Waiwhakareke Natural Heritage Park 2021 Long-term monitoring: Report on ecological restoration progress

This report was requested by Tui 2000 Inc. and the Hamilton City Council (HCC) as a means of tracking terrestrial restoration progress at Waiwhakareke Natural Heritage Park (WNHP). WNHP is a cutting-edge urban ecological restoration project in which ecosystems representative of the Hamilton Ecological District are being reconstructed from scratch on public land in Kirikiriroa Hamilton. Larger-scale projects of this nature are becoming more commonplace around the globe due to growing emphasis on restoring nature in urban areas. While this report quantifies the remarkable restoration success achieved at WNHP through investments by Tui 2000 Inc., HCC and the community since 2004, it also contributes to scientific theory. Restoration ecology is a newly developing scientific field and hence WNHP presents a unique opportunity for ecologists to improve restoration practice and also learn from the results. Here we share results from data analysed from 25 permanent monitoring plots throughout WNHP, spanning planting years since the beginning of planting in 2004 through to 2017 (14 years of planting). These plots are located across the five main ecosystem types (i.e., planting zones) being restored. This information should be used to inform current management and future planning for WNHP. In the 2021 monitoring, we measured key variables of forest development, including: canopy openness, native tree basal area, non-native herbaceous groundcover, leaf litter, dead trees, native tree seedling abundance and species richness, and epiphyte colonisation. Linear regression models revealed a statistically significant relationship between all (except dead trees and native tree seedling abundance) of these ecosystem variables and forest age. We note that there are several thresholds between 12 - 16 years since the initial restoration planting: basal area increased and the canopy openness decreased, reducing the light availability at the forest floor, thus reducing the non-native herbaceous groundcover from 100% to ~25% in 12 years (with one plot having 0% cover). With these ecosystem changes, important indicators of functioning forests appeared around the same time, such as leaf litter accrual (up to 95% groundcover) and an increasing number of dead trees (up to 37 dead small trees in one monitoring plot), native seedling recruitment (in abundance and species richness), and fern cover. The results in the report generally signal positive restoration progress. Now a focus is required on non-native weed and invasive mammalian pest control management, paired with careful enrichment planting, and where needed, infill of mid/late-successional plants. Enrichment planting and weed/pest management will help secure the investment in initial plantings by starting the longer-term next phase of forest development, while also creating a more species-diverse ecosystem, resilient to the manifold pressures of the urban landscape, disease, and climate change