Growth characteristics of Eucalyptus camaldulensis trees differ between adjacent regulated and unregulated rivers in semi-arid temperate woodlands

Abstract

River red gum (Eucalyptus camaldulensis) is the most widely-distributed eucalypt, an important timberresource, and critical to the sustainable function of many Australian waterways. Agricultural develop-ment, including decades of river regulation, has resulted in extensive degradation ofE. camaldulensiswoodlands, and restoration is now required to maintain ecological function in many floodplain areas.To aid restoration planning, we quantified the structural characteristics ofE. camaldulensistrees in anintensively farmed region of eastern Australia. We studied tree populations on two rivers with differenthydrological regimes: (1) Bogan River - ephemeral and surrounded by dryland agriculture, and (2)Macquarie River - permanent and the focus of irrigated agriculture. The two populations showed cleardifferences in allometric relationships. Trees on the ephemeral river were shorter with relatively widercanopies than trees with similar stem diameter on the permanent river. Trees on the ephemeral river pro-gressed through stages of senescence at smaller stem sizes than those on the permanent river. Treegrowth was episodic and strongly related to tree senescence, but the amount of growth in stem diameterwas less on the ephemeral river. Tree senescence and stem diameter had the strongest effects on theprobability of trees bearing hollows, with a lesser interactive effect of river hydrology. Variation amongindividual trees, sites and sub-catchments was large and not fully explained by the site characteristicsmeasured. Our data enable predictions of future vegetation growth and fauna habitat development insemi-arid riparian woodlands that are not managed for silvicultural production. Our findings indicatethat differences in the hydrological regimes of inland rivers manifest as differences in structural attri-butes ofE. camaldulensis, even among individuals occupying the same catchment management area.Such differences should be reflected in future management strategies to sustain the function and biodi-versity of riparian forests and woodlands