Characteristics of Poaceae pollen grains as a tool to assess palaeoecological grassland dynamics in South America

Lisa Schu ler 0 Hermann Behling 0 0 L. Schuler (&) H. Behling Department of Palynology and Climate Dynamics, Albrecht- von-Haller Institute for Plant Sciences, Georg-August-University of Gottingen , Untere Karspule 2, 37073 Gottingen, Germany During the Quaternary, in particular during glacial times, different grassland ecosystems played a much larger role and had a significantly larger distribution. Little is known yet about past development, biodiversity and dynamics of grassland ecosystems. In this innovative study, we attempt to distinguish between different South American grassland types in space and time based on morphological pollen grain characteristics of Poaceae. For this purpose [60-80 Poaceae pollen grains of 20 grassland samples were measured using their length, width and pore diameter as well as annulus width. Samples were taken from five sites in wet Paramo vegetation from the Late Pleistocene to the Late Holocene in South Ecuador and from two sites in the south-eastern Brazilian highlands (Campos do Altitude) of the same period. Additionally, we investigated two samples from a Pampa site as well as six samples from one Campos grassland site in southern Brazil from the Late Pleistocene to the Late Holocene. Subsets of samples of the Campos grasslands and of the Paramo were investigated in order to retrieve more detailed information on patterns within these vegetation types. Multivariate data analysis of the complete data set shows changes in taxonomic composition along an elevational gradient in the Paramo grasslands. Our results reveal a highly dynamic development of the individual grassland types; they also provide interesting information on Poaceae taxa composition patterns, development and possibly changes in biodiversity within these ecosystems. Moreover, our data provide an indication about the origin and dynamics of the Campos ecosystems in the southern Brazilian highlands during the Late Pleistocene and the Holocene before and after the onset of human activities. - Despite the dominance of grassland ecosystems in South America during the Pleistocene and also despite their high biodiversity, which makes them important for conservation (Behling and Pillar 2008; Overbeck et al. 2005, 2007), these biomes have received little attention so far. In South America different grassland ecosystems covered much larger in areas during the past, in particular during the Pleistocene (Behling and Hooghiemstra 2001). Spatial variations of grassland ecosystems in subtropical and tropical climates as well as changes in composition of grassland vegetation, and locations and shifts of boundaries play an important role in past climate reconstruction (Behling 2002). Furthermore, in order to understand the different grassland areas today, we need to investigate their origin, development and dynamics. Unfortunately, due to the rather uniform morphology of Poaceae pollen grains (Andersen 1979; Beug 1961, 2004) and the very high numbers of species in many regions (Overbeck et al. 2007; Sklenar and Balslev 2005), it has been very difficult, if not even impossible so far, to relate past grassland types to known grassland communities. Since the pollen grain morphology of Poaceae is mostly uniform, it does not allow the determination of pollen grains down to subfamily level in most cases. Pivotal details only become visible using a 6001,0009 magnification and oil immersion light microscopy. This however is, when aiming at determining a representative amount of grains for many samples, very intricate and time-consuming. We collected data on measurable parameters of pollen grains to develop a rather quick and effective method to distinguish between grassland communities. Earlier results reveal that cereal pollen grains can be distinguished from wild grass pollen grains when using a combination of the criterion of grain diameter and the criterion of pore diameter (Andersen 1979; Beug 1961, 1992, 1994; Joly et al. 2007). However, these authors assumed that a characterization of grassland types by the use of Poaceae pollen grains was not possible due to the fairly large number of grains they studied which revealed a normal distribution of grain size. This was predicted to be the outcome of all investigations of grassland types based on pollen grain measurements on Poaceae (Salgado-Labouriau and Rinaldi 1990a, b). Nevertheless, it is often observed that specific Poaceae pollen grain types are only found in certain grassland samples. The conspicuously different grain sizes of this plant family add to the impression that there must be apparent differences between grassland ecosystems. In a first study on the development and the application of this approach we showed that it is possible to distinguish between South American grassland types using Poaceae pollen grain size (Schuler and Behling 2010). With our approach we seek to derive more detailed information on palaeograssland dynamics. In this study we aim to show how more detailed information on grassland dynamics can be derived with our approach. We measured four parameters of Poaceae pollen grains in samples from four different grassland types throughout South America. For a first classification of grasslands and a sufficiently clear separation between them, the mean grain length of a grassland pollen grain type yielded enough information. However, further approaches have shown that the analysis of grain length combined with multivariate data analysis in which all grain size parameters are considered, offers a great potential for more detailed information (Schuler and Behling 2010). The aim was to use these quantifiable morphological characteristics of Poaceae pollen grains in order to investigate resemblances, differences and changes in taxa composition within and among the different grassland types on a spatial and a temporal scale as well as biodiversity patterns. We also intended to relate environmental change as well as anthropogenic influence to our outcome, two factors that are known to play an important role (Behling 1997, 1998, 2002; Behling et al. 2004; Belsky 1992; Prieto 1996; Safford 2001; Vigglizzo and Frank 2006). As a particular question we analyzed the development of the Campos grasslands. We want to give a more detailed insight into the yet unsolved issue of the origin of the Campos, which is still under controversial discussion (Behling et al. 2004; Pinillos and Sarmiento, pers. comm). Based on our data we also want to investigate whether there is a tendency in grain size parameters to vary along an elevational gradient in the Paramo of samples of about the same age. The PleistoceneHolocene transition will be investigated based on the data from the Campos in southern Brazil as well as the dynamics during the Holocene before and after the onset of human activities. Human activities as well as climate change are driving forces for vegetation change, which are very evident in common palynological analyses. C (...truncated)