Towards understanding the fossil record better: insights from recently deposited plant macrofossils in a sclerophyll-dominated subalpine environment

Accumulations of plant macrofossils in lake sediments and other sedimentary deposits are increasingly being used to refine our understanding of past vegetation history, ecological processes and related climate conditions. However, past vegetation studies based on the use of disarticulated plant structures need to consider the specific potential for fossilisation of different species and different plant organs. Such knowledge is available for many systems, but the taphonomy of sclerophyll floras is very poorly known.

To provide understanding of the taphonomic processes affecting the representation of sclerophyllous plant species in fossil assemblages this study investigated the potential source vegetation of plant remains extracted from modern sediments of a subalpine lake in Tasmania, southernmost Australia. It was found that the vast majority of the leaf types represented in the sediments belong to broadleaf sclerophyllous species living in close proximity to the lake, although the representation of species was not related to their values of leaf mass per unit area.

Additionally, a bias between the abundance of species in the standing vegetation and the number of leaves of the same species in sediments was observed. Thus, small-leaved shrub species, such as many members of Ericaceae, produce comparatively many more leaves and tend to be over-represented in sediments. In contrast, even though, large-leaved tree species such as Eucalyptus and Nothofagus are dominant in the standing vegetation, they produce substantially fewer foliar organs per ground area of vegetation.

Accounting for these discrepancies, we developed an intrinsic representativity index that provides a more accurate picture of the relationship between the leaf assemblages incorporated in the sediments and the abundance of these species in the source vegetation.