Ecosystem Productivity and Evapotranspiration Dynamics of a Seasonally Dry Tropical Forest of the Yucatan Peninsula

Tropical forests are among the most threatened ecosystems despite their important role in the global carbon and water cycles. In Mexico, the Yucatan Peninsula (YP) hosts near to 30% of these ecosystems. We established an ecohydrological monitoring site in a relatively pristine tropical dry forest (TDF) within El Palmar state reserve at the northwest of the YP, to study the seasonal dynamics of its carbon and water fluxes and to evaluate their main controls as they respond to climatic variability. Spatio-temporal analyses using Bio-meteorological data from an Eddy Covariance station (from January 2017 to August 2019) and remotely sensed data (from 2001 to 2019), reveal the inter and intra-annual dynamics of carbon and water fluxes between this ecosystem and the atmosphere. The TDF's greenness, net exchange of carbon, gross primary production, ecosystem respiration, and evapotranspiration are strongly controlled by the seasonality in precipitation pulses and their legacy from recharged moisture in the shallow aquifer observed through three marked seasons: dry, rainy, and post-rainy. The study site continuously behaves like a carbon sink with annual rates ranging between -1.09 and -7.06 tonC/ha/yr ${\mathrm{ton}}_{\mathrm{C}}/\mathrm{ha}/\mathrm{yr}$, whose performance responds to a precipitation threshold above which its productivity declines. Differences in the ecosystem productivity among years result from a combination of water and energy availability during the growing season and variable access to groundwater during the post-rainy and dry seasons. This highlights the ecosystem sensitivity to rainfall modulation of energy and water availability throughout the year and its impact on the ecosystem's functioning and resilience.

Automated summary

Tropical forests, which play an important role in the global carbon and water cycles, are at great risk. The Yucatan Peninsula in Mexico is home to nearly 30% of these forests. A study conducted in a tropical dry forest in this region shows that the dynamics of carbon and water fluxes in the ecosystem are strongly influenced by seasonal precipitation patterns. Furthermore, the productivity of the ecosystem is affected by the availability of water and energy.