In recent decades, tree mortality has increased in many forest ecosystems worldwide. Forest researchers stress the importance of better understanding this phenomenon, as its full impact on Earth's ecology remains unclear.
The rise in tree mortality is troubling for local forest ecosystems. As a global phenomenon, however, it has a significant social impact that remains poorly understood.
"We don't currently know whether climate change will lead to the death of 10% or 50% of all trees worldwide," says Associate Professor of Laser Scanning Samuli Junttila of the University of Helsinki.
He was involved in an international group of over 100 forest researchers, reviewing almost 500,000 forest monitoring studies from 89 countries and five continents. The researchers found that the main cause of tree mortality is anthropogenic (human-induced) climate change and its consequences: heat, dry air and soil, forest fires, storms, and increased insect damage and plant diseases.
"Understanding tree mortality is vital in Finland as well, so we can establish national emissions reduction targets grounded in scientific knowledge, and plan for sustainable forest use," notes Junttila.
Maintaining and strengthening the carbon sink provided by trees is among Finland's key climate measures, alongside phasing out fossil fuels. That is why accurate knowledge of tree health is crucial when countries aim to limit global warming to no more than 2°C above pre-industrial levels, as set out in the Paris Agreement.
Trees: dead or alive?
Led by Junttila, the Global Ecosystem Health Observatory group sought to generate accurate data on the state of trees using cutting-edge computer vision methods based on satellite and aerial images.
"We need monitoring periods of at least five years to determine whether a particular tree is dead or alive. In addition to this basic knowledge, it's essential to understand the characteristics of local habitats and possess data on the age, size and species of trees. Only then can we begin to infer how tree mortality is progressing as the climate continues to warm," he says. "The good news is that modern technology already allows much to be done."
In the article, the researchers aimed to identify methods, requirements and data gaps in monitoring tree mortality trends. Advancements in Junttila's own research field - laser scanning - are making tree monitoring increasingly comprehensive. However, field measurements remain essential to verify both the results and the remote sensing methods.
"We have a tremendous amount of expertise in forest surveying in Finland - it's definitely our strength. But more expertise and teaching in forest health are needed. It's an area where increased investment would be especially important in the current situation," he concludes.
Alkuperäinen artikkeli
Towards a global understanding of tree mortality, International Tree Mortality Network , First published: 31 January 2025, https://doi.org/10.1111/nph.20407
