title: Does stream flow structure woody riparian vegetation in subtropical catchments?
abstract: The primary objective of this study was to test the relevance of hydrological classification and class differences to the characteristics of woody riparian vegetation in a subtropical landscape in Queensland, Australia. We followed classification procedures of the environmental flow framework ELOHA - Ecological Limits of Hydrologic Alteration. Riparian surveys at 44 sites distributed across five flow classes recorded 191 woody riparian species and 15, 500 individuals. There were differences among flow classes for riparian species richness, total abundance, and abundance of regenerating native trees and shrubs. There were also significant class differences in the occurrence of three common tree species, and 21 indicator species (mostly native taxa) further distinguished the vegetation characteristics of each flow class. We investigated the influence of key drivers of riparian vegetation structure (climate, depth to water table, stream-specific power, substrate type, degree of hydrologic alteration, and land use) on riparian vegetation. Patterns were explained largely by climate, particularly annual rainfall and temperature. Strong covarying drivers (hydrology and climate) prevented us from isolating the independent influences of these drivers on riparian assemblage structure. The prevalence of species considered typically rheophytic in some flow classes implies a more substantial role for flow in these classes but needs further testing. No relationships were found between land use and riparian vegetation composition and structure. This study demonstrates the relevance of flow classification to the structure of riparian vegetation in a subtropical landscape, and the influence of covarying drivers on riparian patterns. Management of environmental flows to influence riparian vegetation assemblages would likely have most potential in sites dominated by rheophytic species where hydrological influences override other controls. In contrast, where vegetation assemblages are dominated by a diverse array of typical rainforest species, and other factors including broad-scale climatic gradients and topographic variables have greater influence than hydrology, riparian vegetation is likely to be less responsive to environmental flow management.
authors.affiliation: Australian Rivers Institute Griffith University Nathan Qld 4111 Australia; Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER) James Cook University Townsville Qld 4811 Australia.
authors.forename: Cassandra S
authors.initials: CS
authors.lastname: James
authors.affiliation: Australian Rivers Institute Griffith University Nathan Qld 4111 Australia; Department of Natural Resources and Mines Water Services PO Box 5318 Townsville Qld 4810 Australia.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Mackay
authors.affiliation: Australian Rivers Institute Griffith University Nathan Qld 4111 Australia.
authors.forename: Angela H
authors.initials: AH
authors.lastname: Arthington
authors.affiliation: Australian Rivers Institute Griffith University Nathan Qld 4111 Australia.
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Capon
authors.affiliation: Australian Rivers Institute Griffith University Nathan Qld 4111 Australia.
authors.forename: Anna
authors.initials: A
authors.lastname: Barnes
authors.affiliation: Hydrobiology Pty Ltd Toowong Qld 4066 Australia.
authors.forename: Ben
authors.initials: B
authors.lastname: Pearson
keywords: ELOHA; environmental flows; flood disturbance; hydrological modification; plant ecology; riparian forests; river management