Native or exotic species? Why the answer should not be binary

The choice between native and exotic species should not be binary. Natives suited to the place are an important base, for their ecological relationships and their link to the landscape, but the project also needs to consider soil, future climate, scale, function, invasive risk and performance on site. Exotic species should only be used when they are not invasive and when their function is clearly justified.

A species native to Portugal may not occur naturally in the region of the project, or may depend on conditions very different from those found in an urban courtyard. Equally, a non-native species may be well adapted and show no invasive behaviour. Status should be checked, but it does not replace a diagnosis of the site.

Selection needs to bring together origin, ecology, water availability, soil, temperature, rooting space, maintenance and function.

Native plants tend to take part in evolutionary relationships with local fauna, fungi and other organisms. Studies in different contexts show that origin can influence the abundance of invertebrates and the support given to food chains.

This advantage is not uniform across all species, and it does not mean that a native plant will work in any conditions. The structure of the garden and the surrounding landscape count too.

Before using an exotic, you should confirm whether the species appears on the National List of Invasive Species or on the Union List. In Portugal, Decree-Law no. 92/2019 prohibits the keeping, cultivation, trade and release into the wild of the species on the national list. The European list was updated again in 2025.

Even when the species is legal, it is worth assessing fertility, dispersal capacity and regional behaviour. Absence from a list is not an absolute guarantee of low risk.

The most common mistakes are calling a species native simply because it occurs in Europe; using an exotic without checking the law; assuming that origin guarantees urban adaptation; and reducing biodiversity to a label of provenance.

At Diaplant, origin is one of the selection criteria, alongside adaptation, function, future climate and invasive risk. Suitable native species form the base; other non-invasive species come in when they meet a specific need.

A mature decision does not pick a side. It prioritises suitable natives, excludes invasives and admits other species when they fulfil a function without increasing risk.

• Contrasting effects of tree origin and urbanization on invertebrate abundance and tree phenology. (2021).
• Trillo, A. et al. Year-round pollinator visitation of ornamental plants in Mediterranean urban parks. (2026).
• Flora-On — Flora de Portugal interativa. Sociedade Portuguesa de Botânica. (2025).
• Decreto-Lei n.º 92/2019, de 10 de julho. (2019).
• European Commission. Invasive alien species; Union List updated by Implementing Regulation (EU) 2025/1422. (2025).
• Forest Research. Urban Tree Manual. (2018).