title: Improving adaptive bagging methods for evolving data streams

authors: Bifet, Albert

subjects: computer science

abstract: We propose two new improvements for bagging methods on evolving data streams. Recently, two new variants of Bagging were proposed: ADWIN Bagging and Adaptive-Size Hoeffding Tree (ASHT) Bagging. ASHT Bagging uses trees of different sizes, and ADWIN Bagging uses ADWIN as a change detector to decide when to discard underperforming ensemble members. We improve ADWIN Bagging using Hoeffding Adaptive Trees, trees that can adaptively learn from data streams that change over time. To speed up the time for adapting to change of Adaptive-Size Hoeffding Tree (ASHT) Bagging, we add an error change detector for each classifier. We test our improvements by performing an evaluation study on synthetic and real-world datasets comprising up to ten million examples.

text: Improving adaptive bagging methods for evolving data streams We propose two new improvements for bagging methods on evolving data streams. Recently, two new variants of Bagging were proposed: ADWIN Bagging and Adaptive-Size Hoeffding Tree (ASHT) Bagging. ASHT Bagging uses trees of different sizes, and ADWIN Bagging uses ADWIN as a change detector to decide when to discard underperforming ensemble members. We improve ADWIN Bagging using Hoeffding Adaptive Trees, trees that can adaptively learn from data streams that change over time. To speed up the time for adapting to change of Adaptive-Size Hoeffding Tree (ASHT) Bagging, we add an error change detector for each classifier. We test our improvements by performing an evaluation study on synthetic and real-world datasets comprising up to ten million examples.

year: 2009

title: Composition, structure and restoration potential of riparian forest remnants, Hawke's Bay, New Zealand

authors: West, Moari

subjects: community structure

abstract: Extensive modification of riparian zones across the globe has seen a reduction in the important functions and services provided by the vegetation. Maintaining water quality, sediment control, nutrient cycling, habitat provision, climate change mitigation, and increased biodiversity value are a few of the services provided by riparian vegetation. Within New Zealand, approximately 16,000 ha of native forest has been cleared in recent times. This forest loss, compounded by historical forest loss over the previous seven centuries (14 million ha as of 2002), alongside the important services, gives native forests occurring within riparian zones increased value. This research assessed the species composition, community structure, restoration potential, and restoration needs of native riparian forest remnants in the Hawke’s Bay Region of New Zealand. 
Eleven riparian forest remnants that were predominately comprised of native species and were greater than 0.25 ha in size were selected to be surveyed. Empirical data was collected through vegetation surveys, including 10 x 10 m RECCE plots, forest health assessments, bird counts, and visual soils assessments. Bagged regression trees were utilized to determine which explanatory variables were the most important for the species composition and community structure of the sites surveyed. Variable importance plots and partial dependence plots were used to interpret the results from the bagged regression trees. 
Of the 127 vascular plant species identified, 66 were native or endemic and 61 were exotic. Only one species, Kunzea robusta, was deemed threatened. Species found in the greatest number of plots included, Melicytus ramiflorus, Coprosma robusta, K. robusta, and Salix fragilis. Bagged regression tree models indicated that the six key explanatory variables for the community structure and species composition of the sites surveyed were annual rainfall, elevation, mesotopographic index, road density, slope, and distance from the river. Partial dependence plots indicated that sites with high native species richness and importance, low exotic species richness and importance, high understory density and canopy cover were those with an annual rainfall between 1050 mm and 1200 mm, an elevation above 150 m above sea level (a.s.l.), a mesotopographic index of 45 or above, a road density of 0.60 km² or below, a slope between 15° and 30°. 
Desirable or good species composition and community structure was associated with high native species richness and importance, low exotic species richness and importance, a high understory density, and a high canopy cover. Moderate forest health, good soil quality, and a mixture of good and poor community structure and species composition was observed across the Ngaruroro, Tutaekuri, and Tukituki Rivers. Sites or portions of a site with an annual rainfall outside of the 1050 mm to 1200 mm desirable range, that are present further than 190 m from the river’s edge, have an elevation less than 150 m a.s.l., have a mesotopographic index of greater than 45, a road density of 0.60 km² or below, and have a slope outside of the 15° to 30° range, may require more intensive restoration efforts and greater investments. 
Overall, sites with good current community structure and species composition were deemed to have the highest restoration potential as such sites had fewer restoration needs and would require fewer interventions and lower investments. Two of the Tukituki River sites, named TT-4 and TT-5, had the highest restoration potential of all the sites surveyed. This was largely due to the presence of diagnostic species from the ecological reference used, and the close proximity to each other and to a managed forest remnant. Sites TT-4 and TT-5 could be made a priority for restoration projects utilising more passive methods. The remaining Tukituki River site named MK-3  and one of the Ngaruroro River sites NG-6 were deemed to have the lowest restoration potential, particularly due to the lack of seed sources and poor community structure and species composition. Sites MK-3 and NG-6 could be made a priority in restoration projects utilising more active methods. 
Future restoration projects should aim to improve species composition and community structure. The improvements could be made by removing undesirable species such as exotic and weed species and introduce desirable native and site-appropriate species. Interventions could utilize canopy manipulation, nurse plants, and ecological references.
This research contributes to the national reporting of quantitative data describing the community structure and species composition of native riparian forests in New Zealand, provides a quantitative model of the most important explanatory variables for community structure and species composition in the riparian forests surveyed, and contributes to the understanding of the restoration potential of riparian forest remnants in the region. Future studies could further explore the suitability of the restoration methods and ecological references outlined in this research, the future risk of forest clearance.
   1 MK stands for the Makaretu River which feeds into the Tukituki River.

text: Composition, structure and restoration potential of riparian forest remnants, Hawke's Bay, New Zealand Extensive modification of riparian zones across the globe has seen a reduction in the important functions and services provided by the vegetation. Maintaining water quality, sediment control, nutrient cycling, habitat provision, climate change mitigation, and increased biodiversity value are a few of the services provided by riparian vegetation. Within New Zealand, approximately 16,000 ha of native forest has been cleared in recent times. This forest loss, compounded by historical forest loss over the previous seven centuries (14 million ha as of 2002), alongside the important services, gives native forests occurring within riparian zones increased value. This research assessed the species composition, community structure, restoration potential, and restoration needs of native riparian forest remnants in the Hawke’s Bay Region of New Zealand. 
Eleven riparian forest remnants that were predominately comprised of native species and were greater than 0.25 ha in size were selected to be surveyed. Empirical data was collected through vegetation surveys, including 10 x 10 m RECCE plots, forest health assessments, bird counts, and visual soils assessments. Bagged regression trees were utilized to determine which explanatory variables were the most important for the species composition and community structure of the sites surveyed. Variable importance plots and partial dependence plots were used to interpret the results from the bagged regression trees. 
Of the 127 vascular plant species identified, 66 were native or endemic and 61 were exotic. Only one species, Kunzea robusta, was deemed threatened. Species found in the greatest number of plots included, Melicytus ramiflorus, Coprosma robusta, K. robusta, and Salix fragilis. Bagged regression tree models indicated that the six key explanatory variables for the community structure and species composition of the sites surveyed were annual rainfall, elevation, mesotopographic index, road density, slope, and distance from the river. Partial dependence plots indicated that sites with high native species richness and importance, low exotic species richness and importance, high understory density and canopy cover were those with an annual rainfall between 1050 mm and 1200 mm, an elevation above 150 m above sea level (a.s.l.), a mesotopographic index of 45 or above, a road density of 0.60 km² or below, a slope between 15° and 30°. 
Desirable or good species composition and community structure was associated with high native species richness and importance, low exotic species richness and importance, a high understory density, and a high canopy cover. Moderate forest health, good soil quality, and a mixture of good and poor community structure and species composition was observed across the Ngaruroro, Tutaekuri, and Tukituki Rivers. Sites or portions of a site with an annual rainfall outside of the 1050 mm to 1200 mm desirable range, that are present further than 190 m from the river’s edge, have an elevation less than 150 m a.s.l., have a mesotopographic index of greater than 45, a road density of 0.60 km² or below, and have a slope outside of the 15° to 30° range, may require more intensive restoration efforts and greater investments. 
Overall, sites with good current community structure and species composition were deemed to have the highest restoration potential as such sites had fewer restoration needs and would require fewer interventions and lower investments. Two of the Tukituki River sites, named TT-4 and TT-5, had the highest restoration potential of all the sites surveyed. This was largely due to the presence of diagnostic species from the ecological reference used, and the close proximity to each other and to a managed forest remnant. Sites TT-4 and TT-5 could be made a priority for restoration projects utilising more passive methods. The remaining Tukituki River site named MK-3  and one of the Ngaruroro River sites NG-6 were deemed to have the lowest restoration potential, particularly due to the lack of seed sources and poor community structure and species composition. Sites MK-3 and NG-6 could be made a priority in restoration projects utilising more active methods. 
Future restoration projects should aim to improve species composition and community structure. The improvements could be made by removing undesirable species such as exotic and weed species and introduce desirable native and site-appropriate species. Interventions could utilize canopy manipulation, nurse plants, and ecological references.
This research contributes to the national reporting of quantitative data describing the community structure and species composition of native riparian forests in New Zealand, provides a quantitative model of the most important explanatory variables for community structure and species composition in the riparian forests surveyed, and contributes to the understanding of the restoration potential of riparian forest remnants in the region. Future studies could further explore the suitability of the restoration methods and ecological references outlined in this research, the future risk of forest clearance.
   1 MK stands for the Makaretu River which feeds into the Tukituki River.

year: 2021

title: Diacritic Restoration and the Development of a Part-of-Speech Tagset for the Māori Language

authors: Cocks, John

subjects: Māori

abstract: This thesis investigates two fundamental problems in natural language processing: diacritic restoration and part-of-speech tagging. Over the past three decades, statistical approaches to diacritic restoration and part-of-speech tagging have grown in interest as a consequence of the increasing availability of manually annotated training data in major languages such as English and French. However, these approaches are not practical for most minority languages, where appropriate training data is either non-existent or not publically available. Furthermore, before developing a part-of-speech tagging system, a suitable tagset is required for that language. In this thesis, we make the following contributions to bridge this gap:

Firstly, we propose a method for diacritic restoration based on naive Bayes classifiers that act at word-level. Classifications are based on a rich set of features, extracted automatically from training data in the form of diacritically marked text. This method requires no additional resources, which makes it language independent. The algorithm was evaluated on one language, namely Māori, and an accuracy exceeding 99% was observed.

Secondly, we present our work on creating one of the necessary resources for the development of a part-of-speech tagging system in Māori, that of a suitable tagset. The tagset described was developed in accordance with the EAGLES guidelines for morphosyntactic annotation of corpora, and was the result of in-depth analysis of the Māori grammar.

text: Diacritic Restoration and the Development of a Part-of-Speech Tagset for the Māori Language This thesis investigates two fundamental problems in natural language processing: diacritic restoration and part-of-speech tagging. Over the past three decades, statistical approaches to diacritic restoration and part-of-speech tagging have grown in interest as a consequence of the increasing availability of manually annotated training data in major languages such as English and French. However, these approaches are not practical for most minority languages, where appropriate training data is either non-existent or not publically available. Furthermore, before developing a part-of-speech tagging system, a suitable tagset is required for that language. In this thesis, we make the following contributions to bridge this gap:

Firstly, we propose a method for diacritic restoration based on naive Bayes classifiers that act at word-level. Classifications are based on a rich set of features, extracted automatically from training data in the form of diacritically marked text. This method requires no additional resources, which makes it language independent. The algorithm was evaluated on one language, namely Māori, and an accuracy exceeding 99% was observed.

Secondly, we present our work on creating one of the necessary resources for the development of a part-of-speech tagging system in Māori, that of a suitable tagset. The tagset described was developed in accordance with the EAGLES guidelines for morphosyntactic annotation of corpora, and was the result of in-depth analysis of the Māori grammar.

year: 2012