Why urban greening requires more than just species biodiversity

Over the past decades, a noticeable shift has taken place in the relationship between humans and nature. There is a growing interest in re-naturalizing urban environments by increasing vegetation cover as a means to foster more resilient cities and enhance environmental comfort for urban dwellers. Numerous policy recommendations emphasize vague targets such as increasing urban biodiversity or expanding tree canopy cover. While these indicators are indeed relevant and contribute to ecosystem service provision, they remain insufficient as standalone goals, failing to account for the complexity of factors involved in the design and planning of green urban infrastructure. This article places particular emphasis on the role of trees as the core unit of green infrastructure. Other vegetative strata, such as herbaceous layers or vertical greening systems, are acknowledged but regarded as secondary or complementary to tree-based systems. We highlight the conceptual ambiguity surrounding terms like “biodiversity” or “canopy increase” and argue that these metrics, although widely used, must be subordinated to a more integrative and function-driven planning paradigm. Urban forestry strategies should not aim merely to boost biodiversity indices but rather to develop evidence-based planting proposals that consider plant functional traits, optimize ecosystem service delivery, minimize disservices, and ensure species selection aligns with future climate conditions. This also involves maximizing genetic diversity, conducting detailed assessments of below-ground conditions (soils), as well as canopy height and diameter class structures, to enhance resilience against pests and diseases. Furthermore, spatial distribution must be planned to ensure justice and equity across socioeconomic groups. Ultimately, fulfilling all these criteria is likely to result in more biodiverse urban forests, but this diversity will be the consequence of well-defined, objective, and scientifically grounded decisions, rather than an arbitrary increase in a metric whose optimal threshold remains undefined. The goal is not simply more biodiversity, but smarter, functionally informed biodiversity.