Urban greening is becoming a knowledge infrastructure before it becomes a coherent spatial infrastructure. Trees, gardens, corridors, green roofs, rain gardens and nature-based solutions enter the city through different disciplines, each carrying its own measures, thresholds, vocabularies and assumptions about what counts as success. The resulting landscape is not simply ecological. It is epistemic: a territory continuously produced through models, biodiversity indicators, health metrics, planning rules, participatory workshops, municipal procedures and claims about multifunctionality. What appears physically as green infrastructure is therefore also an arrangement of evidence. Its form depends on which variables are visible, which scales are selected, whose knowledge can enter decision-making and which benefits can be rendered sufficiently legible to justify intervention. This becomes clear when quantity gives way to relational structure. Hao et al. show that vegetation cannot be reduced to a percentage of green cover because structure, species and colour interact in non-additive ways. Gong et al. demonstrate that biodiversity does not act upon an abstract universal subject but is mediated by nature connectedness. Croeser et al. shift the problem again: the ecological value of a retrofit depends not merely on its area but on its position within networks of fragmentation and movement. These works collectively dismantle the idea that urban nature can be governed through a single metric. Ecological quality is compositional, perceptual and topological. The city cannot therefore be greened effectively by adding undifferentiated units of vegetation. It requires knowledge capable of distinguishing where, what kind, for whom, in relation to which system and according to which ecological process.

Multifunctionality intensifies the problem because every additional function requires another mode of seeing. Cook et al. reveal that engineered green infrastructure is still commonly discussed through water objectives while more natural forms are associated with biodiversity and wellbeing. The division is disciplinary before it is spatial. A rain garden, street tree or wetland may simultaneously alter hydrology, thermal comfort, habitat, public health and social use, yet institutional systems often perceive only the function assigned to the responsible department. Green infrastructure becomes genuinely multifunctional only when knowledge is coordinated before design. This makes interdisciplinarity an infrastructural requirement rather than an academic virtue. The difficulty is not that the city lacks ecological effects; it is that those effects are distributed across incompatible observational regimes. Co-production adds another layer by questioning who has authority to define the system in the first place. Pluchinotta et al. make urban natural space modelable through a participatory process in which maintenance, safety, accessibility, participation and awareness enter a shared causal structure. The model is valuable not because it perfectly represents the city but because it makes assumptions discussable. Simulation becomes a public epistemic interface. Hölscher et al. then show why this cannot remain a temporary research performance: cities need institutional capacities capable of embedding co-production into planning, delivery and stewardship. Egerer et al. locate a similar process in community gardens, where biodiversity knowledge is generated through cultivation, monitoring and collective experimentation. Knowledge here does not travel from laboratory to city in a one-way transfer. It emerges through situated interaction among residents, scientists, organisms, spaces and municipal structures.

Justice determines whether this expanded knowledge system genuinely becomes plural or merely appropriates plurality. Derickson et al. insist that urban greening must be analysed through histories of uneven urbanisation, power and scale, while researchers must recognise themselves as knowledge brokers rather than neutral producers. This reframes participation as an epistemic question. Communities do not simply contribute local detail to an already defined problem; they may contest the categories, scales and benefits through which the problem has been framed. The shift from “city” to “urbanisation” is especially important because ecological and infrastructural processes exceed administrative boundaries. Green interventions can redistribute value, risk and displacement across territories invisible to project-based evaluation. A justice-oriented green epistemology must therefore examine what its own maps omit. Evidence itself becomes an object of governance. Li et al. show that the apparent maturity of nature-based solutions conceals major weaknesses in baseline data, taxa coverage and comparative evaluation. Konijnendijk’s 3–30–300 rule presents the opposite epistemic operation: radical compression of heterogeneous evidence into a simple spatial standard. Both are necessary and dangerous. Without indicators, baselines and rules, urban ecological knowledge cannot travel into planning; without reflexivity, those devices can solidify partial evidence into universal prescriptions. The central task is not to choose between complexity and legibility but to construct reversible translations between them—standards that remain traceable to evidence, models that reveal assumptions, metrics that preserve context, and participatory processes whose outcomes can actually modify institutional action. Socioplastics can treat this entire field as a study of how distinctions become infrastructures. Biodiversity, connectivity, accessibility, multifunctionality, justice, restoration and participation are not merely themes attached to urban nature; each is a regime for seeing and organising relations. Their value lies in preserving differences while enabling crossings. A corpus built on these papers should therefore index not only authors and topics but epistemic operations: measurement, compression, modelling, co-production, targeting, comparison, brokerage, scaling and institutional embedding. Such an archive would make visible how a city learns to perceive its own ecological conditions and how those perceptions acquire material consequences. Green infrastructure then becomes inseparable from the infrastructures that decide what counts as green, what counts as evidence and whose knowledge is authorised to alter space. The strongest contribution of this field is the recognition that ecological transformation is simultaneously a transformation of the regimes through which urban reality is known; within Socioplastics, that shift condenses as RegimeMutation.