Elevational variation in regional vegetation responses to late-glacial climate changes in the Carpathians

Aim: We used fossil records to explore patterns of change in vegetation composition, turnover and diversity along an elevational gradient during the late-glacial to early Holocene, and to locate the elevations most sensitive to past climate changes. Location: Romania. Methods: Changes in the late-glacial vegetation communities were inferred from seven published pollen records distributed within the main vegetation belts of the Romanian Carpathians, at elevations from 275 to 1840 m. Principal components analysis, detrended canonical correspondence analysis (DCCA) and rarefaction analysis were undertaken on these data. Results: DCCA indicates that compositional change is strongest (SD 1.2, c. 70%) at the late-glacial/Holocene transition (c, 11,500 cal. yr BP), but significant shifts also occur at c. 14,700, c. 13,800 and c. 12,700 cal. yr BP (SD 0.4-0.8, 25-50%). Palynological turnover is greater for mid-elevation records (730-1100 m) than at low and high elevations. Intervals of greater palynological richness occur between c. 13,800 and 12,500 cal. yr BP and after 11,500 cal. yr BP, and intervals of lower richness occur before c. 14,000 cal. yr BP and between c. 12,900 and 11,500 cal. yr BP. Main conclusions: Variations in species composition during repeated climate changes of the late-glacial suggest that community composition at a given time was not only a result of the environmental conditions of that period, but also the legacy of previous cumulative recruitment and extirpation events. Turnover estimates suggest that mid-elevations have been the most sensitive to climate change during the late-glacial and early Holocene. Palynological richness estimates show a less clear elevational pattern and no evidence for a greater sensitivity of this measure of biodiversity at high elevations to past climate change. However, results may have been affected by taxa with high pollen productivity and distance dispersability. Our finding concurs with other palaeoecological and local-scale modelling studies in suggesting that small populations have survived in favourable microhabitats embedded within larger unsuitable areas during the late-glacial, features not captured by broad-scale model predictions.