Abstract
The aboveground architecture of Eucalyptus marginata (Jarrah) was investigated in chronosequences of young trees (2.5, 5 and 10 m height) growing in a seasonally dry climate in a natural forest environment with intact soils, and on adjacent restored bauxite mine sites on soils with highly modified A and B horizons above an intact C horizon. Compared to forest trees, trees on restored sites were much younger and faster growing, with straighter, more clearly defined main stems and deeper, narrower crowns containing a greater number of branches that were longer, thinner and more vertically angled. Trees on restored sites also had a higher fraction of biomass in leaves than forest trees, as indicated by 20-25% thicker leaves, 30-70% greater leaf area, 10-30% greater leaf area to sapwood area ratios and 5-30% lesser branch Huber values. Differences in crown architecture and biomass distribution were consistent with putatively greater soil-water, nutrient and light availability on restored sites. Our results demonstrate that under the same climatic conditions, E. marginata displays a high degree of plasticity of aboveground architecture in response to the net effects of resource availability and soil environment. These differences in architecture are likely to have functional consequences in relation to tree hydraulics and growth that, on larger scales, is likely to affect the water and carbon balances of restored forest ecosystems. This study highlights substrate as a significant determinant of tree architecture in water-limited environments. It further suggests that the architecture of young trees on restored sites may need to change again if they are to survive likely longer-term changes in resource availability.
Highlights
Aboveground architecture is a major determinant of tree function through its effects on leaf-scale physiological processes such as photosynthesis and transpiration (e.g., Hubbard et al 2001), which in turn contribute strongly to larger-scale ecosystem characteristics such as carbon and water balances
The Jarrah forest is a tall, dry sclerophyll open forest dominated by E. marginata (Jarrah) and Corymbia calophylla (Marri)
Leaves of trees on restored sites were 20–25% thicker than leaves of forest trees, but growth environment had no effect on the size of individual leaves as measured by area (Figure 1A and B; Table 2)
Summary
Aboveground architecture is a major determinant of tree function through its effects on leaf-scale physiological processes such as photosynthesis and transpiration (e.g., Hubbard et al 2001), which in turn contribute strongly to larger-scale ecosystem characteristics such as carbon and water balances. One of the most plastic of all tree genera is Eucalyptus, and in wild populations in Australia, it is difficult to find even two eucalypts of the same species identical in shape and structure. Eucalyptus is a commercially and environmentally important genus worldwide and there is a growing need to understand the ‘plasticity’ of eucalypt architecture in natural and managed environments, especially as it relates to physiological processes such as water and carbon gain. Most of our knowledge of Eucalyptus architecture comes from the studies of species in managed plantations, where both genotypic and environmental influences on architecture are routinely manipulated to meet commercial objectives. In semi-arid riparian ecosystems, naturally occurring E. camaldulensis is characterized by a short, thick bole and a large, irregularly
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