Urban ecological restoration faces distinct challenges due to the highly modified biophysical con... more Urban ecological restoration faces distinct challenges due to the highly modified biophysical conditions that characterise cities. To overcome these difficulties and assist in decision- making, ecological principles should underpin comprehensive analyses at both the landscape and site-specific scale. With increasing recognition of the role that the environment plays in social and economic prosperity, there are a growing number of strategies focused on increasing native habitat in urban centres. This thesis presents three integrated studies in support of Hamilton City Council’s goal under the Nature in the City Strategy to increase indigenous vegetation cover from about 1.8% to a minimum of 10% by 2050. Landform and ecological unit representativeness analyses in the city reveal the extent of under-represented environments, but it also presents opportunities to improve this criterion rapidly. Then, a multicriteria ecological prioritisation tool specifically developed for Hamilton City identified the most ecologically intact sites that could support the selection of potential gully and reserve restoration sites following the Nature in the City Strategy. Finally, at the site-specific scale, assessments of the vegetation composition and structure of three kahikatea forest remnants determined appropriate restoration strategies that may guide restoration projects in other cities.
Landform and ecological unit areas in Hamilton City that would need to be restored to meet ecological representativeness thresholds under the 10% goal are presented. The peatlands, alluvial plains and hills landform and their respective ecological units are severely under- represented, while the gullies are sufficiently represented. However, gullies tend to contain more micro-environments and diversity than the other landforms, so restoring them may provide greater biodiversity rewards. Compared to previous representativeness studies of Hamilton City, this assessment provides more refined information available on a geographic information system (GIS) and highlights opportunities for its rapid improvement. For example, adequately representing some of the most under-represented ecological units, such as peat domes, would require the least restoration effort by extent (14 hectares (ha)). While improving representativeness could enhance the city’s pool of indigenous species, this study demonstrated that it should not be used alone to prioritise restoration sites in highly modified urban environments. Rather, representativeness could be included in a wider range of criteria and more appropriately employed for regional or national strategies.
About 198 ha of Hamilton City is dominated by native vegetation, requiring the restoration of 886 ha or approximately 32 ha annually from 2023 to achieve the 10% goal by 2050. A prioritisation tool specifically developed for the city comprising eight ecological criteria identified 873 gully and reserve sites with the most intact ecological integrity that satisfy this area. These sites were allocated into five prioritisation categories to support the adoption of a staged approach for this city-wide restoration project. Sites that received high ecological scores included sections within Hamilton Gardens, Hammond Park, Minogue Park, Kirikiriroa gully, the major riverside gully and Mangaonua gully. Most high-ranking sites were found in the city’s east, although restoring sites on both sides of Hamilton City would enhance ecological connectivity on a regional scale. As the city expands, restoring large undeveloped areas would likely require fewer resources than restoring many dispersed isolated patches. Similarly, restoring whole systems, such as the high-ranking Kirikiriroa gully, is suggested to provide greater biodiversity rewards. Further application of this tool could incorporate social, economic and cultural criteria for a more holistic prioritisation of sites.
The condition of kahikatea (Dacrycarpus dacrydioides, white pine) forest remnants at Totara Park, Hillcrest Park and Grove Park was examined and compared with Te Papanui (Claudelands Bush/Jubilee Park) as the reference site to identify restoration strategies. Age structure analyses found that Hillcrest Park comprises the oldest kahikatea population with an average age of 82 years, followed by Grove Park (70 years), Te Papanui (60 years) and Totara Park (32 years). The Kahikatea Green Wheel, life form and epiphyte analyses highlighted the importance of Totara Park’s high water table and sheltered conditions. While Te Papanui was found to support the most native vascular plants (64 species), Totara Park’s conditions have contributed to its greater species richness (41 species) than Hillcrest Park (15 species) and Grove Park (eight species). More native epiphytes were also identified at Totara Park (nine) than Te Papanui (six), Hillcrest Park (one) and Grove Park (none). Epiphytes absent from Te Papanui found at Totara Park may be due to the loss of the once abundant Dicksonia squarrosa (whekī), a prominent host. Differences between the native vascular plants found at Te Papanui and the case studies signal gaps in characteristic species of kahikatea forest that could be filled by relevant planting at each site. While Totara Park’s remnant requires a careful manipulation restoration strategy to gradually remove troublesome plants without disturbing its locally rare native flora, the ecological integrity of Hillcrest Park and Grove Park could improve most from buffer, ground cover and shrub tier plantings.
Tree ferns are ubiquitous in New Zealand forests, but there is limited knowledge of their role in... more Tree ferns are ubiquitous in New Zealand forests, but there is limited knowledge of their role in urban plant communities and potential use in restoration. We assessed sixteen sites by measuring 200 m 2 plots to investigate how tree ferns influence vascular plant composition in Hamilton, North Island, New Zealand. The sixteen plots were assigned to four site type combinations based on restoration status (restored or unrestored) and tree fern presence, each with four plots. Average native plant species richness was higher at sites with tree ferns (36 ± 16; S = 68) than at sites without (19 ± 14; S = 41), with more diverse ground fern and epiphyte assemblages. Higher native plant richness at restored sites (34 ± 18; S = 62) compared to unrestored sites (20 ± 14, S = 44) was partially attributed to increased plant abundances. Multivariate analyses revealed differences in plant community composition among our site types. Angiosperms and conifers were less prevalent in plots with tree ferns, suggesting competitive relationships among these groups. However, tree ferns were associated with some shade-tolerant trees, such as Schefflera digitata J.R.Forst. & G.Forst. Indicator species of sites with tree ferns were mainly ground ferns and epiphytes (e.g., Blechnum parrisiae Christenh. and Trichomanes venosum R.Br.), whereas species with high fidelity to sites without tree ferns were pioneer trees and shrubs (e.g., Pittosporum eugenioides A.Cunn.). Community structure analyses revealed that total basal areas were highest at unrestored sites with tree ferns, but restored sites exhibited more diverse tree communities. Environmental predictors that correlated significantly with the compositional differences among our site types were tree fern basal area and restoration age. Our results highlight the need to reconsider the potential of tree ferns in current restoration practice. Tree ferns were found to augment native plant diversity in our study, indicating their potential to enhance urban ecological restoration projects in New Zealand.
More than a thousand iNaturalist NZ observations were compiled and analysed to determine common v... more More than a thousand iNaturalist NZ observations were compiled and analysed to determine common vascular epiphyte-host relationships in Hamilton, North Island, New Zealand. Dicksonia squarrosa supported the most epiphytes, followed by Salix cinerea, Melicytus ramiflorus and Cyathea medullaris. Epiphytes displaying stronger host specificity, such as Tmesipteris elongata and Phlegmariurus varius, were often on D. squarrosa. In comparison, generalist epiphytes, including Pyrrosia eleagnifolia and Lecanopteris pustulata, were mainly on M. ramiflorus and S. cinerea. A detailed study of 60 D. squarrosa in a single gully investigated factors supporting the host quality of D. squarrosa. Dicksonia squarrosa diameter at breast height (DBH), height, caudex surface area, and distance to the stream and vegetation patch edge were measured. Dicksonia squarrosa that hosted epiphytes were significantly taller, further from the patch edge and had a larger surface area. Epiphyte species richness was higher on D. squarrosa further from the patch edge. The epiphyte communities examined are likely characteristic of highly modified urban ecosystems. Future research investigating the impact of host traits and microclimate on epiphyte-host networks is required to fully elucidate these relationships in urban environments.
Identifying appropriate restoration strategies is vital for successful urban remnant restora- tio... more Identifying appropriate restoration strategies is vital for successful urban remnant restora- tion, but projects often lack consistent methods that distinguish them. In New Zealand, there are unique opportunities to restore depleted Dacrycarpus dacrydioides (A.Rich.) de Laub. (kahikatea, white pine) semi-swamp forest remnants in numerous urban centres. To assess potential restoration strategies for three kahikatea remnants in Hamilton City, we compared their physical features, native vascular species composition, age structures, life forms and epiphytes with a notional reference site (Te Papanui). Numerous native vascular species gaps are revealed among Te Papanui (66 species), Totara Park (40 species), Hillcrest Park (15 species) and Grove Park (nine species). Age structure analyses suggest that Hillcrest Park comprises the oldest kahikatea population, with an average age of 82 years, followed by Grove Park (70 years), Te Papanui (60 years) and Totara Park (32 years). A native floristic analysis of thirteen life forms found that Te Papanui contains the most (11), followed by Totara Park (eight), Grove Park (six) and Hillcrest Park (five). Despite the abundance of invasive plants at Totara Park, its high-water table and favourable humid, sheltered conditions support more epiphytes (nine) than Te Papanui (six), Hillcrest Park (one; Pyrrosia eleagnifolia), and Grove Park (none). Epiphytes absent from Te Papanui found at Totara Park may be due to the loss of the once abundant tree fern and host, Dicksonia squarrosa (whekī). Totara Park requires careful manipulation of troublesome weeds, whereas Hillcrest Park and Grove Park necessitate buffer extensions and native understory plantings. This study provides a simple framework that uses biophysical differences among urban remnants and a reference site to reveal suitable restoration strategies that could guide other urban restoration projects regionally and nationally.
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Thesis by Hannah Rogers
Landform and ecological unit areas in Hamilton City that would need to be restored to meet ecological representativeness thresholds under the 10% goal are presented. The peatlands, alluvial plains and hills landform and their respective ecological units are severely under- represented, while the gullies are sufficiently represented. However, gullies tend to contain more micro-environments and diversity than the other landforms, so restoring them may provide greater biodiversity rewards. Compared to previous representativeness studies of Hamilton City, this assessment provides more refined information available on a geographic information system (GIS) and highlights opportunities for its rapid improvement. For example, adequately representing some of the most under-represented ecological units, such as peat domes, would require the least restoration effort by extent (14 hectares (ha)). While improving representativeness could enhance the city’s pool of indigenous species, this study demonstrated that it should not be used alone to prioritise restoration sites in highly modified urban environments. Rather, representativeness could be included in a wider range of criteria and more appropriately employed for regional or national strategies.
About 198 ha of Hamilton City is dominated by native vegetation, requiring the restoration of 886 ha or approximately 32 ha annually from 2023 to achieve the 10% goal by 2050. A prioritisation tool specifically developed for the city comprising eight ecological criteria identified 873 gully and reserve sites with the most intact ecological integrity that satisfy this area. These sites were allocated into five prioritisation categories to support the adoption of a staged approach for this city-wide restoration project. Sites that received high ecological scores included sections within Hamilton Gardens, Hammond Park, Minogue Park, Kirikiriroa gully, the major riverside gully and Mangaonua gully. Most high-ranking sites were found in the city’s east, although restoring sites on both sides of Hamilton City would enhance ecological connectivity on a regional scale. As the city expands, restoring large undeveloped areas would likely require fewer resources than restoring many dispersed isolated patches. Similarly, restoring whole systems, such as the high-ranking Kirikiriroa gully, is suggested to provide greater biodiversity rewards. Further application of this tool could incorporate social, economic and cultural criteria for a more holistic prioritisation of sites.
The condition of kahikatea (Dacrycarpus dacrydioides, white pine) forest remnants at Totara Park, Hillcrest Park and Grove Park was examined and compared with Te Papanui (Claudelands Bush/Jubilee Park) as the reference site to identify restoration strategies. Age structure analyses found that Hillcrest Park comprises the oldest kahikatea population with an average age of 82 years, followed by Grove Park (70 years), Te Papanui (60 years) and Totara Park (32 years). The Kahikatea Green Wheel, life form and epiphyte analyses highlighted the importance of Totara Park’s high water table and sheltered conditions. While Te Papanui was found to support the most native vascular plants (64 species), Totara Park’s conditions have contributed to its greater species richness (41 species) than Hillcrest Park (15 species) and Grove Park (eight species). More native epiphytes were also identified at Totara Park (nine) than Te Papanui (six), Hillcrest Park (one) and Grove Park (none). Epiphytes absent from Te Papanui found at Totara Park may be due to the loss of the once abundant Dicksonia squarrosa (whekī), a prominent host. Differences between the native vascular plants found at Te Papanui and the case studies signal gaps in characteristic species of kahikatea forest that could be filled by relevant planting at each site. While Totara Park’s remnant requires a careful manipulation restoration strategy to gradually remove troublesome plants without disturbing its locally rare native flora, the ecological integrity of Hillcrest Park and Grove Park could improve most from buffer, ground cover and shrub tier plantings.
Papers by Hannah Rogers