Editor’s Choice: Volume 109 Issue 8

The Editor’s Choice for our August issue is “The fate and transit time of carbon in a tropical forest” by Carlos A. Sierra, Lina M. Estupinan-Suarez, & Ingrid Chanca.

This research article provides an estimate of the transit time distribution of carbon in a Colombian tropical forest ecosystem using a data assimilation technique to parameterise a dynamic ecosystem model.

Tropical forests fix large quantities of carbon from the atmosphere every year. However, the fate of this carbon as it travels through ecosystem compartments is poorly understood. In particular, there is a large degree of uncertainty regarding the time carbon spends in an ecosystem before it is respired and returns to the atmosphere as CO2.

This article estimated the fate of carbon (trajectory of photosynthetically fixed carbon through a network of compartments) and its transit time (time it takes carbon to pass through the entire ecosystem, from fixation to respiration) for an old-growth tropical forest located in the foothills of the Andes of Colombia.

Jacaranda copaia (Aubl.) D. Don one of the most relevant species in the old-growth forests in the Porce region of Colombia, according to their abundance, density and dominance. Photograph by Reinaldo Aguilar (CC BY-NC-SA 2.0).

The authors found that the annual photosynthetic carbon flux returns back to the atmosphere at a wide range of time-scales; 50% of this carbon is respired in <0.5 years and 95% is respired in <69 years, with a mean transit time of 11 years. The transit time distribution shows that carbon in ecosystems is respired on a range of time-scales that span decades, but fast metabolic processes in vegetation dominate the return of carbon to the atmosphere.

The transit time distribution integrates multiple ecosystem processes occurring at a wide range of time-scales. It reconciles measurements of the age of respired CO2 with estimates of mean residence time in woody biomass, and provides a new approach to interpret other ecosystem level metrics such as the ratio of net primary production to gross primary production.

Figure 1: Structure of the compartmental model used to fit the available data from the Porce region of Colombia. Arrows represent transfers of carbon among pools (continuous line) or respiratory losses (dashed lines) to the atmosphere. Autotrophic respiration fluxes in dark blue and heterotrophic respiration fluxes in dark red.

This article provides the first estimation of the fate of carbon after photosynthesis, and of the transit time distribution of carbon for a tropical forest ecosystem, using a combination of model data assimilation methods and the theory of time-scales for compartmental dynamical systems.

In comparison with traditional methods that estimate mean residence times in biomass, this research offers a new perspective to integrate multiple ecosystem processes using the age of respired carbon, that is, the transit time distribution, as a unifying concept.

You can read the full Open Access article by Sierra, Estupinan-Suarez, & Chanca here: The fate and transit time of carbon in a tropical forest

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