The Amazon Carbon Sink remains a mystery – feedbacks and landscape transformation

Recently, Brienen et al. 2015 published results from different long-term projects on Amazon forest dynamics, showing a generalized decline of the biomass carbon sink. While more than a decade ago, Betts et al. 2004 modelled the so-called die-back of the Amazonia, recent models have been showing an increase of the biomass carbon sink well into the 21st century due to CO2 fertilisation (for example Huntingford 2013). Brienen et al 2015 now argue a decline in the capacity of the carbon sink, caused by an accelerated tree life cycle, increasing the biomass mortality. The carbon uptake is simply getting oversaturated due to the high atmospheric CO2 concentrations. Will the new-generation models show a return of the die-back theory?  As yet, no effect of CO2 fertilisation or accelerated tree life cycles have been found in tree ring studies, such as done by Van der Sleen 2015.

Simultaneously, Haddad et al. 2015 published another study from long-term projects on world-wide forest dynamics. They show fragmentation has long-lasting impacts on biodiversity, nutrient cycling and ecosystem services. They furthermore state that currently more than 70% of the remaining forests are within a single kilometre from its edge and thus severely fragmented! The tropical forest around the Amazon is one of the two regions with a relatively contiguous area. Nevertheless, the fragmentation of the Amazon still results in a considerable carbon loss of approximately 10% of the total, according to Pütz et al. 2014.

The decline of the biomass carbon sink and the effects of encroaching human-transformed landscapes, including fragmentation, show dire consequences of declining ecosystem services potential and conservation value. The two processes might have a coupled effect, decreasing the total carbon storage of the tropical forests. Can this have consequences for the Payment for Ecosystem Services?

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