Vegetation, fire, climate and human disturbance history in the southwestern Mediterranean area during the late Holocene

Abstract

Detailed pollen, charcoal, isotope and magnetic susceptibility data from an alpine lake sediment core from Sierra Nevada, southern Spain record changes in vegetation, fire history and lake sedimentation since ca. 4100 cal yr BP. The proxies studied record an arid period from ca. 3800 to 3100 cal yr BP characterized by more xerophytic vegetation and lower lake levels. A humid period is recorded between ca. 3100 and 1850 cal yr BP, which occurred in two steps: (1) an increase in evergreen Quercus between 3100 and 2500 cal yr BP, indicating milder conditions than previously and (2) an increase in deciduous Quercus and higher lake levels, between ca. 2500 and 1850 cal yr BP, indicating a further increase in humidity and reduction in seasonal contrast. Humid maxima occurred during the Roman Humid Period, previously identified in other studies in the Mediterranean region. Intensified fire activity at this time could be related to an increase in fuel load and/or in human disturbance. An arid period subsequently occurred between 1850 and 650 cal yr BP, though a decrease in Quercus and an increase in xerophytes. The alternation of persistent North Atlantic Oscillation modes probably played an important role in controlling these humid–arid cycles.

Holocene climate aridification trend and human impact interrupted by millennial- and centennial-scale climate fluctuations from a new sedimentary record from Padul (Sierra Nevada, southern Iberian Peninsula)

“…A suite of proxy previous studies supports our conclusions regarding the aridification trend since the middle Holocene (Carrión, 2002;Carrión et al, 2010;Fletcher and Sánchez-Goñi, 2008;Fletcher et al, 2013;Jiménez-Espejo et al, 2014;Jiménez-Moreno et al, 2015). In the western Mediterranean region the decline in forest development during the middle and late Holocene is related to a decrease in summer insolation (Jiménez- Moreno and Anderson, 2012;Fletcher et al, 2013), which may have decreased winter rainfall as a consequence of a northward shift of the westerlies -a long-term enhanced positive NAO trend -which has induced drier conditions in this area since ∼ 6000 cal yr BP (Magny et al, 2012).…”

“…This trend, however, was superimposed by shorter-term climate variability, as shown by several recent studies from the region (Carrión, 2002;Martín-Puertas et al, 2008;Fletcher et al, 2013;Jiménez-Moreno et al, 2013;Ramos-Román et al, 2016). This relationship between climate variability, culture evolution, and human impact during the late Holocene has also been the subject of recent paleoenvironmental studies (Magny, 2004;Carrión et al, 2007;López-Sáez et al, 2014;Lillios et al, 2016).…”

“…In this study, we used the variations between Mediterranean forest taxa, xerophytes, and algal communities for paleoclimatic variability and the occurrence of nitrophilous and ruderal plant communities and some NPPs for identifying human influence in the study area. Variations in arboreal pollen (AP, including Mediterranean tree species) have previously been used in Sierra Nevada records as a proxy for humidity changes (Jiménez- Moreno and Anderson, 2012;Ramos-Román et al, 2016). The increase or decrease in Mediterranean forest species has been used as a proxy for climate change in other studies in the western Mediterranean region, with greater forest development generally meaning higher humidity (Fletcher and Sánchez-Goñi, 2008;Fletcher et al, 2013).…”

“…Previously, the data were detrended (only in Botryococcus), would produce a progressive cooling, with a reduction in the length of the growing season as well as a decrease in the sea surface temperature (SST; Marchal et al, 2002), generating a decrease in the land-sea contrast that would be reflected in a reduction of the wind system and a reduced precipitation gradient from sea to shore during the fall-winter season. The aridification trend can clearly be seen in the nearby alpine records from the Sierra Nevada, where there was little influence from human activity (Anderson et al, 2011;Jiménez-Moreno and Anderson, 2012;Jiménez-Moreno et al, 2013;Ramos-Román et al, 2016).…”

“…In the western Mediterranean region the decline in forest development during the middle and late Holocene is related to a decrease in summer insolation (Jiménez- Moreno and Anderson, 2012;Fletcher et al, 2013), which may have decreased winter rainfall as a consequence of a northward shift of the westerlies -a long-term enhanced positive NAO trend -which has induced drier conditions in this area since ∼ 6000 cal yr BP (Magny et al, 2012). Furthermore, the decrease in summer insolation (Olsen et al, 2012).…”