective of a forester who looks in a forest and a big picture of a whole country. Our approach now allows that."