title: Variability of blue carbon stocks in restored saltmarsh wetlands: Bay of Plenty, Aotearoa New Zealand

authors: Visser, Jade Skye

abstract: As anthropogenic pressures including urbanisation and climate change continue to pressure the natural environment, there is a great need to focus on solutions that both increase ecosystem resilience and mitigate climate change. Coastal wetlands are a “powerhouse” environment that have the potential to achieve this and much more. Among the variety of coastal wetlands, saltmarsh habitats are one of the most degraded environments globally, with a mere <10% estimated to remain in Aotearoa New Zealand. Many saltmarshes have been lost  due to factors such as,  conversion to pasture, and/or environmental degradation. As part of the conversation around saltmarsh restoration, nature-based solutions are a tool that is being increasingly considered when it comes to climate change mitigation and adaptation,  due to the large potential saltmarshes possess to sequester CO2 alongside adapting to sea level rise such as by providing a space for flood water and for vegetation to slow down storm surges, alongside other environmental and societal benefits.

This study investigates the blue carbon dynamics in restored and control saltmarsh habitats in the Bay of Plenty Aotearoa New Zealand, focusing on bulk density, concentration of carbon (%), Total Organic Carbon (TOC), Sediment Accumulation Rates (SAR), and Carbon Accumulation Rates (CAR). We focus on changes in blue carbon with time since saltmarsh restoration. Bulk density analysis revealed minimal variability among sites, with Matua Saltmarsh exhibiting the largest standard error (0.765 ± 0.057g cm3) and Wainui River Saltmarsh the lowest mean bulk density (0.633 ± 0.032g cm3). Carbon concentration was generally highly variable across sites, with Matua Saltmarsh exhibiting the highest mean concentration (5.83 ± 1.151%) and Wainui Repo Whenua the lowest (2.91 ± 0.26%). Total organic carbon stock decreased with depth across sites, with Matua Saltmarsh having the highest total organic carbon stock (1.21 ± 0.005g cm3 or 121.42 ± 0.534t ha-1) and Te Awa o Ngātoroirangi the lowest (0.69 ± 0.004g cm3 or 68.66 ± 0.401t ha-1). Carbon accumulation rates generally increased with restoration age, with Wainui River Saltmarsh exhibiting the highest sediment accumulation rate (11.57mm yr-1) and Matua Saltmarsh the highest carbon accumulation rate (161.87g m-2 yr-1 over the last 20 years). While no distinct trends in blue carbon stocks and concentration emerged between the restored and control environments, it is notable that restored saltmarshes consistently exhibited substantial carbon stocks compared to controls and global standards. Moreover, there were higher mean TOC figures within the first ~30 years post-restoration. These results align with expectations from previous studies, emphasizing the efficacy of saltmarsh restoration efforts in enhancing future carbon storage potential in Aotearoa. 

These findings underscore the need for comprehensive investigations into the roles of vegetation, sedimentation rates, microbial processes, alongside catchment hydrological conditions history. This thesis also highlights that long-term monitoring beyond the initial 20- 30 years post-restoration is crucial to comprehensively understand the trajectory of blue carbon dynamics. In addition, comparative studies accounting for diverse restoration techniques and assessments of broader ecosystem services delivered by saltmarsh restoration are essential. Addressing these factors will deepen our understanding of the specific mechanisms influencing blue carbon dynamics in Aotearoa's restored saltmarshes.

text: Variability of blue carbon stocks in restored saltmarsh wetlands: Bay of Plenty, Aotearoa New Zealand As anthropogenic pressures including urbanisation and climate change continue to pressure the natural environment, there is a great need to focus on solutions that both increase ecosystem resilience and mitigate climate change. Coastal wetlands are a “powerhouse” environment that have the potential to achieve this and much more. Among the variety of coastal wetlands, saltmarsh habitats are one of the most degraded environments globally, with a mere <10% estimated to remain in Aotearoa New Zealand. Many saltmarshes have been lost  due to factors such as,  conversion to pasture, and/or environmental degradation. As part of the conversation around saltmarsh restoration, nature-based solutions are a tool that is being increasingly considered when it comes to climate change mitigation and adaptation,  due to the large potential saltmarshes possess to sequester CO2 alongside adapting to sea level rise such as by providing a space for flood water and for vegetation to slow down storm surges, alongside other environmental and societal benefits.

This study investigates the blue carbon dynamics in restored and control saltmarsh habitats in the Bay of Plenty Aotearoa New Zealand, focusing on bulk density, concentration of carbon (%), Total Organic Carbon (TOC), Sediment Accumulation Rates (SAR), and Carbon Accumulation Rates (CAR). We focus on changes in blue carbon with time since saltmarsh restoration. Bulk density analysis revealed minimal variability among sites, with Matua Saltmarsh exhibiting the largest standard error (0.765 ± 0.057g cm3) and Wainui River Saltmarsh the lowest mean bulk density (0.633 ± 0.032g cm3). Carbon concentration was generally highly variable across sites, with Matua Saltmarsh exhibiting the highest mean concentration (5.83 ± 1.151%) and Wainui Repo Whenua the lowest (2.91 ± 0.26%). Total organic carbon stock decreased with depth across sites, with Matua Saltmarsh having the highest total organic carbon stock (1.21 ± 0.005g cm3 or 121.42 ± 0.534t ha-1) and Te Awa o Ngātoroirangi the lowest (0.69 ± 0.004g cm3 or 68.66 ± 0.401t ha-1). Carbon accumulation rates generally increased with restoration age, with Wainui River Saltmarsh exhibiting the highest sediment accumulation rate (11.57mm yr-1) and Matua Saltmarsh the highest carbon accumulation rate (161.87g m-2 yr-1 over the last 20 years). While no distinct trends in blue carbon stocks and concentration emerged between the restored and control environments, it is notable that restored saltmarshes consistently exhibited substantial carbon stocks compared to controls and global standards. Moreover, there were higher mean TOC figures within the first ~30 years post-restoration. These results align with expectations from previous studies, emphasizing the efficacy of saltmarsh restoration efforts in enhancing future carbon storage potential in Aotearoa. 

These findings underscore the need for comprehensive investigations into the roles of vegetation, sedimentation rates, microbial processes, alongside catchment hydrological conditions history. This thesis also highlights that long-term monitoring beyond the initial 20- 30 years post-restoration is crucial to comprehensively understand the trajectory of blue carbon dynamics. In addition, comparative studies accounting for diverse restoration techniques and assessments of broader ecosystem services delivered by saltmarsh restoration are essential. Addressing these factors will deepen our understanding of the specific mechanisms influencing blue carbon dynamics in Aotearoa's restored saltmarshes.

year: 2023-12-24

title: What explains the wealth gap between immigrants and the New Zealand born?

authors: Gibson, John

subjects: immigration

abstract: Immigrants are typically found to have less wealth and hold it in different forms than the native born. These differences may affect both the economic assimilation of immigrants and overall portfolio allocation when immigrants are a large share of the population, as in New Zealand. In this paper, data from the 2001 Household Savings Survey are used to examine wealth differences between immigrants and the New Zealand-born. Differences in the allocation of portfolios between housing and other forms of wealth are described. Unconditional and conditional wealth quantiles are examined using parametric models. Semi-parametric methods are used to decompose differences in net worth at different parts of the wealth distribution into the part due to differences in characteristics and the part due to differences in the returns to characteristics.

text: What explains the wealth gap between immigrants and the New Zealand born? Immigrants are typically found to have less wealth and hold it in different forms than the native born. These differences may affect both the economic assimilation of immigrants and overall portfolio allocation when immigrants are a large share of the population, as in New Zealand. In this paper, data from the 2001 Household Savings Survey are used to examine wealth differences between immigrants and the New Zealand-born. Differences in the allocation of portfolios between housing and other forms of wealth are described. Unconditional and conditional wealth quantiles are examined using parametric models. Semi-parametric methods are used to decompose differences in net worth at different parts of the wealth distribution into the part due to differences in characteristics and the part due to differences in the returns to characteristics.

year: 2007-09

title: Harakeke (Phormium tenax) ecology and historical management by Maori: The changing landscape in New Zealand

authors: Wehi, Priscilla M.

subjects: ethnobotany

abstract: Harakeke (Phormium tenax: Phormiaceae) is an important weaving resource for the indigenous Maori people of New Zealand. This research project investigates Maori knowledge of harakeke ecology and management practices prior to the early 20th century within the context of a study of relevant environmental parameters that limit its natural distribution. Ecological information referring to harakeke was analysed from interviews with elders and ancestral sayings (whakatauki). As well, documents from the late 181h to the early 20th century were examined, and environmental parameters for both harakeke and wharariki (Phormium cookianum) were quantified and analysed using correlative models. 
Interviews with 11 elders (from Waikato and Northland) identified key issues in harakeke management, including 'correct' harvesting procedures, use of natural harakeke stands, and specific use of different varieties. Planting practices varied regionally. Three different methods of excess harakeke disposal were reported, including burning. The 15 whakatauki analysed emphasise the interconnectedness of ecosystems, including pollinator-plant relationships for kaka and bellbirds. Four whakataukirefer to environmental tolerances for harakeke and two to the use of fire to stimulate harakeke growth. Others refer to competition between shoots, nutrient requirements, and the growth and multiplication of harakeke offsets. 
Numerous early reports indicate that harakeke has been cultivated throughout much of New Zealand, with cultivations ranging in size from a few bushes to at least several acres. Thirty six varieties were linked to specific weaving uses. Twenty varieties were cultivated, but ten prized fibre varieties were also harvested from natural stands. Numbers of recorded varieties varied between districts, with 31 recorded in Taranaki but only two recorded by name for Northland. Valued varieties, including raumoa and oue, were dispersed throughout the North Island. Mapping different varieties revealed a wide spatial spread for varieties such as rataroa and oue. Specific management techniques included seed germination as well as vegetative propagation. Early records of harakeke pests were not found. Records of harakeke irrigation and the use of fire indicate that Maori created suitable conditions for new cultivations or pii harakeke, which may also have prevented insect infestation. Cumulatively, there is evidence of extensive active management of harakeke. Wharariki and harakeke were found to have distinct environmental niches, with wharariki better able to withstand cooler temperatures, higher rainfall and greater frequency of ground frost than harakeke.
Predictive mapping of harakeke for the northern region of New Zealand shows a low probability of naturally occurring harakeke in much of the Northland and Waikato interior, and a high probability in coastal areas with warm temperatures. It seems likely that Maori transported harakeke into areas where it was unlikely to have occurred naturally and that some apparently 'natural' stands ofharakeke were created and maintained by Maori.
Maori cultivation, dispersal and active management of harakeke, as well as possible creation of wetland areas, emphasises the importance of harakeke as an economic resource prior to European colonisation, and indicates how the New Zealand landscape may have been transformed. Maori ecological knowledge can contribute new perspectives to restoration ecology and ecosystem research.

text: Harakeke (Phormium tenax) ecology and historical management by Maori: The changing landscape in New Zealand Harakeke (Phormium tenax: Phormiaceae) is an important weaving resource for the indigenous Maori people of New Zealand. This research project investigates Maori knowledge of harakeke ecology and management practices prior to the early 20th century within the context of a study of relevant environmental parameters that limit its natural distribution. Ecological information referring to harakeke was analysed from interviews with elders and ancestral sayings (whakatauki). As well, documents from the late 181h to the early 20th century were examined, and environmental parameters for both harakeke and wharariki (Phormium cookianum) were quantified and analysed using correlative models. 
Interviews with 11 elders (from Waikato and Northland) identified key issues in harakeke management, including 'correct' harvesting procedures, use of natural harakeke stands, and specific use of different varieties. Planting practices varied regionally. Three different methods of excess harakeke disposal were reported, including burning. The 15 whakatauki analysed emphasise the interconnectedness of ecosystems, including pollinator-plant relationships for kaka and bellbirds. Four whakataukirefer to environmental tolerances for harakeke and two to the use of fire to stimulate harakeke growth. Others refer to competition between shoots, nutrient requirements, and the growth and multiplication of harakeke offsets. 
Numerous early reports indicate that harakeke has been cultivated throughout much of New Zealand, with cultivations ranging in size from a few bushes to at least several acres. Thirty six varieties were linked to specific weaving uses. Twenty varieties were cultivated, but ten prized fibre varieties were also harvested from natural stands. Numbers of recorded varieties varied between districts, with 31 recorded in Taranaki but only two recorded by name for Northland. Valued varieties, including raumoa and oue, were dispersed throughout the North Island. Mapping different varieties revealed a wide spatial spread for varieties such as rataroa and oue. Specific management techniques included seed germination as well as vegetative propagation. Early records of harakeke pests were not found. Records of harakeke irrigation and the use of fire indicate that Maori created suitable conditions for new cultivations or pii harakeke, which may also have prevented insect infestation. Cumulatively, there is evidence of extensive active management of harakeke. Wharariki and harakeke were found to have distinct environmental niches, with wharariki better able to withstand cooler temperatures, higher rainfall and greater frequency of ground frost than harakeke.
Predictive mapping of harakeke for the northern region of New Zealand shows a low probability of naturally occurring harakeke in much of the Northland and Waikato interior, and a high probability in coastal areas with warm temperatures. It seems likely that Maori transported harakeke into areas where it was unlikely to have occurred naturally and that some apparently 'natural' stands ofharakeke were created and maintained by Maori.
Maori cultivation, dispersal and active management of harakeke, as well as possible creation of wetland areas, emphasises the importance of harakeke as an economic resource prior to European colonisation, and indicates how the New Zealand landscape may have been transformed. Maori ecological knowledge can contribute new perspectives to restoration ecology and ecosystem research.

year: 2005