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Temporal Development and Regeneration Dynamics of Restored Urban Forests

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posted on 2021-12-08, 14:05 authored by De Silva, Katherine

Urban forest restoration programmes are a key tool used to initiate, re-create or accelerate the succession of forest species; improving ecosystem services, function, resilience and biodiversity. Succession is a temporal shift in species dominance driven by abiotic and biotic influences, but over decadal timescales the trajectory and success of restoration plantings in degraded urban environments can be hindered. To facilitate the successful reconstruction of forest ecosystems from scratch, an understanding of the temporal patterns in planted forest development, dynamics of seedling regeneration and dominant drivers of seedling diversity is required.  Using a chronosequence approach, permanent plots were established at 44 restored urban forests aged 5 to 59 years since initial plantings took place, across five New Zealand cities between Wellington and Invercargill. Vegetation surveys were undertaken and data on micro-climate were collected. This study examined the 1) temporal dynamics of restored urban forest development and seedling regeneration and 2) dominant drivers of seedling regeneration. Data were analysed using linear regression models, breakpoint analysis and mixed-effects modelling.  Early forest development (<20 years) exhibited the most changes in canopy composition and structure, forest floor dynamics, seedling community and microclimate. This period saw significant increases in canopy stem abundance, height, basal area and leaf litter cover. Significant declines occurred for light transmittance, herbaceous cover and daily soil and air temperature range within the same timeframe. Dominant traits amongst the seedling community included early successional species, tree species, shade and drought tolerant species, insect-pollinated species and frugivory dispersed species. Seedlings with these traits had higher species richness levels across the whole chronosequence.  Collectively, five biotic drivers representing forest composition, structure and landscape factors strongly influenced seedling diversity. Seedling diversity increased with the proportion of surrounding natural landcover, sapling diversity, basal area, canopy diversity and herbaceous cover. The influence of these predictors of seedling diversity, was more significant when modelled as a set, than when viewed independently. Geographic location (city) was indicated as a stronger predictor for similarities in canopy and seedling community composition than the age of the restoration planting. This was shown by stronger clustering of sites according to their city, more so than forest planting age, in a non-metric multidimensional scaling analysis.  Our results provide valuable insight to restoration practitioners on the outcomes of urban restoration programmes implemented across much of New Zealand and helps close the gap between the science of restoration ecology and the practice of ecological restoration.

History

Copyright Date

2019-01-01

Date of Award

2019-01-01

Publisher

Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline

Ecology and Biodiversity

Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level

Masters

Degree Name

Master of Science

ANZSRC Type Of Activity code

970106 Expanding Knowledge in the Biological Sciences

Victoria University of Wellington Item Type

Awarded Research Masters Thesis

Language

en_NZ

Victoria University of Wellington School

School of Biological Sciences

Advisors

Hartley, Stephen