To talk about biodiversity it is first necessary to understand what biodiversity is. According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), biodiversity is all living organisms and the ecosystems of which they are part.
When we hear the word biodiversity it immediately brings to mind exotic places, many of which are in a pristine state, where there is a huge variety of plant species of different sizes and that provide habitat for incredible animals, from big cats to the most lethal insect. But it is not necessary to travel so far to enjoy biodiversity and we can in fact enjoy it right on our doorstep thanks to urban biodiversity, which includes all of the living organisms and ecosystems that are found in urban environments.
Urban areas currently occupy a large proportion of the earth's surface. Fifty six per cent of the earth's surface is urbanised, with 2.5% of Spain's area occupied by urban land, a percentage that is expected to increase as a result of population growth and the increasing movement of people from the countryside to cities (UN-Habitat, 2022; SEO/Birdlife, 2019). Changes in land use and habitat loss and fragmentation caused by cities are among the main causes of biodiversity loss.
Species living in urban ecosystems experience numerous difficulties every day in performing their vital functions. The presence of buildings and roads affects species that move on the ground. The excessive management of green areas such as the pruning and mowing of vegetation and the removal of dead wood, entails the loss of shelter and nesting areas, as well as feeding and foraging spots, for both birds and insects.
In addition to the changes caused by building and the maintenance of parks and gardens is the urban metabolism itself, which includes multiple chemical, sound and light pollution processes that change the biorhythms of many species and even alter their ability to reproduce.
If we add to this the effects of climate change that are more obvious in cities, such as the increase in temperature or the lower water availability, we see that these ecosystems can be truly hostile, for both urban flora and fauna. Even so, there are many species that manage to survive this change and adapt to new conditions.
As in most terrestrial ecosystems, plant communities are a key part of urban ecosystems, as they are the primary producers and the base of the urban trophic pyramid.
In cities there is a characteristic not found in other systems, with plant diversity mostly made up of ornamental species. From the urban trees, present in the parks and gardens and in the streets, to the plants that adorn roundabouts and central reservations, and flower beds, terraces and balconies in homes. Almost all of these plants are different from those we would find in a rural environment of our country. However, these plant species fulfil their role as food and shelter for urban fauna and are the ones that largely structure urban ecosystems.
In addition, in urban and peri-urban areas there are spaces that are key to biodiversity such as abandoned or vacant lots. These spaces host biodiversity that grows spontaneously. This normally comprises native plants that have escaped from natural areas and which end up becoming established in cities.
These patches of vegetation, together with the green areas, provide habitat for numerous animal species. Within the urban fauna we can find birds, mammals, reptiles, insects and even amphibians. Who has not taken an interest in the lizards that hide in the cracks of buildings, tried to catch a butterfly, observed the endless pathways of ants that form in spring or fled from a wasp in summer?