Towards a consistent global picture of tree mortality trends and drivers

Abstract:

Reports of recent increases in rates of tree mortality are becoming increasingly widespread, with good reason to believe that many of these events are linked to climate change. But we currently lack the capability to make consistent global assessments, precluding putting such reports into the context of the wider picture of forest health across the world. Such a large-scale view is crucial, both because the climate-regulation services provided by forests operate at the global scale and because changes in forest function at the local scale are best understood when put in the context of changes elsewhere. The main challenges hindering a globally-consistent assessment of trends in tree mortality are data availability, inconsistencies in the forms of data, and the logistical and collaborative effort needed to assemble and synthesise these data. Here, we present the results from a wide-ranging survey of data sources potentially suitable for assessing tree mortality rates carried out by the International Tree Mortality Network. We then outline some of the challenges, and potential solutions, to combining these data sources into consistent metrics of tree mortality rates. Finally, we propose a community-driven activity to develop the necessary methodological tools and assemble an open global database of tree mortality rates. This effort is one of the core activities of the International Tree Mortality Network, which aims to bring together the global ecological, forestry, remote-sensing and Earth-system science communities to: (1) quantify trends in tree mortality rates globally, (2) attribute the causes of tree mortality and (3) help develop the capability to accurately predict tree mortality trends, in a changing world.