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Taking species knowledge from Mexico around the world

by Matt Downs

Elisa Olivares, Planting Design Lecturer at Capel Manor College in Regents Park, explains how work by Biologist Jerónimo Reyes and his team in Mexico is reaping rewards with regards to drought tolerant species and other planting selection further afield…

In the heart of Mexico City, guarded by the National Autonomous University of Mexico (UNAM) we find the Ecological Reserve of the Pedregal of San Angel. Since 1983, the University, the biggest in Latin America, has been committed to protecting 237 hectares,  equivalent to 30% of the territory of its vast University campus. 

The reserve is home to a host of vegetal communities that slowly colonised  exposed niches on top of lava rock after the volcano Xitle erupted more than 1,500 years ago. It consists of a  scrub community dominated by Pittocaulon praecox (Repsa, 2022), growing along with several species of cacti, crassulaceae, and geophytes like Sprekelia formosissima.

Green roof 150mm substrate in UNAM campus blending with the landscape of tree canopies in Mexico City.

At the edge of the reserve is the Botanic Garden of UNAM’s Institute of Biology, where the renowned Biologist Jerónimo Reyes and his team manage and nurture the National Collection of the Crassulaceae Family and the program of propagation and cultivation of cacti and succulents at risk of extinction. 

A central part of their mission is the collection of wild material for their ex situ conservation efforts and for national seedbanks. Jeronimo and his team have described many new species from the Cactaceae and Crassulaceae family and have collected and described several species of Dahlia new to science. Among their other activities, they also train small rural and urban nurseries to propagate endangered plants to sell, reducing the incentive for illegal collection, and to promote reintroduction into the wild.

Because of his great experience with drought-tolerant species, in the 1980s Jeronimo Reyes, along with other researchers, was invited by the federal government of Mexico to visit Germany to learn about green roof technologies. Since then, Reyes’s group has innovated in the fields of green roofs and green walls in Mexico, using a variety of drought tolerant species and designing a wide range of solutions for a climate that has very dry winters and very wet summers. His team also advises on green roof standards and regulations for Mexico, promotes the use of native species, and gives workshops on the installation and maintenance of green roofs. 

Experimental trial in Mexico with native Crassulaceae species.

When I did my doctoral research at the University of Sheffield’s Department of Landscape with Professor Nigel Dunnett, Reyes and his team advised me, trained me, and helped me to gather data on the use of Mexican Crassulaceae species in Mexico and in the UK. At Sheffield I was able to test Mexican species from different localities, donated by the Botanical Garden and exported to the UK with no soil and with stringent phytosanitary certification. Other Mexican species were donated by the UK’s National Collection of Sedum curated by Mr. Ray Stephenson, all material carefully provenanced and with collection data. Site collection data is of vital importance to understand which plant material will be able to cope with the new climate change challenges; by knowing geographical origins we may begin to infer suitable genetic adaptations.

 Mexican species of the Crassulaceae family in Sheffield 2014.

Today, we know that monoculture Sedum green roofs are not biodiverse green roofs, and that they do not provide the large amount of services we require nowadays from our green infrastructure. Nevertheless, species of the Crassulaceae family can still be used in green roof mixes. The flowers of Sedum, Echeveria, Graptopetalum, and Pachyphytum species provide nectar to pollinators, and can grow in the shallow substrates of a biodiverse roof. Their different structures and heights help enhance the topography and diversity of green roofs. 

Mexico is a biodiverse country, a megadiverse country in fact, with extraordinary levels of endemism. Its high number of unique plant species from vastly different climatic regions makes it an ideal source of novelty for green roof plants. Researchers like Reyes and his team are key players in this quest for specific plant species from those extreme microclimates that can thrive in urban green areas and provide a range of environmental services. Currently, Reyes and his team are collecting native plant material from the Valley of Mexico (where Mexico City is located), from trees to herbaceous plants. They are starting to propagate this germplasm to develop their ex situ collections and for its use in the local urban landscape by the Mexican government, property developers, and citizens interested in their use and rescue. This work does not only have an immediate impact in one city or in one region, in the face of global climate change its beneficial impacts will be spread across the world. 

Elisa Olivares is Planting Design Lecturer at Capel Manor College. Email Elisa at: elisa.olivares@capel.ac.uk

References:

REPSA, 2022. El Pedregal. [On line].
[Accessed: 15th January 2021] Available from: http://www.repsa.unam.mx/index.php/pedregal-de-san-angel 

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