People, Cities & Nature
Planting of native species to restore forest in urban centres is an important conservation activity that has been gaining momentum in New Zealand for over 40 years. Early projects were few in number, largely isolated from each other, and weren’t based on scientific knowledge. In contrast, today's urban forest restoration projects are numerous, increasingly linked by conservation networks and knowledgeable communities, and are often on the cutting-edge of our ecological understanding.
Our Plantings research is addressing the demand for new information on best practice in urban ecological restoration to support these projects. We are studying plantings throughout nine New Zealand cities to better understand the requirements for efficiency and success of restoration efforts of city councils and community groups.
We want to discover the most efficient pathyway to restore an urban forest, from first plant in the ground, to a mature ecosystem that self-regenerates. There are two main ways we are doing this. First, we are using a nation-wide chronosequence approach, whereby space is substituted for time, for surveying to determine how regeneration dynamics of restoration plantings vary with microclimate and vegetation composition among cities. Second, we are planting and monitoring enrichment species such as rimu and tawa to test how to facilitate urban forest succession. Findings from this work will help to improve wildlife habitat and ecosystem service provision through successful restoration of long-lived, self-regenerating urban forests.
Vegetation & Environment Surveys Our surveys use permanent vegetation plots to quantify the structure, composition, and environmental conditions of urban vegetation. We have developed methods that will provide detailed understanding of the short-term (1-10 yrs) to medium-term (10-40 yrs) successional dynamics of restoration plantings. Our data help us answer questions like: when exactly does canopy closure occur so that competing weeds die back? and, which environmental conditions are most important for trees to regenerate successfully? Hard data on these important ecological processes is currently unavailable for New Zealand cities.
Understanding how light, microclimate, and understorey conditions change over the first 40 years of development will provide councils with critical information for long-term planning to maximise efficiency of resource allocation. City councils will be provided with improved restoration planting guidelines to maximise both immediate and long-term success of projects.
Enrichment Experiment In naturally functioning ecosystems, forests composed largely of sun-loving pioneer trees are normally replaced by late-successional shade-tolerant trees like rimu or tawa. These large, slow-growing trees often depend on birds (e.g., kererū, tūī) to disperse their seeds but in many of our towns and cities these birds are now absent and the late-successional trees are not returning to restored areas.
We know that facilitating forest succession by enriching restoration plantings with late-successional tree seedlings will speed the natural process of succession and provide habitat structure and food resources to bring back our iconic native birds. Aiding establishment of these late-successional trees is the final stage of stabilising young restored forests, ensuring they will last a long time without much need for maintenance or expense. Within forest plantings aged 5-40 years we will establish manipulative experiments to determine optimal conditions for introducing seedlings of late-successional canopy species and epiphytes.
Study sites The study sites for the Plantings research project are in nine cities: