Differentiating vegetation and environmental conditions using soil phytolith assemblages: insights from a bioclimatic gradient across northern Australia

Abstract Background and Aims Analysis of fossil phytolith assemblages from palaeoecological and archaeological sites relies on the development of robust modern reference material from soils. This study investigates the utility of soil phytolith assemblages for characterising vegetation and environmental conditions across northern Australia and develops new validated phytolith indices for palaeoenvironmental reconstruction. Methods Phytoliths were extracted from 29 surface soil samples from ten vegetation types across a latitudinal bioclimatic gradient of northern Australia. Soil phytolith assemblages were compared with vegetation survey data and bioclimatic and edaphic variables. Redundancy analysis, linear discriminant analysis, and correlation analyses were used to explore relationships and evaluate the discriminatory power of environmental variables and morphotypes. Finally, the effectiveness of commonly used and proposed regional phytolith indices is evaluated. Results Soil phytolith assemblages broadly represent overlying vegetation communities but more clearly capture regional bioclimatic patterns. Statistical analyses reveal that assemblage composition is primarily driven by the latitudinal precipitation gradient, with Panicoideae phytoliths showing a promising positive correlation with mean annual precipitation. Two proposed phytolith indices (Iws and NA Ip) outperform the commonly used D:P ratio and Iph index and show strong potential for reconstruction of bioclimatic conditions. Conclusions This study demonstrates the potential of phytoliths to characterise vegetation and climatic patterns in northern Australia. Soil phytolith assemblages reflect changes in grass community composition and tree cover associated with the latitudinal precipitation gradient, and the proposed indices provide a framework for detecting past environmental variability. These findings highlight the utility of phytoliths for palaeoenvironmental research across northern Australia.