The urban forest as a mirror of inequality: plant diversity, ecosystem services, and social valuation in Xalapa, Mexico

Cities are often seen as concrete jungles where nature struggles to survive, but in reality, they are complex ecosystems where trees, people, and the economy are deeply intertwined. In many parts of the world, the distribution of green space is not random; it often mirrors the wealth of the neighborhood. Wealthier areas tend to have more trees, and those trees are often different from the ones found in poorer areas. This phenomenon, sometimes called the "luxury effect," suggests that money buys not just better housing, but a different kind of nature. However, this relationship is not just about how many trees there are. It is also about what those trees do for the people living around them. Do they provide shade and fruit for survival, or are they planted for their beauty? And do the trees themselves support other life, like the small plants that grow on their branches without harming them? Understanding these dynamics is crucial because the way we manage our urban forests can either deepen social divides or help heal them.

In the city of Xalapa, Mexico, a team of researchers set out to see how these dynamics play out in a real, living city. Xalapa is a mid-sized city nestled in a region of high biological diversity, where the urban landscape is a patchwork of parks, private gardens, and older neighborhoods. The researchers wanted to know if the level of poverty in a neighborhood changed the types of trees present, the variety of life those trees supported, and how the local people valued them. They walked through twenty different sites across the city, ranging from very wealthy areas to a single, deeply marginalized neighborhood on the edge of town. At each site, they counted every tree, measured its size, and noted what kind of species it was. They also looked up into the branches to count the vascular epiphytes—plants like ferns and bromeliads that live on trees but do not steal their nutrients. To understand the human side of the equation, they spoke with 164 residents, asking what they thought about the trees, what they used them for, and what they feared about them.

The study revealed a surprising pattern that challenges the simple idea that poverty always means less nature. The researchers found that the number of native tree species was roughly the same in rich and poor neighborhoods. The difference lay in the exotic trees. In the wealthier areas, residents had added a significant number of non-native, ornamental species to their landscapes, creating a "garden effect" where the total variety of trees was much higher. In contrast, the most vulnerable neighborhood had very few exotic trees, relying almost entirely on the native species that were already there. This created a mismatch: while the wealthy had a mix of native and exotic trees that matched their aesthetic preferences, the residents in the poorest area wanted trees that could provide food, medicine, or shade for daily survival, but the existing urban forest did not offer enough of these useful species. The trees were there, but they were not the right kind for the needs of the people living among them.

When the researchers looked at the plants growing on the tree branches, they found that the size of the tree mattered far more than the wealth of the neighborhood. The larger the tree trunk, the more epiphytes it could support. This is because large trees are usually older and have had more time to accumulate these small plants. Interestingly, the type of tree also played a role; native trees supported about seventeen percent more of these epiphytes than the exotic ones found in wealthier gardens. This suggests that the exotic trees, often chosen for their smooth bark and neat appearance, are actually less hospitable to the diverse life that thrives on native species. The researchers also discovered that the poverty level of a neighborhood did not directly determine how many epiphytes were present. Instead, the type of land use was the deciding factor. For example, areas used for livestock grazing, often found on the outskirts of the city, acted as unexpected havens for these plants because the trees there were left to grow large and were pruned only for safety or utility, not for looks.

The way people valued the trees shifted dramatically depending on where they lived. In the wealthier parts of the city, residents spoke about the trees in terms of beauty, recreation, and health. They saw the forest as a place to enjoy and a source of fresh air. But as the researchers moved toward the most marginalized site, the conversation changed. There, the value of the trees was practical and urgent. Residents focused on the ability of trees to provide fruit, water, and materials for building or fencing. They were less concerned with aesthetics and more concerned with survival. This difference in perception meant that even though the physical amount of carbon stored or water absorbed by the trees was similar across the city, the social value of those services was entirely different. A tree that provides shade in a wealthy park is a luxury; a tree that provides fruit in a poor neighborhood is a necessity.

The study also uncovered hidden risks that people often overlook. While residents in both rich and poor areas worried about branches falling, the reasons were different. Wealthier residents feared damage to their expensive infrastructure, while those in poor areas feared for the safety of their fragile homes. A more subtle danger was the confusion between harmless epiphytes and actual parasitic plants. About fifteen percent of the people interviewed thought the beautiful plants growing on the trees were parasites that needed to be cut down. This misunderstanding could lead to unnecessary pruning that destroys habitats for birds and insects. Furthermore, the researchers found a chemical risk that no one noticed. Trees in the wealthier areas, which included species that release natural gases, were located near heavy traffic. This combination could create a chemical reaction in the air that harms human health. In the poorest area, the trees released even more of these gases, but because there was almost no traffic, the dangerous chemical reaction did not happen.

The findings from Xalapa suggest that managing a city's forest cannot be done with a single plan for everyone. A strategy that works for a wealthy neighborhood might fail or even harm a poorer one. In areas of high poverty, the priority should be protecting the large, native trees that already exist and planting new ones that provide food and medicine. In wealthier areas, the focus should shift to understanding that the "perfect" look of a tree might come at the cost of the biodiversity it supports, and that the trees chosen for their beauty might inadvertently contribute to air pollution when combined with traffic. The urban forest is not just a backdrop for city life; it is a reflection of the social inequalities within it. By recognizing these differences, city planners and residents can begin to create green spaces that are not only beautiful but also fair, ensuring that every neighborhood has access to the specific benefits its community needs most.