Variations in Populations of Eucalyptus ovata Labill., And the Effects of Waterlogging on Seedling Growth

Abstract

Techniques of classification and ordination were used to describe the pattern of variation in tree form and leaf, fruit and seedling morphology found in four southern Victorian populations, referred to as Eucalyptus ovata (swamp gum), from sites differing in mean annual rainfall, soil type and severity of waterlogging. Trees from sites with higher mean annual rainfall were large in stature (33 + m) and smooth-trunked with a variable amount of flaky bark at the base. Fruits were typical of E. ovata in shape, although their size, and that of leaves, varied from west to east from relatively large to small. In drier coastal areas in western Victoria trees may be short (5 m), multi-stemmed, large-fruited and small-leaved compared with the more common, and typical, open-forest form of the species.

Seedlings from the tall open-forest forms grew rapidly, developed distinctly square stems and broad lanceolate to cordate leaves which were opposite and sessile at least to the 10th node, and had a low frequency of lignotuber development. In contrast, seedlings from open-forest forms of lower rainfall areas, and particularly from waterlogged sites, were slower-growing and morphologically more typical of the species, having round stems, oval leaves which were petiolate and alternating at the 10th node, and lignotubers.

Waterlogging reduced seedling yield, leaf size and lignotuber development. All populations responded similarly to waterlogging treatment and typical responses included development of stem hypertrophy and adventitious roots which were often negatively geotropic.

The pattern of variation observed in southern Victoria may reflect ecotypic differentiation, although the source of that genetic information may have been the result of past hybridization, perhaps with E. cypellocarpa or E. viminalis depending on locality.