Urban trees in Niterói - Brazil: Invasive species report

Exotic species in Colonial Brazil

Being a colonized country, Brazil has faced, throughout the last five centuries at least, heavy exploitation of it's natural resources, regarded by some as the world's barn, Brazil derives a large portion of it's GDP from agricultural exports, most of which, if not all, are by-products of the monoculture of exotic species.

During it's colonization (1500-1815) period, many exotic invasive species of flora have been introduced, mainly by the metropolis (Portugal), while over-exploitation of the native species has led many to the brink of, if not full-on extinction, such as the tree from which the country's name derives from the native species, Pau-Brasil (Paubrasilia echinata), which has mostly been eradicated across Brazilian land.

In this study, i check just how greatly have exotic species taken root (pun unintended) in my city's urban trees.

Through a government project "Arboribus" i analysed geospatial data from across the city i live, Niterói, Rio de Janeiro, Brazil.

The analysis itself

Being a environmental sciences major, as soon as i found Arboribus's dataset, i managed to find a way to complain about the environment and how it's been dealt with, through recent studies of Python's modules, Pandas and GeoPandas, i had the perfect tools to properly analyse and illustrate relevant data within the dataset, which were plenty.

Utilizing Pandas's dataframes i broke down the data mainly in two categories: Native species and Exotic species.

From thus came the first shock in my studies, sadly, exotic trees already outnumbered the native ones, be it from human interference or purely exotic trees natural propagation capacities.

Out of nearly 60.000 trees, exotic species made up more than half of them (36417).

As a more clear example of how badly Niterói's flora has been disfigured, i'll compare two species, the aforementioned Pau-Brasil (Paubrasilia echinata) and one of the 100 worst invasive species (IUCN, 2000), Leucaena (Leucaena leucocephala).

Showdown

Home team first, Pau-Brasil:
Numbering 922 trees total out of 60.000, making up 1,53% of total trees

Secondly, Leucaena:
At 910 trees, Leucaena makes up 1,51% of total trees.

Interpretation

Although Leucaena trees are a bit less frequent, it's important to observe that Leucaena occurrence is more evenly spread across Niterói's territory than Pau-Brasil, which tends to concentrate around certain areas.

Not only that, two other factos weigh heavily:

1. As mentioned before, Leucaena is considered by International Union for Conservation of Nature (IUCN) as one of the 100 worst invasive species in the world, due to it's fast growth and frondous leaves, which tend to overcrowd other species of vegetation, enabling Leucaena to grow even more, due to little competition, leading to abundance of nutrients.

2. Arboribus checks in on urban trees, and urban trees alone, these trees are the ones the public powers have a easier time tending to, or cutting down in cases such as these, meaning that despite the prefecture uprooting (again, pun unintended) Leucaena invasion, it's still expressive in both numbers and area of occurrence, not to mention the possibility of Niterói's forests being more heavily invaded than the urban medium.

Conclusion

Despite the grim findings, it's been fun analysing geospatial data and interpreting it, hopefully with evolving technologies on remote sensoring and geoprocessing more studies such as these can be brought to authoritiess attention, enabling better, more precise responses to threats such as these.

Thank you for reading!

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