Doctor Aimee Bourne

Candidature

Aimee Bourne Graduated PhD 2016

Thesis Title

Forest ecosystem water use: does species identity and ecosystem composition matter?

Research Project

Australia's native forests and woodlands are biologically diverse, yet in large-scale tree-plantings for reforestation we still use species monocultures according to traditional forestry practices. While forest water-use and susceptibility to drought are key concerns in plantation establishment and management in Australia, we have little understanding of how water-use or drought tolerance of plantations is affected by tree species diversity. It is commonly assumed that forest water-use per unit leaf area of trees is independent of species identity and diversity, despite evidence that species can differ significantly in the dynamics of water-use in relation to environment.

Transpiration accounts for a large portion of water loss from land surfaces and dominates the loss of water from vegetated ecosystems. To date there is no study which has experimentally addressed the relationship between species diversity and stand water-use. There is still no consistent framework for estimating the contribution of individual species or species groups to whole plantation or ecosystem water-use. Understanding the magnitude of water losses from ecosystems and how they affect water balance is crucial to future planning in Australia in regards to catchment management, water conservation and adaptation potential to climate change.

I aim to address this issue using model ecosystems of native Australian tree species with a range of different ecological characteristics. These model ecosystems will be grown in a progression of species richness from single-species monocultures (Eucalyptus crebra and E. tereticornis) to 2- and 4-species (E. elata and E. fibrosa) mixtures to overall species-rich plots containing 8 tree species representing reconstructed native ecosystems. Water-use of these forested ecosystems will be measured using the Heat Ratio Method (HRM) and soil moisture sensors. Preliminary data for species monocultures suggests that there are differences in the canopy conductance response to vapour pressure deficit (environmental variation) of E. crebra and E. tereticornis. These species are the major focal species of this study, representing 'drought-tolerant' and 'drought-avoiding' species respectively.

Research Project Photos

Photos relate to Diversity Plantation (planted 2011) and Common Garden (established 2007 at HFE).

Diversity Plantations Spare potted plants Common Garden (3 years old)


Diversity Plantations - 1 day after planting	These plantations contain monoculture, irrigated mixture, unirrigated mixture and diverse plots
Spare Potted Plants - 8 different species	The 8 species planted including Eucalyptus crebra, E. tereticornis (focal species), E. fibrosa, E. elata, Angophora subvelutina, A. floribunda, Melia azedarach and Melaleuca linariifolia
Common Garden - at 3 years planting	The Common Garden is planted at the Hawkesbury Forest Experiement (HFE) site and contains 7 different species of Eucalypt. Each plot is a monoculture of a different Eucalyptus species.

Leaf form in eucalypts Mature Euc leaves Measuring tree heights

Leaf form in eucalypts	Juvenile leaves of the different species planted in the Common Garden
Mature Euc leaves of different species, stomatal density peels	Leaves of different Eucalypt species prepared for stomatal density peels
Measuring tree heights	Measuring tree height in a Eucalypt monoculture

Crebra - one of the focal species HRM sapflow probe in Euc tree

Crebra - one of the focal species	Eucalyptus crebra, one of the focal species of this study
HRM sapflow probe in Euc tree	Heat Ration Method (HRM) sapflow probes - one of the methods being used to assess tree water use in the common garden

Research Project Supervisors

Professor David Ellsworth, Dr Tony Haigh, Dr Brendan Choat

Awards/Honours

Awarded best inaugural presentation by a student at the Ecological Society of Australia Conference, Melbourne, 2012
Judged best oral presentation (and $50) in session 1E "Environmental Ecology" at the School of Science and Health Research Staff and HDR Research Showcase - 2012
Awarded 2nd place and $500 towards her candidature in the Three Minute Thesis Competition for the HDR presentation 'Species diversity effects on forest ecosystem water-use'. Aimee was one of three who represented the College of Health and Science in the UWS wide competition - 2011

Publications

Choury Z, Wujeska-Klause A, Bourne A, Bown NP, Tjoelker MG, Medlyn BE, Crous KY, (2022) 'Tropical rainforest species have larger increases in temperature optima with warming than warm-temperate rainforest trees', New Phytologist, vol.234, no.4, pp 1220-1236

Bourne AE, Creek D, Peters JMR, Ellsworth DS, Choat B, (2017) 'Species climate range influences hydraulic and stomatal traits in Eucalyptus species', Annals of Botany, vol.120, no.1, pp 123-133

Bourne AE, Haigh AM, Ellsworth DS, (2015) 'Stomatal sensitivity to vapour pressure deficit relates to climate of origin in Eucalyptus species', Tree Physiology, vol.35, no.3, pp 266-278

Héroult A, Lin Y-S, Bourne A, Medlyn BE, Ellsworth DS, (2013) 'Optimal stomatal conductance in relation to photosynthesis in climatically contrasting Eucalyptus species under drought', Plant, Cell and Environment, vol.36, no.2, pp 262-274