Federico Di Rita

Holocene drought, deforestation and evergreen vegetation development in the central Mediterranean: a 5500 year record from Lago Alimini Piccolo, Apulia, southeast Italy

Pollen analysis from Lago Alimini Piccolo provides the first record of mid- and late-Holocene vegetation history of a coastal area in the easternmost region of southern Italy (Salento Peninsula). Terrestrial pollen taxa document expansions and declines of the Mediterranean forest, in relation to human activity and climate changes. Between 5200 and 4350 cal. BP a dense evergreen oak forest dominated the landscape; then a distinct opening of the forest is recorded (4350—3900 cal. BP). A new forest expansion (3900—2100 cal. BP) is characterized by an increase of Olea and evergreen shrubs, indicating a development of mediterranean climate conditions and increasing human disturbance. The Roman occupation period (2100—1500 cal. BP) shows a significant opening of the forest, expansion of halophytes and modest values of Olea. After 1500 cal. BP human impact causes a further decrease of the natural woodland in favour of an extraordinary expansion of Olea . The vegetation development at Lago Alimini Piccolo, interpreted in the light of other pollen records, provides new insights into climate evolution and evergreen vegetation development in the central Mediterranean region: (1) a temporary mid-Holocene deforestation at 4000 cal. BP, involving many Italian sites south of 43°N, was possibly caused by drought associated with an expansion or northward displacement of the North African high pressure zone; (2) the Bronze Age increase of Olea, coupled with a widespread increase of Mediterranean shrubs, suggests management of wild trees, while the beginning of intensive cultivation of olive trees is only found after the Roman time.

An overview of the Holocene vegetation history from the central Mediterranean coasts

A review of twenty-six pollen records from coastal areas of central Mediterranean countries (including Malta, Sardinia, Corsica, Italian Peninsula, Sicily, Croatia, and Greece) is presented, in order to describe the general processes characterizing the environmental evolution of this region and to detect the main causes producing landscape change during the last thousands of years. An overview of the main vegetation types shows a rather diverse composition and structure of the vegetational landscape, mostly depending on geomorphic situations, climate conditions, biological processes and human history. This variability makes it impossible to define a pollen stratigraphical scheme valid for the entire area during the last thousands of years. A general and progressive anthropization trend of the vegetational landscape is observed since the Neolithic, evolving with different times and modes from site to site. In many cases human populations adapted their activities to the locally existing natural resources, for example by exploiting native plant taxa (e.g., Olea , Vitis , and Quercus suber ) or transforming natural coastal wetlands in saltworks, always determining deep landscape changes and depletion of the native biodiversity. The responses of vegetation to geomorphic processes and climate have generally been different from site to site: in some cases only one sector of the central Mediterranean Basin was involved (e.g. Tyrrhenian expansion of Alnus around 5200 cal. BP), while in other cases extensive geographical processes occurred (e.g. development of coastal wetlands around 7000 cal. BP). This long-term environmental perspective indicates that the current coastal ecosystems of the central Mediterranean Basin represent an ephemeral snap-shot, destined to new, abrupt and dramatic future changes. Thus, palaeoenvironmental studies may prove of fundamental importance in estimating both the environmental instability typical of each geographical context and the degree of vulnerability of coastal ecosystems, so providing suggestions for appropriate conservation actions in coastal environments.

Holocene forest dynamics in central and western Mediterranean: periodicity, spatio-temporal patterns and climate influence

It is well-known that the Holocene exhibits a millennial-scale climate variability. However, its periodicity, spatio-temporal patterns and underlying processes are not fully deciphered yet. Here we focus on the central and western Mediterranean. We show that recurrent forest declines from the Gulf of Gaeta (central Tyrrhenian Sea) reveal a 1860-yr periodicity, consistent with a ca. 1800-yr climate fluctuation induced by large-scale changes in climate modes, linked to solar activity and/or AMOC intensity. We show that recurrent forest declines and dry events are also recorded in several pollen and palaeohydrological proxy-records in the south-central Mediterranean. We found coeval events also in several palaeohydrological records from the south-western Mediterranean, which however show generally wet climate conditions, indicating a spatio-temporal hydrological pattern opposite to the south-central Mediterranean and suggesting that different expressions of climate modes occurred in the two regions at the same time. We propose that these opposite hydroclimate regimes point to a complex interplay of the prevailing or predominant phases of NAO-like circulation, East Atlantic pattern, and extension and location of the North African anticyclone. At a larger geographical scale, displacements of the ITCZ, modulated by solar activity and/or AMOC intensity, may have also indirectly influenced the observed pattern.

Archaeopalynological Preparation Techniques

The pollen preparation technique consists of a sequence of steps that allow for the removal of organic and inorganic matter from a sample, with the aim of rendering the grains visible under the microscope and enabling easy identification and counting. No special equipment is required, but particular care is needed to avoid contamination of fossil with fresh pollen, and in the use of hazardous chemical products. It is also desirable that all the samples from a stratigraphic sequence be processed using the same procedure in order to avoid different preparation techniques affecting the final results and interpretation of pollen data. Here we describe the standard minimum procedure necessary to extract pollen from archaeological sediments, based on successive treatments with HCl, HF, and NaOH, and a number of modules that can be additionally applied, depending on the composition of the analyzed material. Sieving will be used if the sample composes of a large fraction of sediment coarser than 200 μm or finer than 8 μm. Deflocculation will be applied if the sediment is especially high in clay content. Gravity separation is convenient when samples are poor in pollen and contain very high amounts of mineral fragments. Acetolysis is the last step of the pollen preparation if the samples still contain significant amounts of undissolved organic matter that may affect pollen identification and counting.

The 4.2 ka BP event in the vegetation record of the central Mediterranean

The authors address the effects of the 4.2 ka BP event on forest structure and vegetation composition by using pollen records as proxy for vegetation change. The topic is interesting and timely and suited for discussion in Climate of the Past. The paper concentrates on well-established tools, concepts and ideas and the conclusions reached are interesting. However the scientific methods used and assumptions made are not always valid. In particular pollen-independent evidence of rapid and/or strong climatic change at 4.2 ka BP is not sufficiently developed or considered. This proxy deficiency leads to interpretations and conclusions that are not fully supported by the results. Thus, the paper could be markedly improved by developing and considering independent data and literature, especially on palaeoclimatic evidence, processes and