The human impact imprint on modern pollen spectra of the Maya lands

To understand human occupation in the context of paleoecological records from the Maya region, there is need to explore the distribution of modern pollen along climate and human-impact gradients. In this study, we analyze the responses of pollen assemblages from 125 surface samples to human influence in the Maya region, using three basic approaches: (i) the evaluation of using modern pollen spectra to distinguish the main anthropogenic and natural vegetation types; (ii) the usage of detrended correspondence analysis (DCA) to evaluate the distribution patterns of pollen along environmental gradients including human influence; and (iii) the evaluation of the responses of taxon-specific elements to the human-influence gradient, that expresses on the modern landscape, using threshold-indicator taxa analysis. The 125 locations where mud-water interface samples were retrieved were divided into four groups that correspond to the major vegetation types of the Maya region (coniferous and Quercus forest, croplands and pastures, tropical seasonal forest, and tropical evergreen forest). In terms of individual taxa responses, we detected 20 elements significantly related to the human-influence gradient. These were assigned to negative (decreasing) or positive (increasing) response groups depending on the response direction. Mostly arboreal elements from tropical seasonal forests decreased, while non-arboreal elements typically from anthropogenic vegetation increased in response to different levels of human influence. Also, a community-level abrupt point change is detected at a human influence index of 15. When human influence exceeds this threshold, important elements of the natural vegetation are negatively affected while opportunistic elements become favored. Overall, the study of pollen distribution along environmental gradients and the identification of taxa indicators of human impact provide valuable tools for the interpretation of fossil pollen records from the Maya region.