Impacts of changing climate and land use on vegetation dynamics in a Mediterranean ecosystem: insights from paleoecology and dynamic modeling

Abstract

Forests near the Mediterranean coast have been shaped by millennia of human disturbance. Consequently, ecological studies relying on modern observations or historical records may have difficulty assessing natural vegetation dynamics under current and future climate. We combined a sedimentary pollen record from Lago di Massacciucoli, Tuscany, Italy with simulations from the LANDCLIM dynamic vegetation model to determine what vegetation preceded intense human disturbance, how past changes in vegetation relate to fire and browsing, and the potential of an extinct vegetation type under present climate. We simulated vegetation dynamics near Lago di Massaciucoli for the last 7,000 years using a local chironomid-inferred temperature reconstruction with combinations of three fire regimes (small infrequent, large infrequent, small frequent) and three browsing intensities (no browsing, light browsing, and moderate browsing), and compared model output to pollen data. Simulations with low disturbance support polleninferred evidence for a mixed forest dominated by Quercus ilex (a Mediterranean species) and Abies alba (a montane species). Whereas pollen data record the collapse of A. alba after 6000 cal yr BP, simulated populations expanded with declining summer temperatures during the late Holocene. Simulations with increased fire and browsing are consistent with evidence for expansion by deciduous species after A. alba collapsed. According to our combined paleoenvironmental and modeling evidence, mixed Q. ilex and A. alba forests remain possible with current climate and limited disturbance, and provide a viable management objective for ecosystems near the Mediterranean coast and in regions that are expected to experience a mediterranean-type climate in the future.

Global change and terrestrial plant community dynamics

“…Forest composition simulated for the last 7,000 y in northern Italy, using temperature as the climate forcing, showed that moderate climate change during the Holocene could not explain the dramatic decline of Abies alba and increase in evergreen oaks detected in the pollen record (119). The observed vegetation changes could only be simulated when increased grazing and frequent fires, associated with Neolithic human settlement, were included in the model.…”

Characterizing Precipitation Variability and Trends in the World’s Mediterranean-Climate Areas

“…For example, declining summer precipitation indicates a trend toward increased seasonality: many places that were moderately or weakly seasonal showed downward trends in summer precipitation, with less precipitation today than in previous decades. This suggests that summers are becoming more harsh, which may cause a shift toward aquatic and terrestrial ecosystems better suited to strongly seasonal conditions [66,67]. Equally significant, downward trends in annual precipitation but not FWS precipitation suggest that precipitation is not declining during the rainy season, but rather during other times of year-possibly during early fall and late spring.…”

1200 years of decadal-scale variability of Mediterranean vegetation and climate at Pantelleria Island, Italy

“…During early Medieval times (ad 700-800), pollen records suggest land-use intensification in the Mediterranean realm (Atherden and Hall, 1999;Colombaroli et al, 2007;Sobrino et al, 2005). Constant grazing and frequent burning eliminated forests and favoured the expansion of garrigue and maquis (Henne et al, 2013;Tinner et al, 2009). Human disturbance in the Mediterranean is often related to burning (Colombaroli et al, 2008;Moreno et al, 1998;Vannière et al, 2011), but the lack of information about palaeo-fire activity on Pantelleria impedes an assessment of the long-term relevance of fire for the island.…”