engleski

Reconstructing Holocene Vegetation in Area of Baćina Lakes

We provide first palynological analysis of sediments from the Baćina lake Crniševo. The palynological record span thru the Holocene (c. 11300-0 cal. yr BP). In the analysed samples from the core Baj-7, we can observe the transition of vegetation in the wider studied area from a mixed forest in a moderately warm humid climate at the end of the Pleistocene to Mediterranean vegetation in the Mediterranean climate.Changes in palynomorphs (spores, pollen, phytoplank-ton, and zooplankton) match with changes in geochemical parameters such as N, TOC and C/N. This congruence allowed a better interpretation of some changes as well as increase or decrease of (palynomorph) values.There are nine zones and nine subzones that correlate to the changes in climate, vegetation, and trophicity. Samples of the oldest PZBAJ-I zone were deposited in the shallow hypertrophic lake at the time of the rapid rise in sea level (MWP-1B) before 11.3 cal. yr BP. Hypertrophic condi-tions also existed at the time of the PZBAJ-II zone which coincides with the onset of deposition of the sapropel S1a 10800-8800 cal BP at the beginning of the Holocene. Zone PZBAJ-III occurs in the proximal, i.e., the shallower part of the mesotrophic lake. During the zone PZBAJ-IV, the lake changes from the mesotrophic to the oligotrophic condi-tion. Warming and the decrease of precipitation occur, and the freshwater green alga Botryococcus braunii appears. For the PZBAJ-V zone, remarkable is a low percentage of green algae Coelastrum polychordum. A gradual decrease in the share of cyanobacteria Gloeotrichia, as well as a noticeable share of elements of Mediterranean vegetation (Quercus ilex -type and Ostrya type) and heathers (Ericaceae), is shown. The PZBAJ- VI area is divided into six subzones where the humid and drought periods change, i.e., the second-ary succession of vegetation due to the deforestation. The first subzone is PZBAJ-VIa, in which the share of Medi-terranean vegetation elements generally reduces, while the proportion of deciduous vegetation increases, suggesting a more humid climate with more rainfall. But, at the begin-ning of the zone, there is a decrease in the proportion of deciduousoak and the increased proportion of the heathers (Ericaceae) and grass (Poaceae) which may correspond to the drought period 4200 BP. The subzone PZBAJ-VIb is dominated by amorphous liptinite of algal origin which indicates an increased primary organic production. The subzone PZBAJ-VIc shows a sudden increase in the pro-portion of nitrogen due to the high share of green algae Coelastrum polychordum and occurrence of alder (Alnus). There is a decreased proportion of heathers (Ericaceae) and grass (Poaceae), and an increased proportion of ferns. That indicates secondary succession that can be traced from this subzone. After the oak forests clearings (some 3500 years ago), ferns and alder appear as pioneer species followed by the fir increase, and pine increase at the end of the subzone. The oak increase occurs in the next subzone PZBAJ-VId as the vegetation is renewed. At the end of the subzone (some 3200 years ago), evidence of clearings is again evident fol-lowed by subsequent forest recovery during the subzone PZBAJ-VIe. The most intensive forest clearings (some 2200 years ago) occur during the PZBAJ-VIf subzone. And again forest is being renewed during the PZBAJ- VIIb subzone (some 1800 years ago, i.e., 200 AD). The share of pollen of trees decreases in the subzone PZBAJ-VIIc, while the proportion of algae, heathers, and grass increa- ses, corresponding to the medieval warm period when the lake changes from mesotrophic to the eutrophic conditions, which remains to the present.This work was supported by the Croatian Science Foun-dation Project, “Lost Lake Landscapes of the Eastern Adri-atic Shelf ” (HRZZ-9419).

Holocene, palynology, climate, Croatian Adriatic coast

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