Trees are crucial components of ecosystems as they support biodiversity, help ecosystems function and provide important services, such as supplying food, sequestering carbon and contributing to the water cycle. Conserving tree diversity is thus a conservation priority for the functioning of natural ecosystems, for mitigating the effects of climate change, and for use by human societies across the world. Despite these important roles, many tree species are not adequately protected, have become rare and may even be at risk of disappearing altogether.
In a recent large-scale study, an international team of researchers headed by scientists from Aarhus University in Denmark, has determined the worldwide distribution of more than 46,000 different species of trees, and estimated the extent to which this distribution falls within protected areas. In addition, they have assessed the intensity of human activity in the areas where the trees are found.
In order to do this, the researchers integrated five large databases, each containing millions of records of tree occurrence. They used these data to calculate the distribution of each tree species and then combined the distributions with a global map of the intensity of human activities. Lastly, they used the world database on protected areas (which includes information of more than 200,000 such areas) to map out the levels of protection for each tree species. Their results are published in the Proceedings of the National Academy of Sciences.
The findings highlight the fact that tree species are poorly protected in general, and some have no protection whatsoever. For the 46,752 tree species included in the study, an average of 50 percent of every tree species’ range falls in landscapes that have no protected areas. For 13.6 percent of the species, there is no protection at all, and most of these species have a limited distribution anyway, making them even more vulnerable.
Furthermore, the authors found that only 17 percent of the species considered are not under pressure from human activities. On average, 14.8 percent of the species are exposed to high or very high human pressure, while 68.5 percent are under moderate pressure.
“By compiling millions of registrations collected by researchers and citizens across the world and shared in open databases, we can calculate where it’s most important to preserve and restore natural areas in order to effectively protect biodiversity,” said Josep M. Serra-Diaz, who was previously affiliated with Aarhus University, and who is now an associate professor at AgroParisTech in France.
The researchers not only quantified the threat to tree species on a global scale, but they also suggested how this situation can be improved by means of the ambitious and smart designation of new protected natural areas.
“We did this by calculating the most suitable locations of potential protection areas if we are to safeguard tree species diversity, not only with regard to the coverage of species, but also with regard to their evolutionary and functional differences,” explained lead author Dr. Wen-Yong Guo, who started the work at the Center for Biodiversity Dynamics in a Changing World (BIOCHANGE), but is now affiliated with East China Normal University in Shanghai.
The researchers have based their work on two existing plans for protecting the world’s biodiversity:
The researchers calculate that, following the above two conservation scenarios, protection of the top 17 percent or the top 50 percent of tree priority areas would make a considerable difference in protecting global tree diversity. They find that protecting 17 percent and 50 percent of the high-priority areas for trees would increase the average protected proportion of each tree species’ range to 65.5 percent and 82.6 percent respectively. This would also leave far fewer species (2,151 and 2,010) completely unprotected.
“But taking a broad-brush approach or just designating the most convenient areas, for example uninhabited tundra and desert areas, will not have the desired effect. Based on our calculations in this study, we’ve identified the areas in which nature conservation makes most sense to safeguard global tree diversity. If we’re smart, protecting 17 per cent of land areas would mean that, on average, a tree species will have protected areas in 66 per cent of the landscapes in which it is found, as opposed to the current 50 per cent. With the Half-Earth vision, the proportion would be 83 per cent. Two-thirds of the tree species that are currently unprotected will have protected areas in the landscapes in which they’re found if we reach the 17 per cent target,” explained Jens-Christian Svenning, professor of Biology at Aarhus University and director of BIOCHANGE.
“But in order to achieve this, we have to look at the distribution of all species across the world, and establish protected areas so that they cover the species and their biological functions and evolutionary differences in the best possible way.”