Abstract
Although human activity is considered to be a major driving force affecting the distribution and dynamics of Mediterranean ecosystems, the full consequences of projected climate variability and relative sea-level changes on fragile coastal ecosystems for the next century are still unknown. It is unclear how these waterfront ecosystems can be sustained, as well as the services they provide, when relative sea-level rise and global warming are expected to exert even greater pressures in the near future (drought, habitat degradation and accelerated shoreline retreat). Haifa Bay, northern Israel, has recorded a landward sea invasion, with a maximum sea penetration 4,000 years ago, during an important period of urban development and climate instability. Here, we examine the cumulative pressure of climate shifts and relative sea-level changes in order to investigate the patterns and mechanisms behind forest replacement by an open-steppe. We provide a first comprehensive and integrative study for the southern Levant that shows that (i) human impact, through urbanization, has been the main driver behind ecological erosion in the past 4,000 years; (ii) climate pressures have reinforced this impact; and (iii) local coastal changes have played a decisive role in eroding ecosystem resilience. These three parameters, which have closely interacted during the last 4,000 years in Haifa Bay, clearly indicate that for an efficient management of the coastal habitats, anthropogenic pressures linked to urban development must be reduced in order to mitigate the predicted effects of Global Change.
Highlights
Mitigating the impact of ongoing climate change and increasing human activities on ecosystems is one of the biggest challenges of the coming decades, at all geographical scales and across all economic spheres [1,2,3,4,5]
We focus on the ratio of actual and potential evapotranspiration (E/PE), which is an index of drought felt by vegetation, and on the difference between annual precipitation and actual evapotranspiration (P-E), which is an estimate of the site’s contribution to run-off in the catchment basin (Fig. 5 and Table S3)
The proxy for vegetation dynamics (PVD) shows that, during the sea incursion deduced from the presence of Dinoflagellate cysts [4000-2900 calibrated year Before the Present], the coastal vegetation evolved from a wet woodland through a shrubland to an open-steppe (Fig. 5) similar to those that can be found nowadays along the coast of Akko, western Galilee (Fig. 3)
Summary
Mitigating the impact of ongoing climate change and increasing human activities on ecosystems is one of the biggest challenges of the coming decades, at all geographical scales and across all economic spheres [1,2,3,4,5]. Coastal ecosystems are among the most threatened because relative sea-level rise associated with global warming renders coastal habitats vulnerable [6,7]. High-resolution climate simulations conducted worldwide predict that temperature increases will severely affect the Eastern Mediterranean (EM) over the century [8,9,10]. An intensification of extreme weather events is predicted to interact with patterns of species distribution even if non-climatic influences may dominate local short-term biological shifts [11]. Regional patterns of warming-induced changes in hydrology seem to be more complex and less certain than those in temperature, in the EM’s seabord areas [8,12,13]. Shoreline changes, which may result from a range of interacting physical and chemical processes, will have important consequences for biological features of the EM coastlines [14,15]
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