Understanding ecosystem dynamics of herbaceous grasslands (Campos) and arboreal forests (Bambuseae) using Poaceae pollen grains in the Coastal Plains Holocene sediments of Southern Brazil

In this study we analysed fossil Poaceae pollen of the Holocene from the Coastal Plain of Rio Grande do Sul (aguas Claras region), southern Brazil. Through light microscopy analysis, we measured the size of 60 pollen grains in the 28 samples (or, in samples with low frequency of Poaceae, sufficient pollen grains for the number of measurements to show a stability curve). The measurements of fossil Poaceae pollen were interpreted applying information from the modern Poaceae pollen dataset. Fossil Poaceae pollen showed changes from the Early Holocene to the present. Results showed that it is possible to obtain more ecological information (vegetation and climate changes) from fossil Poaceae pollen. Furthermore, dynamics of Poaceae vegetation during the Holocene are revealed. The palynological record documents the predominance of Poaceae herbaceous grasslands (63%) during the Early Holocene (10,974 +/- 49 C-14 BP) and the low representation of Poaceae arboreal forests (Bambuseae - 15%). Vegetation changes are detected from 3420 years BP with an increase in Poaceae arboreal forests (75%) and a decrease in Poaceae herbaceous grasslands (115 cm). This significant change may indicate the late vegetation shift in response to sea-level change. At 1072 years BP, a peak of Poaceae arboreal forests (85%) indicates warm conditions. The representation of Poaceae arboreal forests (Bambuseae) decreased drastically (27%) at 536 years BP. Pollen grains from samples closer to the surface (5 and 15 cm) reflect modern vegetation in the region. Poaceae pollen is shown to be sensitive to climate changes and therefore useful for the analysis of dynamics of grassland and forest vegetation.