Tropical forest soils store a third of the global terrestrial carbon and control carbon dioxide (CO2) terrestrial effluxes to the atmosphere produced by root and microbial respiration. Soil CO2 efflux varies in time and space and is known to be strongly influenced by soil temperature and water content. However, little is known about the influence of seasonality on soil CO2 efflux, especially in tropical dry forests. This study evaluated soil CO2 efflux, soil temperature, and soil volumetric water content in a semideciduous tropical forest of the Yucatan Peninsula under two sites (flat areas close to and far from hills), and three seasons: dry, wet, and early dry (a transition between the rainy and dry seasons) throughout a year. Additionally, six 24-h periods of soil CO2 efflux were measured within these three seasons. The mean annual soil CO2 efflux was 4±2.2 μmol CO2 m-2 s-1, like the mean soil CO2 efflux during the early dry season. In all seasons, soil CO2 efflux increased linearly with soil moisture, which explained 45% of the spatial-temporal variation of soil CO2 efflux. Soil CO2 efflux was higher close to than far from hills in some months. The daily variation of soil CO2 efflux was less important than its spatial and seasonal variation likely due to small diel variations in temperature. Transition seasons are common in many tropical dry forests, and they should be taken into consideration to have a better understanding of the annual soil CO2 efflux, especially under future climate-change scenarios.
<p><strong>Background</strong>: The Yucatan Peninsula is covered mainly by semi-humid forests associated with karstic zones. These landscapes show high rates of endemism, and although they are resilient ecosystems, climatic variations place them as highly susceptible areas to climate change. <strong>Objective:</strong> To identify environmental and anthropogenic risk factors in the semi-humid forests of the Yucatan Peninsula, and to evaluate the vulnerability to climate change of 25 forest species with economic importance in this region. <strong>Methodology:</strong> A multi-criteria analysis was carried out to rank edaphic and climatic variables, changes in potential distribution due to climate change, species density and growing rate. These variables were integrated into a matrix and each variable was valued from 0 to 4, weighted between parameters, the higher the value, the greater the susceptibility. Four percent of the species were classified into the high-risk susceptibility and 84 % as medium risk and the rest as low. These species have a low density per hectare, have a restricted distribution, are slow growing and are over shallow soils. <strong>Implications: </strong>Species that can develop in a wide range of environmental conditions and have rapid growth rates were less susceptible to the risk factors analyzed here. <strong>Conclusions:</strong> The greatest risk factor was due to the effect of climate change, followed by the proximity to the Caribbean coast and the type of soil, which suggests that more conservation actions for forest species are needed, which will also ensure the provision of environmental services to human populations.</p>
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