An analysis of phytolith assemblages for the quantitative reconstruction of late Quaternary environments of the Lower Taieri Plain, Otago, South Island, New Zealand I. Modern assemblages and transfer functions

Abstract

An analysis of modern phytolith assemblages is presented. Phytolith assemblages were studied in modern surface soils and sediments of 28 sites from east Otago, New Zealand, within a range of vegetation types and microclimates. No simple distinction could be made between vegetation types on the basis of phytolith assemblage composition. A Principal Components Analysis (PCA) of the phytolith data set revealed that festucoid, chloridoid and spherical phytolith morphotypes formed strong associations with sites from wetland, grassland, and forest vegetation types, respectively. More importantly, a comparison of sample replicates from each field site using Squared Chord Distance (SCD) assemblage analysis showed that wetland and grassland sites tended to produce more internally consistent phytolith assemblages than forest sites. Environmental variables including pH, conductivity, altitude, precipitation and temperature were also gathered for each site. The ability of each environmental variable to reflect variance in the entire phytolith data set was estimated by a series of Redundancy Analyses (RDA) with Monte Carlo permutation tests of statistical significance. After a forward selection process, transfer functions were generated using Partial Least Squares (PLS) regression and calibration with jack-knife validation. The final transfer functions have root mean squared errors of prediction for pH (0.47), log conductivity (0.38 mS cm), average annual precipitation (63 mm), and average annual (0.28 8C), spring (0.38 8C) and autumn temperature (0.41 8C); the smallest group of environmental variables explaining the most variance in the modern phytolith data set. The most useful transfer functions for application to fossil phytolith data and paleoenvironmen- tal interpretation are pH, log conductivity and annual precipitation. The relationship between changes in pH and annual precipitation and phytolith assemblage composition found in this study presents a prima facie relationship with the potential to provide direct proxies for soil weathering and indirectly for paleoenvironmental reconstruc- tion.