Abstract – Dr. David Greenwood

Dr. David Greenwood, Department of Biology, Brandon University

Abstract

Recent climate modelling and proxy analyses highlighted the importance of precipitation in Eocene warm ice-free high latitude climates. Leaf area analysis (LAA) is a proxy based on a correlation between mean leaf-area of woody dicot species in modern western hemisphere forests (i.e., Laurasia), and mean annual precipitation (MAP). Eocene and Miocene climate model-proxy comparisons of precipitation have used palaeobotanical proxies such as LAA to estimate MAP for fossil sites in the Arctic, North America, South America, and Australia. However, recent regional and global analyses of leaf physiognomy indicated that some leaf traits (e.g. leaf teeth) are associated with selected angiosperm clades, implying a role for biogeographical or phylogenetic history in determining regional climate-leaf physiognomic relationships. We examined 101 Australian tropical seasonally-dry to humid forest sites (MAP 47–438 cm a^-1; mean annual temperature 18–28°C) to assess (1) whether these forests occupy the same leaf-climate space as the original LAA calibration or that the Australian forests’ leaf size-MAP relationship reflected their separate biogeographical history as a gondwanan flora, and (2) the role of leaf life-span and seasonality. An additional 28 sites were analysed from South Africa and Fiji, also gondwanan floras. Our data show that the Australian and Fijian tropical seasonally-dry deciduous to humid evergreen forests: (1) fall within the same leaf-climate space as the original western hemisphere LAA calibration; (2) the wettest evergreen forests (MAP ≥ 200 cm a^-1, driest quarter ≥ 15 cm) display fewer large-leafed species than expected from the western hemisphere calibration; and (3) precipitation seasonality affects leaf-size precipitation relationships with wet-season precipitation a better predictor of mean leaf size than MAP. Further, analysis of the South African sites shows: (4) moist forest sites plot within the same leaf-climate space as the combined western hemisphere and Australian data sets; (5) water stressed nutrient-poor Fynbos sites – a markedly sclerophyllous vegetation type – exhibit smaller leaf sizes than expected (but consistent with Australian data), reflecting the predominantly evergreen character of these communities.