title: Functional trait variation along a hydrological gradient and trait-based predictions of the composition of a wetland plant community

authors: Purcell, Adam

subjects: functional trait

abstract: Predicting the assembly of plant communities is considered the Holy Grail of functional ecology and has never been more important as we head into an era of environmental change. Studying plant functional traits provides the best opportunity for understanding the community assembly processes that determine the abundance and distribution of plant species. Plant functional traits provide information on the direct physiological adaptations of plants to various environmental conditions. The assembly of plant communities is driven by filtering processes that select for or against certain functional traits and a plant can only be present within a community if it contains the functional traits necessary to germinate, survive and compete in the environment of the community. An understanding of how functional traits are filtered by the environment and biotic interactions provides the foundations for predictive community assembly models. However, the understanding of how functional traits are filtered along hydrological gradients is poor for the majority of functional traits. 
In this thesis I aimed to identify how plant functional traits respond to variation in soil hydrology in the presence and absence of grazing and determine whether a trait-based model of environmental filtering could predict the composition of an ephemeral wetland plant community. To achieve these aims, I performed a survey of the plant community in an ephemeral wetland in grazed and ungrazed transects. The survey was conducted along a hydrological gradient that was split into an elevation gradient above the flood line and a flooding gradient below the flood line. I measured nine root, leaf and shoot traits on 885 plant samples collected during the community survey and investigated the response of community-weighted and individual-level traits along the hydrological gradient using Generalized Additive Models (GAMs) and Generalized Linear Models (GLMs). To determine whether a trait-based model of environmental filtering could predict the composition of the plant community, I incorporated the individual-level trait relationships into a community assembly model known as Traitspace and predicted the relative abundance of the 23 most common species found within the Kettlehole.
Community-weighted root traits were more strongly related to the hydrological gradient than aboveground traits. Root aerenchyma increased as the number of days submerged increased while root dry matter content (RDMC), specific root length (SRL), root tissue density (RTD) and root branching intensity (RBI) decreased with increasing flooding. Community-weighted specific leaf area (SLA) and root tissue density were more closely related to the elevation gradient than any other traits. SLA decreased as elevation above the flood line increased while RTD increased with elevation. The relationships between individual-level traits and the elevation and flooding gradients were far weaker than community-weighted traits but showed similar trends in the directions of trait responses along the gradients. Grazing reduced the community-weighted trait values of all traits except SLA and aboveground dry matter content (AGDMC) along the flooding gradient and had little effect on the trait values observed along the elevation gradient.
Using environmental filtering of functional traits, the Traitspace model was able to predict the distribution and abundance of a number of key species within the wetland plant community but was unable to accurately predict the abundance and distribution of other species. The accuracy of the Traitspace model was best when all nine functional traits were used to produce predictions of species abundances but SLA and height were recognised as the two traits to provide the most predictive ability.
The strong filtering of root traits illustrate the important information that root traits provide in terms of the adaptations of plants in environments with varied soil hydrology. Easily measurable aboveground traits are often favoured in functional ecology but these results highlight the importance of measuring root traits in trait-based research. Traitspace has the ability to predict the abundance and distribution of some species within a wetland plant community using environmental filtering of functional traits. Community assembly at small spatial scales is mostly driven by biotic interactions rather than environmental filtering which may limit the power of current predictive models. The inclusion of biotic interactions into trait-based models will improve the predictions of community composition at small spatial scales in wetland ecosystems and help us to progress towards achieving the goal of accurately predicting the composition of plant communities.

text: Functional trait variation along a hydrological gradient and trait-based predictions of the composition of a wetland plant community Predicting the assembly of plant communities is considered the Holy Grail of functional ecology and has never been more important as we head into an era of environmental change. Studying plant functional traits provides the best opportunity for understanding the community assembly processes that determine the abundance and distribution of plant species. Plant functional traits provide information on the direct physiological adaptations of plants to various environmental conditions. The assembly of plant communities is driven by filtering processes that select for or against certain functional traits and a plant can only be present within a community if it contains the functional traits necessary to germinate, survive and compete in the environment of the community. An understanding of how functional traits are filtered by the environment and biotic interactions provides the foundations for predictive community assembly models. However, the understanding of how functional traits are filtered along hydrological gradients is poor for the majority of functional traits. 
In this thesis I aimed to identify how plant functional traits respond to variation in soil hydrology in the presence and absence of grazing and determine whether a trait-based model of environmental filtering could predict the composition of an ephemeral wetland plant community. To achieve these aims, I performed a survey of the plant community in an ephemeral wetland in grazed and ungrazed transects. The survey was conducted along a hydrological gradient that was split into an elevation gradient above the flood line and a flooding gradient below the flood line. I measured nine root, leaf and shoot traits on 885 plant samples collected during the community survey and investigated the response of community-weighted and individual-level traits along the hydrological gradient using Generalized Additive Models (GAMs) and Generalized Linear Models (GLMs). To determine whether a trait-based model of environmental filtering could predict the composition of the plant community, I incorporated the individual-level trait relationships into a community assembly model known as Traitspace and predicted the relative abundance of the 23 most common species found within the Kettlehole.
Community-weighted root traits were more strongly related to the hydrological gradient than aboveground traits. Root aerenchyma increased as the number of days submerged increased while root dry matter content (RDMC), specific root length (SRL), root tissue density (RTD) and root branching intensity (RBI) decreased with increasing flooding. Community-weighted specific leaf area (SLA) and root tissue density were more closely related to the elevation gradient than any other traits. SLA decreased as elevation above the flood line increased while RTD increased with elevation. The relationships between individual-level traits and the elevation and flooding gradients were far weaker than community-weighted traits but showed similar trends in the directions of trait responses along the gradients. Grazing reduced the community-weighted trait values of all traits except SLA and aboveground dry matter content (AGDMC) along the flooding gradient and had little effect on the trait values observed along the elevation gradient.
Using environmental filtering of functional traits, the Traitspace model was able to predict the distribution and abundance of a number of key species within the wetland plant community but was unable to accurately predict the abundance and distribution of other species. The accuracy of the Traitspace model was best when all nine functional traits were used to produce predictions of species abundances but SLA and height were recognised as the two traits to provide the most predictive ability.
The strong filtering of root traits illustrate the important information that root traits provide in terms of the adaptations of plants in environments with varied soil hydrology. Easily measurable aboveground traits are often favoured in functional ecology but these results highlight the importance of measuring root traits in trait-based research. Traitspace has the ability to predict the abundance and distribution of some species within a wetland plant community using environmental filtering of functional traits. Community assembly at small spatial scales is mostly driven by biotic interactions rather than environmental filtering which may limit the power of current predictive models. The inclusion of biotic interactions into trait-based models will improve the predictions of community composition at small spatial scales in wetland ecosystems and help us to progress towards achieving the goal of accurately predicting the composition of plant communities.

year: 2016

title: Carbonate Alteration of the Sams Creek Gold Deposit

authors: Lee, Ryan John

subjects: Sams Creek Gold Depsoit

abstract: Located near Upper Takaka, NW Nelson, the Sams Creek Gold Deposit is host to significant gold mineralisation, which has been extensively explored since being first discovered in 1974 by CRA exploration. The gold mineralisation, hosted largely within the Sams Creek Granite Dyke has since been the focus of continual ongoing exploration and research by various companies and academia. The dyke is a peralkaline microgranite, is up to 60 meters wide and has a strike length totalling 7 kilometres. Multiple stages of hydrothermal alteration have affected the granite dyke which is host to a series of sheeted, stock work and irregular fracture veins. At the time of writing, Sams Creek is New Zealand’s largest undeveloped gold project.

Despite extensive research and exploration, the origin of Au bearing fluids and hence classification of the deposit is still debated. Little is also known about the role of which the widespread carbonate alteration has had during the genesis of this deposit. Siderite/ankerite (carbonate) veins are a common occurrence at Sams Creek, occurring in both the highly mineralised granite and seemingly unaltered metasedimentary rock, of which the Sams Creek Granite and various other mafic dykes intrude.

This study presents a detailed paragenetic study of the multiple phases of carbonate alteration throughout the prospect. Trace element geochemistry for individual vein generations was obtained by in-situ analysis of the carbonate vein minerals using LA-ICP-MS. Oxygen and carbonate stable isotope ratios were also determined for many of the carbonate minerals.

The carbonate alteration was found to be largely structurally controlled and coeval with the multiple stages of Au mineralisation and alteration. The veins were often comprised of multiple siderite and ankerite intergrowths, reflecting temporally distinct fluids of varying Ca/Fe/Mn/Mg concentrations. Whole vein geochemical analysis confirmed an overall ankerite composition, contrary to the previous reports of siderite only veins. Major and trace element signatures showed geochemically distinct ankerite veins for each host rock. Notably, the geochemistry of the veins indicates that the surrounding metasediments are an unlikely fluid source for the carbonate alteration. This has implications for models which suggest an orogenic fluid is responsible for the alteration. The fluid likely received its trace element and isotopic signature from a high temperature, reduced and 18O-depleted fluid source, consistent with a fluid source that is not metamorphogenic. The carbonate minerals associated with the mineralisation and/or the dyke have a unique trace element signature in relation to carbonate of other lithologies.

Overall, this study provides evidence that is in agreement with the Sams Creek Dyke being classified as an Intrusion Related Gold System. Further implications for exploration potential are the distinctions between metamorphogenic and hydrothermal carbonate minerals, which could be easily undertaken using pXRF based upon anomalous Mn and Mg contents.

text: Carbonate Alteration of the Sams Creek Gold Deposit Located near Upper Takaka, NW Nelson, the Sams Creek Gold Deposit is host to significant gold mineralisation, which has been extensively explored since being first discovered in 1974 by CRA exploration. The gold mineralisation, hosted largely within the Sams Creek Granite Dyke has since been the focus of continual ongoing exploration and research by various companies and academia. The dyke is a peralkaline microgranite, is up to 60 meters wide and has a strike length totalling 7 kilometres. Multiple stages of hydrothermal alteration have affected the granite dyke which is host to a series of sheeted, stock work and irregular fracture veins. At the time of writing, Sams Creek is New Zealand’s largest undeveloped gold project.

Despite extensive research and exploration, the origin of Au bearing fluids and hence classification of the deposit is still debated. Little is also known about the role of which the widespread carbonate alteration has had during the genesis of this deposit. Siderite/ankerite (carbonate) veins are a common occurrence at Sams Creek, occurring in both the highly mineralised granite and seemingly unaltered metasedimentary rock, of which the Sams Creek Granite and various other mafic dykes intrude.

This study presents a detailed paragenetic study of the multiple phases of carbonate alteration throughout the prospect. Trace element geochemistry for individual vein generations was obtained by in-situ analysis of the carbonate vein minerals using LA-ICP-MS. Oxygen and carbonate stable isotope ratios were also determined for many of the carbonate minerals.

The carbonate alteration was found to be largely structurally controlled and coeval with the multiple stages of Au mineralisation and alteration. The veins were often comprised of multiple siderite and ankerite intergrowths, reflecting temporally distinct fluids of varying Ca/Fe/Mn/Mg concentrations. Whole vein geochemical analysis confirmed an overall ankerite composition, contrary to the previous reports of siderite only veins. Major and trace element signatures showed geochemically distinct ankerite veins for each host rock. Notably, the geochemistry of the veins indicates that the surrounding metasediments are an unlikely fluid source for the carbonate alteration. This has implications for models which suggest an orogenic fluid is responsible for the alteration. The fluid likely received its trace element and isotopic signature from a high temperature, reduced and 18O-depleted fluid source, consistent with a fluid source that is not metamorphogenic. The carbonate minerals associated with the mineralisation and/or the dyke have a unique trace element signature in relation to carbonate of other lithologies.

Overall, this study provides evidence that is in agreement with the Sams Creek Dyke being classified as an Intrusion Related Gold System. Further implications for exploration potential are the distinctions between metamorphogenic and hydrothermal carbonate minerals, which could be easily undertaken using pXRF based upon anomalous Mn and Mg contents.

year: 2016

title: Ki te kapu o taku ringa - In the palm of my hand [Photography exhibition at Gallagher Academy of Performing Arts]

authors: Hill, Rodrigo

subjects: Mātauranga Māori

abstract: (Exhibition catalogue)
The title Ki te kapu o taku ringa is taken from a line of
‘Maioha mō Waikato’ by Kīngi Tāwhiao. Ejected from their
homelands he and his Waikato brethren took refuge with
their Maniapoto relations in Te Nehenehenui. The maioha
was composed expressing Kīngi Tāwhiao’s love for his
homelands, and his solastalgic holding fast to those lands
‘... in the palm of his hand.’ The words from the song-poem
were used as guide to our research and photography practice.

text: Ki te kapu o taku ringa - In the palm of my hand [Photography exhibition at Gallagher Academy of Performing Arts] (Exhibition catalogue)
The title Ki te kapu o taku ringa is taken from a line of
‘Maioha mō Waikato’ by Kīngi Tāwhiao. Ejected from their
homelands he and his Waikato brethren took refuge with
their Maniapoto relations in Te Nehenehenui. The maioha
was composed expressing Kīngi Tāwhiao’s love for his
homelands, and his solastalgic holding fast to those lands
‘... in the palm of his hand.’ The words from the song-poem
were used as guide to our research and photography practice.

year: 2025