Paleoecología de dos puntos calientes de la biodiversidadlos parques nacionales de Doñana y Sierra Nevada

Resumo

Palaeoecological data-series provide information at long temporal scales allowing the identification of ecological patterns and processes useful to inform the setup of strategies for the management and conservation of nature. The application of a longer-term approach for the understanding of patterns and processes of ecological change is especially relevant in those settings where biodiversity concentrates. Two southern Iberian biodiversity hotspots stand out within the Mediterranean basin: the Doñana National Park, located in a coastal environment, and the Sierra Nevada National Park, located in a mountain environment. This doctoral dissertation presents two new palaeoecological records for the Doñana National Park and one new palaeoecological record for the Sierra Nevada National Park aiming i) to increase the taxonomic and chronological resolution of the available palaeoecological information of the southern Iberian Peninsula, ii) to reconstruct the dynamics of different vegetation formations to a variety of environmental disturbances; iii) to identify the ecological traits contributing to the existence and maintenance of high biodiversity levels at both National Parks, and iv) to assess the usefulness of palaeoecological data for biological conservation purposes. The palaeoecological records obtained at the Doñana National Park reconstruct the vegetation history of the marshlands at the mouth of the Guadalquivir river (Lucio de la Cancela de la Aulaga, LuCA) from 9900 to 6500 cal. yr BP, and of a seasonal wetland (Laguna de El Sopetón, ElSo) along three discontinuous periods during the Holocene. The origin of the LuCA environmental archive is linked to the sedimentary infilling and enclosure of the estuary of the Guadalquivir river. In addition, two tsunamis punctuate the LuCA sedimentary record during the Early Holocene. The LuCA palaeoecological record features stable upland and marshland landscapes during the Early Holocene, despite the occurrence of the two high-energy events. This stability contrasts with the reconstruction of a very dynamic Middle Holocene when changes in the upland systems reflect in the aquatic communities. On the other hand, the ElSo environmental archive shows three organic packages separated by sandy layers that provide evidence for the development of a hydromorphic soil from 6900 to 6500 cal. yr BP, and two wetland phases in historical times (AD 40-350 and AD 1550-present). The ElSo palaeoecological record links the configuration and mobility of the sandy substrate with the upland and wetland diversity dynamics. The dune system dynamism evidences the existence of a dynamic baseline condition, so conservation measures on Doñana's ecosystems should not consider fixed baselines. Both Doñana palaeoecological records demonstrate the importance of the groundwater dynamics as connecting elements between the upland and aquatic systems. The palaeoecological record obtained at the Sierra Nevada National Park (Laguna de la Mosca, LdlMo) reconstructs the vegetation dynamics in a mountainous environment for the last 8400 years. The reconstruction shows how the Early Holocene pine forests transitioned towards mixed Pinus-Quercus submediterranean forests as a response to a decrease in seasonality 7300 years ago. Subsequently, the pine-oak submediterranean forests drastically collapsed towards an open landscape dominated by evergreen Quercus formations after an aridity crisis 4200 years ago. The ecological differences in the structure and functioning of the mixed submediterranean forests compared to the pinelands meant a threshold response to the fire events 4200 years ago, provoking the establishment of a Mediterranean sclerophyllous vegetation. This record also contributes to the recognition of groundwater discharges as a buffering mechanism against climatic aridity, influencing the response of the vegetation at different altitudinal belts. Overall, the three palaeoecological records obtained at two biodiversity hotspots and presented in this doctoral dissertation portray the importance of the continuous provision of liquid water in the maintenance of the high biodiversity levels at both the Sierra Nevada and the Doñana National Parks. Likewise, the findings show the importance that the palaeoecological approach has for obtaining ecological scenarios that could be used as analogous to understanding the impact that forecasted global change could have on Iberian forests. Finally, the value of incorporating a palaeoecological approach as an empirically-based theoretical framework for the planning and design of biodiversity conservation measures is emphasised.