Restoring native ecosystems in urban Auckland: urban soils, isolation, and weeds as impediments to forest establishment
- Bio-Protection Research Centre, PO Box 84, Lincoln University, Lincoln 7647, New Zealand
- Landcare Research, PO Box 40, Lincoln 7640, New Zealand
- Landcare Research, Private Bag 92170, Auckland Mail Centre, Auckland 1142, New Zealand
- Current address: QEII National Trust, PO Box 3341, Wellington, New Zealand
New Zealand urban environments are currently dominated by exotic plant species. Restoring native vegetation and its associated native biodiversity in these landscapes is desirable for both cultural and ecological reasons. We report on the first four years of an ongoing vegetation restoration experiment in Waitakere City, Auckland, that addresses four challenges to urban restoration: weeds, Anthropic Soils, attraction of frugivorous birds, and patch isolation. Nine commonly planted native species, grouped separately into wind- and bird-dispersed species, were planted across four sites increasingly isolated from native bush patches, using two site preparation methods. By year three, woody weeds >50 cm tall had established with an average density of 1.7 plant m-² across all sites. This was more than 17 times denser than all established wild native woody seedlings of any height. One of our establishment methods, sparse planting with mulch, resulted in higher native plant survival and faster plant growth. However, after 4 years, the more intensive method, dense planting and ripping of the soil, resulted in a denser canopy and a 2.8-fold reduction in woody weed establishment. The typically urban soils of all sites were highly modified, with substantial variation in compaction, ponding risk, and fertility over distances of 5–15 m. Several, but not all, species were detrimentally affected by soil compaction and ponding. Many bird-dispersed species, both native and non-native, colonised the experiment, although this did not differ between plots with planted wind-dispersed and bird-dispersed species, perhaps due to the small size of these plots. Site colonisation by native species was particularly high at sites ≤ 100 m from existing native vegetation, suggesting that even small patches of native vegetation in urban landscapes will be valuable as seed sources for accelerating native plant establishment at nearby receptive sites.