Pan-Mediterranean Holocene vegetation and land-cover dynamics from synthesized pollen data

Aim: The Mediterranean is characterized by diverse and spatially heterogeneous mosaic landscapes. Within this study, a cluster analysis-based method is developed for the classification of Mediterranean vegetation types based on modern and fossil pollen datasets. The application of this approach to multiple pollen records spanning the Mediterranean region has allowed temporal variations in vegetation dynamics to be explored throughout the Holocene. We ask how far back stable baseline vegetation communities can be identified in the pollen record, and whether those types considered to be characteristic of the Mediterranean landscapes have been present in the past as well as at the present. Location: The research location includes the land areas surrounding the Mediterranean Sea. The pollen sites are principally located in mainland Spain, southern France, Greece and Turkey, Italy, North Africa, the Levant, and some Mediterranean islands. Methods: A total of 5,641 samples from 158 fossil pollen records (cores) and 1,799 modern pollen surface samples were harmonized taxonomically and pollen count data summed into 200-year time windows on a common time-scale from 11,000 BP to the present-day. Cluster analysis and community classification were used to identify major vegetation types along with other approaches to explore patterns in ecological datasets, such as Simpson's diversity index and nonmetric multidimensional scaling. Results: The pollen datasets were classified into 11 closed forest/woodland and five open or scrubland vegetation types. Closed vegetation clusters declined from the mid-Holocene with a marked increase in open or human-modified vegetation types since 3,500 BP and with an increasing rate of vegetation change and habitat diversity through time. Main conclusions: The Mediterranean has been a dynamic landscape throughout the Holocene with frequent changes in land cover identified in the pollen datasets. The pollen-inferred clusters reveal a wider range of Mediterranean vegetation types than identified in previous studies; for example, including both beech and alder woods. Evergreen Oleaceae-dominated shrubland is much better represented in modern than in fossil samples while mesic forest was abundant in the past but is uncommon today.