City Life Rewrites the Clocks of Tropical Trees, Two-Year Study Finds

In the tropical city of Recife, in northeastern Brazil, the same tree species that bloom and fruit on a predictable schedule in natural forests behave in strikingly different ways once they are planted in urban squares and parks. A new two-year study, published in the journal Discover Ecology, followed nearly a thousand adult trees across fourteen urban green spaces and compared their flowering and fruiting rhythms with the patterns reported for the same species in their natural habitats. The result is one of the clearest community-level demonstrations yet that urbanization does not merely shift the timing of plant reproduction by a few weeks. Instead, it can fundamentally reorganize the entire phenological pattern of tropical trees, changing how many times per year they flower, how intensely they fruit, and how synchronized their populations are.

The research team, led by Marcela T. P. Oliveira and Jéssica L. S. Silva of the Federal University of Pernambuco, monitored 955 individual trees representing 77 species from 21 botanical families. The study sites included ten public squares and four urban parks, together covering roughly forty percent of the total area of squares and parks in Recife, a city of about 1.5 million people that sits at the heart of the Pernambuco Endemism Center of the Atlantic Forest. Every month from June 2016 to May 2018, the researchers recorded the intensity of flowering and fruiting using a semi-quantitative scale that classifies each phenophase into five categories, from complete absence to full expression across the crown. They then classified each species by geographic origin, pollination system, and seed dispersal mode, allowing them to ask whether urbanization affects different functional groups of plants in different ways.

The first and perhaps most sobering finding concerns the composition of the urban tree flora itself. Seventy-eight percent of the species growing in Recife’s green spaces are exotic to the northeastern Brazilian Atlantic Forest. In the squares, only thirteen of seventy-one species were native to the region, and even in the parks, natives made up less than a quarter of the flora. This imbalance matters because the native species that are present do not represent the full functional breadth of the regional forest. The researchers found no native Atlantic Forest trees with specialized pollination systems at all: there were no native species pollinated by birds, hawkmoths, flies, wasps, or wind in any of the fourteen sites. The only native bat-pollinated tree recorded was Chloroleucon foliolosum, a legume, and the only native beetle-pollinated species was the palm Acrocomia intumescens.

This functional gap has direct consequences for urban wildlife. Specialized pollinators such as hummingbirds and sphingid hawkmoths depend on particular floral morphologies, nectar concentrations, and phenological windows that only certain native plants provide. When a city’s tree palette excludes those plants entirely, the specialist pollinators lose their resource base, no matter how many flowers bloom in the streets. The study’s authors argue that this absence of native resources for specialized vectors, combined with the altered phenology of the natives that do occur, negatively affects the maintenance of local faunal diversity. In other words, a green city is not automatically a biodiverse city; the identity and temporal behavior of the plants matter as much as their abundance.

The second major finding is that urban conditions change the reproductive calendars of the trees themselves. When the researchers compared the phenological patterns observed in Recife with those documented in the literature for the same species in natural ecosystems, they found that around seventy percent of the species for which comparative data existed had changed their flowering or fruiting patterns. The most common transition was from an annual pattern, meaning one reproductive event per year, to a sub-annual pattern, meaning more than one event per year. Forty-seven species changed their flowering pattern and forty-nine changed their fruiting pattern, and among the species that shifted, more than half were native to the northeastern Atlantic Forest. A chi-square test confirmed that this frequency of change was statistically significant.

Several concrete examples illustrate the scale of these shifts. Libidibia ferrea, a leguminous tree that flowers once a year in its natural habitat, flowered multiple times per year in Recife’s squares. Cenostigma pyramidale, which in the seasonally dry Caatinga blooms for a single four-month period, flowered continuously in the city. Sarcomphalus joazeiro, a fruiting tree of the Caatinga that produces fruit once a year in nature, fruited twice a year under urban conditions. The researchers suggest that for these species, many of which evolved under arid or seasonal conditions where water is limiting, the irrigated, nutrient-rich soils of urban parks remove the environmental constraints that normally synchronize their reproduction.

The mechanisms behind these phenological reorganizations are likely multiple and interacting. Urbanization generates heat islands, elevated concentrations of polluting gases, reduced humidity, drier soils in some contexts, altered nitrogen deposition, and reduced soil carbon, all of which can act as cues that modify plant phenological responses. At the same time, manual irrigation is common in Recife’s public squares and parks, effectively abolishing the dry season that structures reproduction in much of the regional flora. The result, at the community level, is a striking loss of seasonality: flowers were available in every month of the two-year study, and fruit was produced continuously except for a single species, Aspidosperma pyrifolium, which paused entirely. Only one species, the wind-pollinated exotic Casuarina equisetifolia, restricted its flowering to a defined five-month window.

Synchronization among individuals also told an important story. Using an index that accounts for both the intensity and the temporal overlap of phenophases, the researchers found that native trees showed lower flowering and fruiting synchrony than exotic trees. Species pollinated by birds, hawkmoths, and wasps, all of which were exclusively exotic, showed relatively high synchrony among individuals, whereas trees pollinated by bees and diverse small insects, including the natives, showed low synchrony. Fruiting synchrony was low across all dispersal modes, with values below 0.3 for animal-dispersed, self-dispersed, and wind-dispersed groups alike. Low synchrony means that individual trees in the same population are reproducing at different times, which can reduce the efficiency of pollinator-mediated pollen transfer and fragment the resource pulses that fruit-eating animals depend on.

The dominance of exotic species in shaping these urban phenological rhythms raises concerns that extend beyond the city limits. Exotic plants can compete with natives for shared pollinators, alter the abundance and composition of pollinator communities, and reduce the reproductive success of native species, particularly when flowering periods overlap. Dispersing animals often prefer the fruits of exotic species, which can further skew seed dispersal away from native trees. The authors also note subtler risks: the nectar or floral resources offered by some exotic ornamentals may be toxic or nutritionally inferior to those of native plants, potentially endangering pollinator health. Because the exotic species in Recife’s green spaces are more numerous and possess a wider range of reproductive strategies, they effectively command the community-level pattern of flowering and fruiting, setting the temporal template that native plants and animals must navigate.

The study’s practical message is directed at urban planners and arborists across the tropics. Urban afforestation programs, the authors argue, must prioritize native species from each phytogeographic domain and select a palette that makes floral and fruit resources available in a complementary way throughout the year, rather than relying on a handful of exotic ornamentals that produce a continuous but ecologically shallow resource stream. The historical roots of the problem run deep: much of the exotic flora in Brazilian cities traces back to colonial-era landscaping traditions, and even celebrated twentieth-century designs by the landscape architect Roberto Burle Marx, who created several of the squares studied here, favored showy plants from other Brazilian domains such as the Caatinga and the Amazon rather than the local Atlantic Forest. As climate change accelerates and cities continue to expand, long-term phenological monitoring will be essential to track how these urban plant communities respond, and to ensure that the green infrastructure of tropical cities supports, rather than undermines, the pollinators and seed dispersers on which both urban and natural ecosystems depend.

Subject of Research: Urbanization effects on the reproductive phenology of tropical tree species in urban green spaces compared with natural Atlantic Forest areas

Article Title: Same tree species, different reproductive phenological patterns between tropical urban green spaces and natural areas

Article References: Oliveira, M. T. P., Silva, J. L. S., Cruz-Neto, O., & Lopes, A. V. (2025). Same tree species, different reproductive phenological patterns between tropical urban green spaces and natural areas. Discover Ecology, 1(1), Article 13. https://doi.org/10.1007/s44396-025-00014-9

Image Credits: AI Generated

DOI: 10.1007/s44396-025-00014-9

Keywords: phenology, urban ecology, Atlantic Forest, pollination, flowering, fruiting, native species, exotic species, urban green spaces, tropical trees, seed dispersal, biodiversity