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Towns with older human population and warm winters have a greater presence of non-native species in urban parks

El ciprés común (Cupressus sempervirens), la especie más frecuente, presente en casi el 70 % de los parques estudiados. Fotografía: A. Bayón (CC BY-SA 4.0).

A study led by the Doñana Biological Station (EBD-CSIC) and the University of Cádiz (UCA) concludes that the proportion of non-native species in urban parks increases with older human population and higher difference between summer and winter temperatures. This study has been carried out in collaboration with the University of Constance (Germany).

The research group, led by Montserrat Vilà from the EBD-CSIC and Óscar Godoy from the UCA, has studied how the climatic and socioeconomic conditions of cities can influence the traits of species planted in urban parks and the proportion of established non-native species. To do this, they have analyzed 46 urban parks and gardens distributed in 23 towns across the Spanish peninsular territory.

Dr. Álvaro Bayón from the EBD-CSIC, first author of the study, points out that "400 out of the 486 species found in these parks and gardens were non-native". Among them, there are the Mediterranean crypress (Cupressus sempervirens), native to the eastern coasts of the Mediterranean Sea and naturalized in practically the whole Iberian Peninsula, or the black locust (Robinia pseudoacacia), native to the eastern United States and an invasive species in Spain. Bayon highlights the need to include both these and other invasive species planted in urban parks in the Spanish regulation and regrets that these trees continue to be present in more than half of the parks studied.

Among the most relevant results when analysing plant traits, the study stands out the presence of plants with large and beautiful flowers in places with warm winters. The researchers considers that this effect is due to the preference for these aesthetic traits in towns where winters are milder.

During the study, they have also found relationships between the presence of non-native plant species and demographic factors. Specifically, the scientists indicate that the proportion of non-native plant species increases with older human population and bigger homes. "In the Doña Casilda Iturrizar park in Bilbao, where the median age is 46 years old, four years above the average of the towns studied, we have up to 86% of non-native species", Bayon explains, "On the contrary, the Jarama Park, in Coslada, where the median age is only 39 years old, had only 29% of non-native species".

Although it is true that young people tend to be more concerned about the environment, it is also true that exotic trees are very popular. However, the general population does not usually play an active role in making decisions about which species to plant. Therefore, the scientific team think that more precise sociological analyses are needed to find the underlying causes of these correlations.

On the other hand, they have also verified that there is a relationship between the annual range of temperatures - the difference in temperatures between winter and summer - and the proportion of naturalized exotic species, that is, that are already established in the natural environment. "Among the parks studied, those where the proportion of non-native species established is higher is San Francisco, in León, where 100% of the non-native plants are established, and Delicias de Arjona in Seville, where 88% are established, both cities with a high temperature range", indicates Godoy. "In areas that have a temperature range below the average, such as Pamplona, ??they tend to have parks with a lower proportion of non-native species, such as Yamaguchi Park, with 35% of the non-native established, or the "Enamorados" park with 29%".

"These results," says Vilà, "offer basic data to understand and predict the establishment of plants introduced as ornamentals, and will help us improve prevention systems to avoid future biological invasions."

Reference:

Bayón et al. 2021. Proportion of non-native plants in urban parks correlates with climate, socioeconomic factors and plant traits. Urban Forestry & Urban Greening. DOI: https://doi.org/10.1016/j.ufug.2021.127215

 

Read press release (Spanish): 


https://doi.org/10.1016/j.ufug.2021.127215