title: The reassembly of soil food web structure and functioning in restored urban forests across Aotearoa - New Zealand

authors: Rai, Bibishan

abstract: Soil food webs play a central role in the successful restoration of critical ecosystem processes. Yet, we lack an understanding of how these highly diverse and functionally complex belowground communities reassemble in forests undergoing restoration, and the factors responsible for varying trajectories of soil community reassembly. Even more poorly understood is the reassembly of soil invertebrates across multiple trophic levels after disturbance. Moreover, any potential effect of ecological succession on food web structural properties (connectance and maximum trophic level) and its implications on soil invertebrate trophic functions remains poorly understood. In this PhD thesis, I investigate the effect of restoration age and biotic and abiotic characteristics of restored forests on the reassembly of soil invertebrate communities across different trophic groups. I also explore the effect of the aforementioned predictors on soil food web structure and associated ecosystem functioning.
I sampled soil invertebrate communities from 70 urban restored forests, as well as three unrestored and three remnant urban forests. All forest sites were distributed across eight cities in Aotearoa, New Zealand and were historically occupied by native vegetation until cleared for either agriculture or urban development. The sites were then planted with native woody species between six and 60 years prior to this research, forming a chronosequence of forest succession. In addition to soil invertebrates, vegetation data (e.g., mean tree diameter, tree species richness) and site characteristics (e.g., litter depth, soil temperature) were also collected from these forests. I identified the soil invertebrates into major size-based functional groups (i.e., microfauna, mesofauna and macrofauna) and further into trophic levels: detritivores, fungivores, herbivores, omnivores and predators. Additionally, I quantified the abundance, biomass and mean body mass of all soil invertebrates. Finally, I constructed 70 local food webs across the restored forest sites and quantified the flux of energy between different feeding groups and their food sources to estimate five important ecosystem functions in soil food webs: detritivory, bacterivory, fungivory, herbivory and predation.
I analysed the relative importance of restored forest age and environmental variables as predictors of variation in soil invertebrate communities. I found that restoration age, in itself, had no discernible effect on the abundance, biomass or mean body size of soil invertebrate communities. Instead, site characteristics like mean tree diameter, tree species richness, litter depth and soil temperature were the main drivers of variability in soil communities. Notably, these factors influenced larger macrofauna and mesofauna more than nematodes. However, when I modelled the effects of restoration age on soil communities in a structural equation modelling framework, taking into account bottom-up effects from plant communities to invertebrate predators, restoration age was shown to have indirect effects on the biomass of mesofauna decomposers, omnivores and nematode predators. Finally, by investigating shifts in food web structure and resulting changes in energy fluxes across trophic levels, I found that forest restoration age did not directly influence either the structure (connectance, maximum trophic level) or the five examined trophic functions of the soil food webs. Instead, effects of forest restoration age occurred through changes in vegetation characteristics as forest succession progresses.
My results suggests that forest age is not a direct major driver of the reassembly of soil invertebrate communities. Instead, mean tree diameter, tree species richness, litter depth, and soil temperature play important roles in the process. My results show the significance of planting trees that can grow large, promoting species diversity and allowing leaf litter to accumulate naturally to support soil invertebrate community of different trophic functions. Through my results, I also show how the aforementioned vegetation characteristics can contribute to flow of energy in the soil food web. In addition to demonstrating how crucial food web structural properties are to energy flow via trophic interactions such as detritivory, fungivory and predation, this research also highlights the interconnectedness of above and belowground ecosystems. Taken together, my findings suggest that urban restoration efforts should focus on promoting these beneficial vegetation characteristics, alongside considering food web complexity, to optimize trophic functions performed by soil food webs.

text: The reassembly of soil food web structure and functioning in restored urban forests across Aotearoa - New Zealand Soil food webs play a central role in the successful restoration of critical ecosystem processes. Yet, we lack an understanding of how these highly diverse and functionally complex belowground communities reassemble in forests undergoing restoration, and the factors responsible for varying trajectories of soil community reassembly. Even more poorly understood is the reassembly of soil invertebrates across multiple trophic levels after disturbance. Moreover, any potential effect of ecological succession on food web structural properties (connectance and maximum trophic level) and its implications on soil invertebrate trophic functions remains poorly understood. In this PhD thesis, I investigate the effect of restoration age and biotic and abiotic characteristics of restored forests on the reassembly of soil invertebrate communities across different trophic groups. I also explore the effect of the aforementioned predictors on soil food web structure and associated ecosystem functioning.
I sampled soil invertebrate communities from 70 urban restored forests, as well as three unrestored and three remnant urban forests. All forest sites were distributed across eight cities in Aotearoa, New Zealand and were historically occupied by native vegetation until cleared for either agriculture or urban development. The sites were then planted with native woody species between six and 60 years prior to this research, forming a chronosequence of forest succession. In addition to soil invertebrates, vegetation data (e.g., mean tree diameter, tree species richness) and site characteristics (e.g., litter depth, soil temperature) were also collected from these forests. I identified the soil invertebrates into major size-based functional groups (i.e., microfauna, mesofauna and macrofauna) and further into trophic levels: detritivores, fungivores, herbivores, omnivores and predators. Additionally, I quantified the abundance, biomass and mean body mass of all soil invertebrates. Finally, I constructed 70 local food webs across the restored forest sites and quantified the flux of energy between different feeding groups and their food sources to estimate five important ecosystem functions in soil food webs: detritivory, bacterivory, fungivory, herbivory and predation.
I analysed the relative importance of restored forest age and environmental variables as predictors of variation in soil invertebrate communities. I found that restoration age, in itself, had no discernible effect on the abundance, biomass or mean body size of soil invertebrate communities. Instead, site characteristics like mean tree diameter, tree species richness, litter depth and soil temperature were the main drivers of variability in soil communities. Notably, these factors influenced larger macrofauna and mesofauna more than nematodes. However, when I modelled the effects of restoration age on soil communities in a structural equation modelling framework, taking into account bottom-up effects from plant communities to invertebrate predators, restoration age was shown to have indirect effects on the biomass of mesofauna decomposers, omnivores and nematode predators. Finally, by investigating shifts in food web structure and resulting changes in energy fluxes across trophic levels, I found that forest restoration age did not directly influence either the structure (connectance, maximum trophic level) or the five examined trophic functions of the soil food webs. Instead, effects of forest restoration age occurred through changes in vegetation characteristics as forest succession progresses.
My results suggests that forest age is not a direct major driver of the reassembly of soil invertebrate communities. Instead, mean tree diameter, tree species richness, litter depth, and soil temperature play important roles in the process. My results show the significance of planting trees that can grow large, promoting species diversity and allowing leaf litter to accumulate naturally to support soil invertebrate community of different trophic functions. Through my results, I also show how the aforementioned vegetation characteristics can contribute to flow of energy in the soil food web. In addition to demonstrating how crucial food web structural properties are to energy flow via trophic interactions such as detritivory, fungivory and predation, this research also highlights the interconnectedness of above and belowground ecosystems. Taken together, my findings suggest that urban restoration efforts should focus on promoting these beneficial vegetation characteristics, alongside considering food web complexity, to optimize trophic functions performed by soil food webs.

year: 2024-09-02

title: Impact of elevated levels of CO2 on animal mediated ecosystem function: The modification of sediment nutrient fluxes by burrowing urchins

authors: Widdicombe, S.

subjects: Bioturbation

abstract: A mesocosm experiment was conducted to quantify the relationships between the presence and body size of two burrowing heart urchins (Brissopsis lyrifera and Echinocardium cordatum) and rates of sediment nutrient flux. Furthermore, the impact of seawater acidification on these relationships was determined during this 40-day exposure experiment. Using carbon dioxide (CO ₂) gas, seawater was acidified to pH NBS 7.6, 7.2 or 6.8. Control treatments were maintained in natural seawater (pH ≈ 8.0). Under normocapnic conditions, burrowing urchins were seen to reduce the sediment uptake of nitrite or nitrate whilst enhancing the release of silicate and phosphate. In acidified (hypercapnic) treatments, the biological control of biogeochemical cycles by urchins was significantly affected, probably through the combined impacts of high CO ₂ on nitrifying bacteria, benthic algae and urchin behaviour. This study highlights the importance of considering biological interactions when predicting the consequences of seawater acidification on ecosystem function.

text: Impact of elevated levels of CO2 on animal mediated ecosystem function: The modification of sediment nutrient fluxes by burrowing urchins A mesocosm experiment was conducted to quantify the relationships between the presence and body size of two burrowing heart urchins (Brissopsis lyrifera and Echinocardium cordatum) and rates of sediment nutrient flux. Furthermore, the impact of seawater acidification on these relationships was determined during this 40-day exposure experiment. Using carbon dioxide (CO ₂) gas, seawater was acidified to pH NBS 7.6, 7.2 or 6.8. Control treatments were maintained in natural seawater (pH ≈ 8.0). Under normocapnic conditions, burrowing urchins were seen to reduce the sediment uptake of nitrite or nitrate whilst enhancing the release of silicate and phosphate. In acidified (hypercapnic) treatments, the biological control of biogeochemical cycles by urchins was significantly affected, probably through the combined impacts of high CO ₂ on nitrifying bacteria, benthic algae and urchin behaviour. This study highlights the importance of considering biological interactions when predicting the consequences of seawater acidification on ecosystem function.

year: 2012

title: 'No-body' is my friend: Cultural considerations of young children's 'imaginary companions'

authors: Hayes (Bluett), Shilo Jane

subjects: imaginary companions

abstract: The variegated relationships young children may have during their early childhood education (ECE) years have long been of interest to theorists and teachers alike.  Relationships, and understandings of companionship, can take multiple forms. Our understandings of what these relationships may look like are frequently informed by complex social and cultural constructs; therefore, seeking to apply a one-size-fits-all interpretation is theoretically and culturally problematic, especially when the companions young children may spend time with may be unseen or unnoticed by surrounding adults.
A common Euro-western notion is that unseen companions are not real; hence they are generally referred to in the literature as being imaginary.  In an extensive literature review, this thesis explores whether companionship with the unseen are one of many possible forms of relationships.  Dominant Euro-western claims that such relationships are imaginary are considered critically before the analysis widens in theoretical scope to draw on various alternative cultural accounts.  The analysis draws on the theoretical work of Jacques Derrida, Michel Foucault and Karen Barad, in particular.  An additional exploration considers the author’s own situated experiences of parenting a child who during her childhood years had companions that were unseen to the author.  The final analysis, based on a small selection of carefully chosen autoethnographic accounts, draws on the significance of ancestral inheritance. Within this specific research context that inheritance comprises my daughter’s Māori ancestry and our shared Celtic ancestry. 
Ancestral inheritance provides reflexive companionship for the entire thesis.  Examining inheritance sheds light on ways that traditional Euro-western claims of the imagined worlds of children, and consequently childhood, have produced a legacy of ideas which have subsequently held the term imaginary in place.  These dominant worldviews are shown to fall short in their capacity to cover the diversity of lived realities of children and their unseen (to others) companion(s).  Inheritance also denotes the culturally mediated birthright that may travel alongside a young child and how this birthright may provide insight and alternative cultural knowledge and understandings of various multiform relationship companions.
As a result of analysing several possible perspectives on the relationships under study, this thesis proposes the new term culturally compatible travelling companions (CCTC): companions who travel alongside children as ordinary, expected features of their lifespan.  This shift in term acknowledges that diverse notions of companionship, and the forms this may take, are integral and salient constructions of each culture’s historical and narrative accounts.  
This is timely research, as currently nearly 64% of young children aged between birth and four years of age attend some type of Early Childhood Education (ECE) service in Aotearoa New Zealand (Ministry of Education [MoE], 2019).  The national ECE curriculum document Te Whāriki (MoE, 2017) recognises the significance of young children’s relationships and understands those relationships within the rich and complex cultural knowledge patterning that travels alongside a young child.  
The aim of this research is to add to the theoretical understandings of the forms, functions and features of the multiple, complex relationship companions who may share the lives of young children, whether or not these companions are seen or discernible to those around the children.  It suggests an alternative perspective to the dominant view and offers provocations for those who work alongside young children to think differently about whether these relationship companions are indeed only imaginary.

text: 'No-body' is my friend: Cultural considerations of young children's 'imaginary companions' The variegated relationships young children may have during their early childhood education (ECE) years have long been of interest to theorists and teachers alike.  Relationships, and understandings of companionship, can take multiple forms. Our understandings of what these relationships may look like are frequently informed by complex social and cultural constructs; therefore, seeking to apply a one-size-fits-all interpretation is theoretically and culturally problematic, especially when the companions young children may spend time with may be unseen or unnoticed by surrounding adults.
A common Euro-western notion is that unseen companions are not real; hence they are generally referred to in the literature as being imaginary.  In an extensive literature review, this thesis explores whether companionship with the unseen are one of many possible forms of relationships.  Dominant Euro-western claims that such relationships are imaginary are considered critically before the analysis widens in theoretical scope to draw on various alternative cultural accounts.  The analysis draws on the theoretical work of Jacques Derrida, Michel Foucault and Karen Barad, in particular.  An additional exploration considers the author’s own situated experiences of parenting a child who during her childhood years had companions that were unseen to the author.  The final analysis, based on a small selection of carefully chosen autoethnographic accounts, draws on the significance of ancestral inheritance. Within this specific research context that inheritance comprises my daughter’s Māori ancestry and our shared Celtic ancestry. 
Ancestral inheritance provides reflexive companionship for the entire thesis.  Examining inheritance sheds light on ways that traditional Euro-western claims of the imagined worlds of children, and consequently childhood, have produced a legacy of ideas which have subsequently held the term imaginary in place.  These dominant worldviews are shown to fall short in their capacity to cover the diversity of lived realities of children and their unseen (to others) companion(s).  Inheritance also denotes the culturally mediated birthright that may travel alongside a young child and how this birthright may provide insight and alternative cultural knowledge and understandings of various multiform relationship companions.
As a result of analysing several possible perspectives on the relationships under study, this thesis proposes the new term culturally compatible travelling companions (CCTC): companions who travel alongside children as ordinary, expected features of their lifespan.  This shift in term acknowledges that diverse notions of companionship, and the forms this may take, are integral and salient constructions of each culture’s historical and narrative accounts.  
This is timely research, as currently nearly 64% of young children aged between birth and four years of age attend some type of Early Childhood Education (ECE) service in Aotearoa New Zealand (Ministry of Education [MoE], 2019).  The national ECE curriculum document Te Whāriki (MoE, 2017) recognises the significance of young children’s relationships and understands those relationships within the rich and complex cultural knowledge patterning that travels alongside a young child.  
The aim of this research is to add to the theoretical understandings of the forms, functions and features of the multiple, complex relationship companions who may share the lives of young children, whether or not these companions are seen or discernible to those around the children.  It suggests an alternative perspective to the dominant view and offers provocations for those who work alongside young children to think differently about whether these relationship companions are indeed only imaginary.

year: 2020