Holocene history of Aleppo pine (Pinus halepensis Mill.) woodlands in the Ebro Basin (NE Spain). Climate-biased or human-induced?

This paper reviews the past distribution of Aleppo pine woodlands in the Ebro Basin, Northeastern Iberia, from the Mesolithic to Modern times based on wood charcoal data. The aim is to detail the chronological timing and the drivers explaining the long-term presence of Aleppo pine woodlands and associated thermophilous flora. The available charcoal data support the early spread of Pinus halepensis during the Mesolithic (ca. 9000 cal BP) accompanied by Mediterranean trees and shrubs like Quercus sp. evergreen, Juniperus sp., Arbutus unedo, Pistacia lentiscus, Rhamnus/Phillyrea, Cistaceae, and Rosmarinus officinalis, as a local response to global climate change in the Early Holocene. During the arrival and the propagation of the Neolithic culture (ca. 7500–5500 cal BP), anthracological records, as well as regional palynological sequences, demonstrate the progressive replacement of an conifer-dominated open parkland by both Quercus sp. deciduous and evergreen woodlands in response to the Middle Holocene rise in temperature and humidity. This evidence, however, converges with the general idea that the presence and the spread of Pinus halepensis and associated scrubland have usually been attributed to the onset of landscape anthropization. The frequency of xero-thermophilous open scrubland and the use of Aleppo pine for fuel and woodcrafting progressively increased during the Bronze and Iron Ages, and especially in Ibero-Roman and Medieval/Islamic times, when the vegetation landscape in the Middle Ebro Basin was largely deforested as a consequence of increasing demographic pressure, grazing and the establishment of proto-urban centers.