Ephemeral visitors or permanent residents? — Decadal change in the ruderal vegetation from a periurban university campus

Abstract

Urbanization creates environmental conditions that hinder the growth of natural vegetation. We surveyed the ruderal vegetation from a periurban university campus in west-central Mexico during the rainy seasons of 2008 and 2016–2018, time during which the campus underwent intensive construction. The built area grew from 4 ha in 2009 to 12.6 ha in 2017. We identified 234 different Angiosperms belonging to 165 genera and 43 families and the community composition changed over time. For example, Asteraceae was replaced by Poaceae as the richest family in 2018. Also, 16 native species found in 2008 disappeared from the study site, 9 of which have been related with low disturbance. In contrast, 98 new species were observed in the latter years, including some that are commonly found in cities. Overall, species richness increased with time, including that of exotic species that increased from 16 % of the total species in 2008 to 24 % in 2018. Thirteen of such exotic species are invasive in Mexico, including Digitaria velutina, Asphodelus fistulosus, Mercurialis annua, and Senecio inaequidens, for which this was their first record in the city of Morelia (population 849,053), where the campus is located. These results suggest that environmental conditions imposed by disturbance can favor the proliferation of various species, especially grasses and several exotic species of different families.