Carbon flux dynamics in montane tropical wet and dry forests: A comparative study in Southern Ecuador

Tropical forests, spanning wet and dry forest ecosystems, are pivotal in regulating the global carbon cycle and climate through dynamic exchanges of energy, water, and carbon. These ecosystems influence regional and global climate patterns via biogeochemical feedback mechanisms. However, climate change is altering these processes, with rising temperatures intensifying evaporative demand and affecting photosynthetic activity, as indicated by changes in net ecosystem exchange (NEE). Vegetation and biomass variations further impact microclimates, feeding back into heat and water budgets. Understanding the dynamics and meteorological drivers of carbon and water fluxes is essential for comprehending land surface–atmosphere interactions.

This study compares the climatological and ecological functions of tropical wet and dry forests by examining two contrasting sites in the tropical Andes Mountains of southern Ecuador: the montane dry forest (MDF) in the Laipuna Reserve and the montane rain forest (MRF) in the Reserva Biológica San Francisco. The MDF is characterized by a deciduous forest and exhibits pronounced seasonality, with distinct dry (June–December) and wet (January–May) periods, driven by the inter-hemispheric shift of the Intertropical Convergence Zone (ITCZ). In contrast, the MRF experiences year-round rainfall, sustaining an evergreen lower montane forest type. Eddy-covariance measurements were used to monitor water and carbon fluxes under these contrasting climatic regimes. This comparison provides valuable insights into the differential roles of these ecosystems in regulating the Earth's energy and carbon budgets under changing climatic conditions. The objective of the study is (i) to quantify the magnitude and seasonality of NEE and its partitioned components, gross primary production (GPP), and ecosystem respiration (Reco) And (ii) to identify the meteorological drivers responsible for the variations in carbon exchange within each ecosystem. The results reveal significant variations in NEE in the MDF between wet and dry seasons. During the wet season, the average NEE was -3.9 μmol m⁻² day⁻¹, while in the dry season, it declined substantially to -0.8 μmol m⁻² day⁻¹. In contrast, the MRF demonstrated a consistently higher average NEE of -18 μmol m⁻² day⁻¹. These variations are driven by distinct environmental factors. In the MDF, water availability, regulated primarily by precipitation, is the dominant factor influencing carbon exchange. Conversely, the carbon dynamics in MRF are predominantly governed by energy inputs, with light playing a critical role in driving its NEE.