Impact of Human footprint on the climate: FAPAR relationships across Colombia’s ecosystems over the last 21 years

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Yovanny Duran, School of Biology, Universidad Industrial de Santander, Bucaramanga, Colombia, Bjoern Reu, Universidad Industrial de Santander, Colombia and Corina G. Buendia, Universidad Industrial de Santander, Bucaramanga, Colombia

Background/Question/Methods
Photosynthetic activity is a fundamental process that drives the terrestrial biosphere, regulates the carbon cycle, and impacts Earth's climate. Photosynthetic activity, often measured as the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), is modulated by climate factors, such as solar radiation, temperature and precipitation, but also by the physiology of ecosystems and human activity. Because of the feedback mechanisms between photosynthetic activity and climate, it is important to better understand their interactions with human activity; especially in tropical regions with high biodiversity where natural ecosystems still exist. To do so, we analyze the spatiotemporal relationships of monthly precipitation and temperature with FAPAR using correlation analyses. To uncover the impact of human activity on these relationships, we evaluate the relationship of the human footprint index between 1999 and 2019 on the precipitation – FAPAR and temperature – FAPAR relationship.
Results/Conclusions
We find that FAPAR dynamics are in general driven by precipitation and to a lesser extent by temperature. However, the response of FAPAR across Colombia’s ecosystems is diverse. Over large extents of the Carribean and the Andean region, FAPAR responds positively to both temperature and precipitation. Over the Amazon forest FAPAR is positively correlated with temperature, but shows a negative correlation with precipitation. This might be related to the occurrence of clouds during the rainy season that limit solar radiation and hence FAPAR. In the eastern great plains FAPAR is positively correlated with precipitation and negatively with temperature indicating strong droughts where the lack of water and high temperatures limit photosynthetic activity. Interestingly, the Amazonian deforestation hotspots in the department of Caqueta behave similar to the savannas of the eastern great planes. The Chocó biogeographic region, one of the most biodiverse places on Earth, shows all possible combinations of positive and negative correlations and no clear pattern emerges. Evaluating the effect of the human footprint index on FAPAR - climate relationships, we find that it amplifies the precipitation – FAPAR relationship in most Colombian ecosystems, i.e. with increasing human footprint ecosystems respond stronger and faster to precipitation. The effect of the human footprint on temperature - FAPAR relationship is negligible. Our analyses demonstrate how climate and human activity modulates photosynthetic activity under a wide range of climatic conditions in the neotropics. Our findings contribute to a better understanding how climate change and human activity impact ecosystem functioning in the tropics.