Variation of the forest and herbaceous domains in the landscape of the Iberian Peninsula in the last 20,000 years. Importance of the effect of large herbivores on vegetation

Mega-herbivores (body mass greater than 1000 kg) help structuring the plant landscape through consumption, breakage and uprooting of numerous woody plants, tending to transform wooded areas into grass, shrub and forest mosaics. These mosaics contribute to maintain a high biodiversity, since they enable the persistence of plants and animals of dense forests and treeless steppes, which alternated in the European landscapes following the glacial cycles of the Pleistocene. The disappearance of the mega-herbivores from the Iberian Peninsula at the end of the Pleistocene probably caused a cascade of ecological effects that remains unknown. We also do not know if the causes of their disappearance were natural or anthropogenic, and consequently it is not know if the plant landscapes that developed later, in the Holocene, have a natural or anthropogenic origin. The aim of this review is to explore in the scientific literature the hypothesis that the transformation of the natural landscape by humans began after their arrival in Europe through the intensive hunting of large herbivores, until their disappearance or extreme reduction. Consequently, the forest recovery of the end of the Pleistocene and beginning of the Holocene might have taken place without the containment that these animals would have exerted on woody vegetation in the previous interglacials. As a result, dense forests would spread over large territories reducing pastures and herbivores of open spaces, which were the sustenance of Homo sapiens in the Pleistocene. This limitation would force humans to change their diet to survive and, in a relatively short period of time, to adopt a new way of life-style based on livestock and agriculture. The results of the review do not allow us to support or reject the hypothesis raised, or even any of the most relevant issues arising from it. Some fundamental grounds of this hypothesis are currently debated, and are giving rise to contrasting interpretations. The most relevant ecological aspects found after the literature review are discussed, some ideas are proposed for their interpretation, and the limitations of the paleo-ecological information available in the literature to answer general questions such as those posed here, are emphasized.

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