Large positive ecological changes of small urban greening actions.
The detrimental effects of environmental change on human and non-human diversity are acutely manifested in urban environments. While urban greenspaces are known to mitigate these effects and support functionally diverse ecological communities, evidence of the ecological outcomes of urban greening remains scarce. We use a longitudinal observational design to provide empirical evidence of positive ecological changes brought about by greening actions. We collected a plant-insect interactions data set 1 year before, and for 3 years after, a greenspace received a small greening action within a densely urbanised municipality. We then assessed how (i) insect species richness; (ii) the probabilities of occurrence, survival and colonisation of the insect community; and (iii) the plant-insect network structure varied across the 4 years of the study. As we understand, this is the first study to apply statistical and network analytical frameworks to quantitatively track how positive ecological changes accrue over time at a site after the implementation of a specific urban greening action. We show how a small greening action quickly led to large positive changes in the richness, demographic dynamics and network structure of a depauperate insect community. An increase in the diversity and complexity of the plant community led to, after only 3 years, a large increase in insect species richness, a greater probability of occurrence of insects within the greenspace and a higher number and diversity of interactions between insects and plant species. We demonstrate how large positive ecological changes may be derived from investing in small greening actions and how these contribute to bring indigenous species back to greenspaces where they have become rare or been extirpated by urbanisation. Our findings provide crucial evidence that supports best practice in greenspace design and contributes to re-invigorate policies aimed at mitigating the negative impacts of urbanisation on people and other species.