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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/218652
Spatiotemporal Changes in Mountain Plant Communities of the Central-Eastern Region of the Trans-Mexican Volcanic Belt Over the Last 17,000 Years
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[eng] Neotropical mountains are known for their high biodiversity and endemism, providing numerous ecosystem services to the surrounding areas. However, mountain biodiversity is rapidly declining due to climate change and anthropogenic activities.
The present thesis uses pollen analysis to investigate changes in high mountain neotropical plant communities in the central-eastern region of the Trans- Mexican Volcanic Belt (TMVB), in Central Mexico, over the past 17 kyr. Two study sites have been integrated into this thesis: Cofre de Perote and Iztaccíhuatl volcanos. At an elevation of 3700 m asl, the pollen assemblage of a sedimentary record from Cofre de Perote volcano was analysed, supported by charcoal, Magnetic Susceptibility (MS), and Ti concentration analyses. This research documented the vegetation reorganisation and plant colonisation of high elevations after the glacial retreated due to temperature increase during the Early and Mid-Holocene. The results suggested that during the Early Holocene, forests were maybe closer and/or at higher elevations in Cofre de Perote, near the coast, than at similar elevations in inland sites. The results also revealed that the influence of winds on long-distance pollen arrival could play a crucial role in understanding the pollen assemblages in highland sites. Additionally, Picea pollen presence indicated the occurrence of non-analogue communities in this site and its potential role as microrefugia during the Early Holocene.
In the Iztaccíhuatl volcano, the pollen deposition in surface soil samples from the current plant communities along an elevation gradient was analysed. The results suggested that high percentages of Abies were related to the presence of a Fir Forest. High Pinus values and Arceuthobium pollen presence could be associated with Pine Forest. Pollen taxa such as Apiaceae, Eryngium, Valerianaceae, and Caryophyllaceae are linked to Pine Forest and Alpine Grassland. Secondly, the research focused on studying past plant communities' distribution along the volcano's elevation gradient via pollen analysis of palaeosol samples from three elevation transects. The samples collected in each elevation transect spanned a specific age (time window) during the Late Quaternary. The recovery of samples was made using three tephras that potentially sealed the soil protecting the palynomorphs from degradation, and at the same time, worked as chronostratigraphic markers for this research:
Tutti Frutti (~17 cal kyr BP), Ochre (~5.7 cal kyr BP), and Pink (~1.1 cal kyr BP/840 CE) Pumices. In addition, the eruption events resulting in the tephra deposits occurred coeval to three distinct climatic events: Heinrich Event-1 (HE-1), Holocene Thermal Maximum (HTM), and Medieval Climatic Anomaly (MCA). Results indicated that samples at ~17 cal kyr BP lack sufficient pollen grains to propose an accurate paleoenvironmental interpretation. At
~5.7 cal kyr BP, high Poaceae pollen values suggested the extensive presence of open vegetation. At ~1.1 cal kyr BP, the presence of Mixed Forest between ~3300 and 3450 m asl, Pine Forest between 3450 and 3700 m asl, and a more extended ecotone zone between Pine Forest and Alpine Grassland was proposed. Inferred plant community distribution and structure changes at ~5.7 and ~1.1 cal yr BP may be linked to warm and dry conditions during HTM and MCA, which seemed to have a larger effect on trees than on herbs.
The join interpretation of this thesis has revealed the vulnerability of coniferous forests to global warming and human activities. These past and current threats could be involved in:
(i) a possible recent expansion of Fir Forest around the Iztaccíhuatl volcano and other areas of the TMVB; and (ii) the evidence of Picea local extinction in TMVB during the Early Holocene, suggesting that species with restricted distributions or isolated populations are at risk. Finally, the importance of natural reserves and conservation programs is highlighted.
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RODRÍGUEZ PÉREZ, Erandi tzayani. Spatiotemporal Changes in Mountain Plant Communities of the Central-Eastern Region of the Trans-Mexican Volcanic Belt Over the Last 17,000 Years. [consulta: 26 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/218652]