Forests near the Mediterranean coast have been shaped for millennia by intense human disturbance. Consequently, it is difficult to distinguish the effects of past climatic change on vegetational dynamics from human impacts, or even determine what the natural vegetation in the absence of intense human disturbance might be. We used a combined dynamic vegetation modeling/paleoecological approach to explore the relationships among climate, vegetation, and human impacts at two sites in Italy. Dynamic modeling allows us to isolate the impacts of climate and human disturbance, while paleovegetational reconstructions provide a means to validate simulation output with empirical data. Our study landscapes surround lakes with well-dated, high-resolution paleovegetational reconstructions and are situated in climatically distinct regions. Lago di Massaciuccoli in coastal Tuscany is located near the northern extreme of the evergreen broadleaved vegetation belt, and Gorgo Basso is situated in southwestern Sicily. Both sites experience mild moist winters and hot dry summers, although Gorgo Basso is warmer and drier in all months. We simulated vegetation with the LandClim dynamic landscape model with a 5000 year simulation period.
Results/Conclusions
Vegetation simulated with modern climatic inputs is consistent with pollen-inferred vegetational reconstructions. For instance at Lago di Massaciuccoli, a forest dominated by evergreen oak (especially Quercus ilex), with abundant fir (Abies alba), and a small component of broadleaved deciduous trees was simulated. This unusual community has no extant analogue, but is remarkably consistent with pollen data predating extensive human disturbance (i.e., before 6000 cal yr BP). On dry soils near Gorgo Basso, LandClim simulated an open forest with olive (Olea europea) as the most abundant species. Closed forests of evergreen oak and olive are simulated on more mesic soils. Again, no similar community exists on the modern landscape, but simulation data corroborate palynological evidence for olive-evergreen oak woodlands in Sicily before about 2700 cal yr BP. Our results show that increasing human disturbance largely eliminated fire sensitive species (e.g., fir) and vegetation types (e.g., closed evergreen oak forests, native olive woodlands) from coastal Mediterranean ecosystems. Agreement between modeled and reconstructed vegetation implies that the current, highly-flammable vegetation typical of coastal Mediterranean ecosystems is perpetuated by human disturbance, not climatic conditions. In the absence of frequent disturbance extinct vegetation types that rarely burn could persist in the Mediterranean region.
