A nation-wide urban trial network of tree and shrub climate resilience

Urban forests are widely recognised as a nature-based solution to mitigate the effects of climate change; however, urban forests are also vulnerable to climate change. Therefore, there is a need to improve species selection to ensure the delivery of ecosystem services by urban forests now and in the future. Research on the impacts of climate change on urban forests requires investigation to capture the complexities associated with species identity and growing conditions. Yet, such studies remain rare in urban contexts, highlighting the need for expanding collaborative research in cities. Here, we present a nation-wide urban trial network established across four states in Australia, showcasing stakeholder collaboration aimed at advancing urban forest research. The network consists of 11 standardised plantings of tree and/or shrub species aimed at testing species' growth and performance (i.e., stress tolerance) in cities across a range of climatic conditions. To test these differences, we measured height and diameter relative growth rates (RGR) and leaf damage caused by stress at each site one month after planting (2018-2020) and at the end of the austral summer in 2024. We used generalised linear mixed-effects models for RGR and ordinal logistic regressions for leaf damage to test the effects of annual maximum temperature (TMAX) and the Pinna Combinative Index (IP, a climate-drought index). By 2024, across all sites, we found 23 % of the originally planted individuals had died or were missing. We recorded significant differences in height and diameter RGR and leaf damage among sites, and IP was significantly and negatively related to both RGR and leaf damage. The network serves as an example of how stakeholder collaboration can broaden the scope of urban forest research that evaluates plant growth and performance across regions and environmental conditions.