Just semantics?: CO2 fertilization is a disturbance leading to degradation of tropical forests

The effect of CO₂ fertilization is listed as the main cause of the observed increase in net primary productivity and biomass stocks in “undisturbed” tropical forests. This is generally considered to provide greater resilience to tropical forests against disturbances that cause forest degradation such as extreme droughts and logging. Here, we discuss how this may be conceptually short-sighted, given that these forests are being pushed more quickly to their growth limits compared to a situation if atmospheric CO₂ concentration was not rising. Once this growth limit is reached, this shift — from a phase dominated by the CO₂ fertilization effect to a subsequent state marked by progressive saturation or a decrease in carbon sinks — will potentially render these forests more vulnerable to changing climate and other disturbances. In this presentation we will discuss that, in the long term, CO₂ fertilization is a disturbance that leads to forest degradation, falling within the very definition of degradation, as it is human-caused and leads to transient or long-term deleterious change in forest condition (e.g. carbon storage, forest composition). Such a recognition of the CO₂ fertilization affect as a disturbance causing degradation is politically and scientifically relevant in light of climate policies, such that the responsibility for protecting these forests from climate change and other human interventions is shared with countries other than just those that host these forests.