Vegetation-radiation relationships in mountainous terrain: eucalypt-dominated vegetation in the Risdon Hills, Tasmania

The vegetation along a north-south transect across a valley in the Risdon Hills, Tasmania, varies from Eucalyptus globulus-E. viminalis-E. amygdalina open-forest with a dense understorey of broad-leaved shrubs to E. Risdonii open-scrub with a sparse understorey of sclerophyll shrubs and graminoids. The variation in vegetation along the transect is highly correlated with total annual solar radiation, calculated to include the effects of shading, cloud cover and the sky view factor. The distributions of a large proportion of the species found along the transect are most highly significantly correlated with the solar radiation received in one of the solstice months. However, the response of most species to variation in incident solar radiation is curvilinear rather than linear. The topographically driest site does not possess the most xeric vegetation. This deflection is probably a consequence of downslope movement of soil moisture and runoff. Also, the most xeric vegetation tends to occur on northwest rather than north-facing slopes, possibly a result of an evapotranspiration peak in late afternoon.