Understanding the carbon sequestration in the mountain dry forest (MDF) situated in the southern part of Ecuador inferred from eddy-covariance measurements

Forests are vital carbon sinks, absorbing and storing large amounts of carbon dioxide (CO₂) through photosynthesis. Thus, forest ecosystems strongly contribute to climate change mitigation inducing a carbon sink function. Whether a forest is acting as a source or sink is highly dependent on the microclimatological conditions of the region in terms of the heat and water budget. Our study area is the mountain dry forest (MDF) on the western flank of the Andes Mountains in southern Ecuador, i.e. the Tumbesian dry forest of the Laipuna Reserve. The climate of the region is characterized by a strong seasonality influenced by the interhemispheric shift of the ITCZ, which result in a distinct dry (June - December) and wet (January - May) season. However, this seasonality can render these ecosystems susceptible to fluctuations in precipitation and temperature patterns, including prolonged drought periods that adversely impact tree regrowth. Consequently, the MDF becomes vulnerable to the effects of climate change. In contrast, the trees in the MDF also exhibit adaptations that enable them to withstand drought conditions, which may feature a higher resilience against climate change.

To understand the driving processes of carbon and water exchanges over the MDF and response to climate change, an eddy covariance flux tower has been installed over the canopy. The tower is equipped with an open-path Irgason system (Campbell Sci. Inc.) to obtain net-ecosystem exchange (NEE) and evapotranspiration (ET) as well as additional meteorological sensors to measure precipitation, net-radiation and soil conditions. Additionally, soil CO₂ efflux measurements are used to estimate the below-ground carbon exchange and its contribution to the total above-canopy signal.

Our main focus is on the quantification of the carbon storage capacity and its variations according to the clearly pronounced seasonality. Further, since water scarcity and heat stress impact the carbon sequestration, we also aim to analyze climate stress situations and its effect on the carbon exchange. For this, NEE is partitioned into GPP (Gross Primary Productivity) and Reco (Ecosystem Respiration) to get insight into carbon uptake by photosynthesis and carbon release by respiration. The preliminary results of the study show that during the wet season the ecosystem generally acts as a carbon sink (GPP = 188 gCm^-2month^-1, Reco = 155 gCm^-2month^-1), while during the dry season it oscillates around neutrality. However, considering the transition periods, a stronger dependency to the climate conditions can be observed, which creates alternating patterns of carbon sink and sources.