Urban forest restoration

Definition

Urban forest (ngāhere) restoration is the intentional establishment and enhancement of native forest ecosystems within urban environments to restore biodiversity, ecological function, and long-term canopy cover.

What this strategy does

Creates multi-layered native forest structure through staged planting, soil remediation, and long-term management. Avoids short-term amenity planting that does not support forest succession.

Context

Urban environments in Aotearoa New Zealand are characterised by highly modified soils, fragmented habitats, and elevated weed and pest pressure, which constrain natural forest regeneration and require deliberate, long-term restoration approaches.¹

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Technical considerations

Design considerations

Long-term restoration planning

• Prepare a staged, adaptive restoration plan (10–20 years) defining vision, successional phases, management actions, and monitoring requirements.
• Address barriers to natural regeneration before planting.¹

Planting density and configuration

• Use dense planting (approximately 1 plant per 0.75 m) combined with soil ripping to rapidly form a canopy, suppress woody weeds, and create favourable forest microclimates.²
• Randomised and clustered planting patterns are preferred over linear layouts.¹

Reference ecosystems and species selection

• Use local urban forest remnants as reference systems to identify species tolerant of urban conditions.³
• Prioritise fast-establishing canopy species, followed by enrichment planting of late-successional species (typical of mature ecosystems) where natural recruitment (self-establishment from seed) is limited.³⁻⁴

Weed management integration

• Remove woody weed propagule sources (seed-producing invasive trees and shrubs) within approximately 100 m of the site and plan for ongoing weed control to protect planting investment.⁵

Implementation considerations

Design priority

• Sequence soil preparation, weed control, dense planting, and long-term maintenance as a single integrated system.

Key constraint

• Urban soils commonly exhibit compaction, ponding risk, and heterogeneous fertility, affecting growth rates and canopy development.²

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Issues & barriers

Weed reinvasion risk

• Urban seed rain (incoming seeds from surrounding areas) and soil seed banks (stored seeds in the soil) often favour exotic species, particularly along edges and following canopy disturbance, requiring sustained control to prevent canopy takeover.²˒⁶

Soil compaction

• Compacted soils reduce growth and canopy spread; the benefits of ripping are reduced under very wet conditions.²

Patch isolation

• Distance from native vegetation sources slows natural seed dispersal by wind and birds, increasing reliance on enrichment planting.²

Governance and delivery complexity

• Multiple objectives, landowners, and stakeholders, combined with limited funding and technical capacity, constrain implementation and long-term maintenance.⁷

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Synergies & opportunities

• Climate change – Urban forests intercept rainfall, improve infiltration, reduce runoff, contribute to urban cooling, and sequester and store carbon.⁸
• Human wellbeing – Biodiverse green spaces support physical health, mental wellbeing, cultural identity, and community cohesion.⁹⁻¹¹
• Disaster risk reduction – Increased canopy cover and soil permeability reduce flood risk.⁸

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Financial case

Value type

• Reduced stormwater infrastructure demand, improved air quality, and moderated urban temperatures through high-canopy native vegetation.⁸

Cost-effectiveness: Investment logic

• Biodiverse urban forests provide more resilient and durable ecosystem services than low-diversity plantings, reducing long-term maintenance and replacement costs.⁸

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Monitoring & evaluation metrics

Core metric

• Forest structure and composition can be assessed using the RECCE method, recording species by height tiers, cover, and site condition.¹²

Advanced or long-term metric

• Native species richness and diversity indices for plants and birds.¹³˒¹⁴
• Proportion of native versus non-native species
• Wildlife use (birds, invertebrates, bats) associated with restored forest patches.¹⁵˒¹⁶
• Ecosystem service performance (cooling, air quality, carbon storage).¹⁷⁻¹⁹

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Additional resources or tools

• National guides for planting native trees. Practical guidance for large-scale native planting programmes.
• Native to the West. Species selection and restoration guidance for western North Island contexts.
• RECCE Field Manual. Standardised forest assessment and monitoring method.

References

1. De Silva, K. (2019). Temporal development and regeneration dynamics of restored urban forests. MSc thesis, Victoria University of Wellington.
2. Sullivan, J. J., Meurk, C., Whaley, K. J., & Simcock, R. (2009). Restoring native ecosystems in urban Auckland: urban soils, isolation, and weeds as impediments to forest establishment. New Zealand Journal of Ecology, 33, 60–71.
3. Wallace, K. J., & Clarkson, B. D. (2019). Urban forest restoration ecology: a review from Hamilton, New Zealand. Journal of the Royal Society of New Zealand, 49(3), 347–369.
4. Wall, K., & Clarkson, B. D. (2006). Gully restoration guide: A guide to assist in the ecological restoration of Hamilton’s gully system. Hamilton City Council.
5. Sullivan, J. J., Timmins, S. M., & Williams, P. A. (2005). Movement of exotic plants into coastal native forests from gardens in northern New Zealand. New Zealand Journal of Ecology, 29, 1–10.
6. Overdyck, E., & Clarkson, B. D. (2012). Seed rain and soil seed banks limit native regeneration within urban forest restoration plantings in Hamilton City, New Zealand. New Zealand Journal of Ecology, 36, 177–190.
7. Busbridge, S., Clarkson, B. D., & Wallace, K. J. (2021). A tenuous link: Information transfer between urban ecological research and restoration practice. Urban Forestry & Urban Greening, 60, 127019.
8. Pataki, D., Alberti, M., Cadenasso, M., et al. (2021). The benefits and limits of urban tree planting for environmental and human health. Frontiers in Ecology and Evolution, 9, 603757.
9. Houlden, V., Jani, A., & Hong, A. (2021). Is biodiversity of greenspace important for human health and wellbeing? Urban Forestry & Urban Greening, 66, 127385.
10. Robinson, J. M., Breed, A. C., Camargo, A., Redvers, N., & Breed, M. F. (2024). Biodiversity and human health: A scoping review. Environmental Research, 246, 118115.
11. Meurk, C., Blaschke, P., & Simcock, R. (2013). Ecosystem services in New Zealand cities. In Ecosystem Services in New Zealand: Conditions and Trends (pp. 254–273).
12. Hurst, J. M., Allen, R. B., Coomes, D. A., & Duncan, R. P. (2011). Size-specific tree mortality varies with neighbourhood crowding and disturbance in a montane Nothofagus forest. PLoS ONE, 6(10), e26670.
13. Daly, A. J., Baetens, J. M., & De Baets, B. (2018). Ecological diversity: measuring the unmeasurable. Mathematics, 6(7), 119.
14. Roswell, M., Dushoff, J., & Winfree, R. (2021). A conceptual guide to measuring species diversity. Oikos, 130(3), 321–338.
15. Elliott Noe, E., Innes, J., Barnes, A. D., et al. (2022). Habitat provision is a major driver of native bird communities in restored urban forests. Journal of Animal Ecology, 91(7), 1444–1457.
16. Wood, E. M., & Esaian, S. (2020). The importance of street trees to urban avifauna. Ecological Applications, 30(7), e02149.
17. Sun, R., Xie, W., & Chen, L. (2024). Assessing the cooling benefits of blue-green space in urban parks. Urban Forestry & Urban Greening, 92, 128196.
18. Shah, S. I. A., Longley, P. A., & Singleton, A. D. (2022). Estimating local air quality using city-wide satellite imagery. Environmental Research Communications, 4(9), 095001.
19. Rendon, P., Erhard, M., & Nabel, J. E. M. S. (2024). Urban forest structure and composition strongly influence aboveground carbon storage. Urban Forestry & Urban Greening, 91, 128162.