Vegetation History in the Toledo Mountains (Central Iberia): Human Impact during the Last 1300 Years

Late Holocene vegetation responses to climate change and human impact on the central Tibetan Plateau

Understanding long-term environmental changes under natural and anthropic forces is helpful for facilitating sustainable development. Here we present a sedimentary record from the central Tibetan Plateau to investigate the impacts of climate and human activities on alpine vegetation during the late Holocene, based on a 162-cm-long lacustrine sediment core collected from Tangra Yumco. Palynology, charcoal and minerogenic input reveal variations of climate and human activity during the past 3400 cal yr BP. Our results show that alpine steppe dominated by Artemisia, Cyperaceae and Poaceae was present in the Tangra Yumco area during the entire covered period. Only minor human activities are visible between 3400 and 2300 as well as from 1700 to 400 cal yr BP, when vegetation was mainly influenced by climate. Although human activities (presence/grazing) became more intensive between 2300 and 1700 cal yr BP corresponding to the Zhang Zhung Kingdom, vegetation change is still mainly affected by a more arid climate. Strongest human influence on vegetation was found after 400 cal yr BP, when vegetation composition was altered by farming and grazing activities. Our records indicate human activities did not have significant impacts on alpine environment until the past few centuries at Tangra Yumco on the central Tibetan Plateau.

The Toledo Mountains: A Resilient Landscape and a Landscape for Resilience? Hazards and Strategies in a Mid-Elevation Mountain Region in Central Spain

The Toledo Mountains are a mid-elevation mountain range that separates the Tagus and Guadiana basins in the central area of the Iberian Peninsula. The location of these mountains allows the development of typical Mediterranean vegetation with some Atlantic influence. Consequently, typical broadleaved evergreen Mediterranean vegetation currently dominates the regional landscape, with the remarkable presence of more mesophilous species in sheltered and more humid microsites such as gorges (e.g., Prunus lusitanica, Taxus baccata, Ilex aquifolium) and mires/bogs (e.g., Betula pendula susbp. fontqueri, Erica tetralix, Myrica gale). Palaeoecological studies in these mountains are essential to understand the long-term ecology and original distribution of these valuable communities and are key to assess their resilience. Understanding the hazards and opportunities faced in the past by the plant communities of the Toledo Mountains is necessary to enhance the management and protection of those species currently threatened. This study focuses on El Perro mire, a peatland on the southern Toledo Mountains (central Spain) where climatic variability has played a major role in landscape dynamics at multi-decadal to millennial timescales. Climatic events such as the 4.2 ka cal. Before Present (BP) or the Little Ice Age triggered relevant landscape changes such as the spread and latter decline of birch and hazel forests. Human communities also seemed to be affected by these events, as their resilience was apparently jeopardized by the new climatic conditions and they were forced to find new strategies to cope with the new scenarios.

Unprecedented herbivory threatens rear-edge populations of Betula in southwestern Eurasia

Mediterranean rear-edge populations of Betula, located at the southwestern Eurasian margin of the distribution range, represent unique reservoirs of genetic diversity. However, increasing densities of wild ungulates, enhanced dryness, and wildfires threaten their future persistence. A historical perspective on the past responses of these relict populations to changing herbivory, fire occurrence and climatic conditions may contribute to assessing their future responses under comparable scenarios. We have reconstructed vegetation and disturbance (grazing, fire) history in the Cabañeros National Park (central-southern Spain) using the paleoecological records of two small mires. We particularly focused on the historical range of variation in disturbance regimes, and the dynamics of rear-edge Betula populations and herbivore densities. Changes in water availability, probably related to the North Atlantic Oscillation (NAO) index, and land-use history have played a crucial role in vegetation shifts. Our data suggest that heathlands (mainly Erica arborea and E. scoparia) and Quercus woodlands dominated during dry phases while Sphagnum bogs and Betula stands expanded during wet periods. Betula populations survived past moderately dry periods but were unable to cope with enhanced land use, particularly increasing livestock raising since ~1,100-900 cal. yr BP (850-1,050 CE), and eventually underwent local extinction. High herbivore densities not only contributed to the Betula demise but also caused the retreat of Sphagnum bogs. Ungulate densities further rose at ~200-100 cal. yr BP (1750-1850 CE) associated with the historically documented intensification of land use around the Ecclesiastical Confiscation. However, herbivory reached truly unprecedented values only during the last decades, following rural depopulation and subsequent promotion of big game hunting. For the first time in temperate and Mediterranean Europe, we have used the abundances of fossil dung fungal spores to assess quantitatively that current high herbivore densities exceed the historical range of variation. In contrast, present fire activity lies within the range of variation of the last millennia, with fires (mainly human-set) mostly occurring during dry periods. Our paleodata highlight the need of controlling the densities of wild ungulates to preserve ecosystem composition and functioning. We also urge to restore Betula populations in suitable habitats where they mostly disappeared because of excessive human activities.