Paved California Is Quietly Erasing Its Fungi, Community Science Data Reveal

California’s sprawling cities may be doing more damage to the state’s ecosystems than meets the eye, and the evidence is coming from an unlikely source: thousands of amateur mushroom hunters. A new study published in Ecology and Evolution has harnessed a decade of community science observations to reveal that impervious surfaces such as concrete and asphalt are associated with measurable losses in fungal diversity across the Golden State. The findings suggest that urbanization is not only shrinking the number of fungal species in affected areas but also homogenizing entire communities, replacing locally distinct assemblages of decomposers and symbionts with a smaller, more uniform set of urban survivors.

The research, led by Ariel Levi Simons along with Christopher Timlin-Broussard, Avicka Willis, and Jerelyn Lee, tackles one of the most persistent blind spots in urban ecology. Fungi underpin nearly every terrestrial ecosystem, decomposing organic matter, cycling nutrients, forming mycorrhizal partnerships with plants, and even acting as pathogens that shape community structure. Yet despite this ecological centrality, fungi remain chronically understudied in biodiversity monitoring, and their responses to urban stressors have been documented far less thoroughly than those of birds, mammals, or flowering plants. The new study demonstrates that publicly archived community science data can begin to close that gap at a spatial scale no single research project could achieve.

To measure urbanization, the team turned to the National Land Cover Database, which classifies every 30-meter pixel of the continental United States by the fraction of its area covered by surfaces impervious to water flow. This metric serves as a proxy for the hallmark of urban development: sealed ground. When rain cannot infiltrate soil, nutrient flows are disrupted, runoff accelerates, and groundwater recharge plummets. Previous research has shown that surface runoff can double when just 10 to 20 percent of a landscape is paved, and that groundwater recharge in urbanized areas can drop by as much as half. For soil-dwelling organisms, these hydrological upheavals fundamentally alter the resource base on which communities depend.

The fungal observations came from the Global Biodiversity Information Facility, or GBIF, an open archive where community scientists and researchers deposit species records. The researchers extracted every fungal occurrence recorded in California between 2015 and 2024, an initial haul of more than 342,000 records. After filtering to retain only species-level identifications, the dataset still contained nearly 300,000 occurrences, overwhelmingly contributed by human observers. Each record was then assigned to an ecological guild, or trophic mode, using the FUNGuild tool, sorting the fungi into pathotrophs, saprotrophs, and symbiotrophs. Ambiguous assignments and low-confidence classifications were discarded, leaving roughly 180,000 occurrences with clear ecological roles.

Working with opportunistically collected data requires statistical care, because sampling effort varies wildly across space and time. The team addressed this by estimating sample coverage for each putative assemblage, defined as all occurrences within a single imperviousness pixel in a given year and trophic mode, using the iNEXT framework. Only assemblages meeting coverage thresholds of 70, 80, or 90 percent were retained for analysis, a stringent filter that reduced the dataset to between roughly 1,700 and 499 assemblages and about 10,000 occurrences at the strictest threshold. Species richness, the study’s measure of alpha diversity, was then estimated by tracking the asymptotic behavior of richness against sampling effort, with rare species weighted equally to guard against undercounting.

The results paint a nuanced picture. For saprotrophic fungi, the decomposers that break down dead organic matter, estimated richness declined significantly with increasing impervious coverage, though the signal emerged clearly only at the strictest 90 percent coverage threshold. Notably, most of this decline appears to occur as soon as any impervious surface is recorded in the immediate vicinity, suggesting that even modest sealing of the ground may push fungal communities past an ecological threshold. However, when the researchers compared assemblages in areas with and without any impervious cover using nonparametric rank-sum tests, the difference in richness did not reach statistical significance, a reminder of how sensitive such analyses are to sample size and distributional skew. The data were heavily skewed toward unpaved areas, with skewness values rising from 1.64 before filtering to 1.87 after, reflecting a well-documented tendency of community scientists to record species in natural areas rather than city centers.

The more striking and consistent finding concerned beta diversity, the variation in community composition from place to place. For both saprotrophic and symbiotrophic fungi, the dispersion of beta diversity, measured as the average distance of assemblages from a group centroid in Jaccard dissimilarity space, declined significantly with increasing impervious coverage across all coverage thresholds. When assemblages from paved and unpaved areas were compared directly, the declines in dispersion were highly significant, with p-values as low as 10 to the power of negative 15 for saprotrophs and 10 to the power of negative 7 for symbiotrophs. In plain terms, fungal communities in paved landscapes are significantly more similar to one another than those in unsealed habitats, a signature of biotic homogenization. Pathotrophic fungi showed no such pattern, though the authors caution that the small number of recorded occurrences makes it impossible to distinguish a true ecological signal from a statistical artifact.

Why would urbanization flatten the differences between fungal communities? The authors propose ecological filtering as a central mechanism. The mechanical and chemical disturbances associated with development, from soil compaction to heavy metal runoff from roads, impose a narrow set of stresses that only a subset of species can tolerate. Land conversion disrupts the intricate architecture of mycorrhizal networks, while the urban heat-island effect alters temperature and rainfall regimes known to drive fungal richness. Compounding this, urbanization transforms plant communities, replacing native vegetation with a cosmopolitan suite of non-native ornamentals, and each plant community carries its own fungal symbionts. The massive transport of soil that accompanies construction may further homogenize underground communities by mixing propagules across regions. The result is a distinctly urban fungal flora, filtered from a once-diverse regional pool.

The study also underscores both the promise and the pitfalls of community science as a biodiversity monitoring tool. The fungal records were dominated by two phyla, Ascomycota and Basidiomycota, and by saprotrophic and symbiotrophic species, biases that mirror the tendency of amateur mycologists to document mushrooms with conspicuous, easily identified fruiting bodies. Microscopic fungi, aquatic chytrids, and arbuscular mycorrhizal Glomeromycota barely registered. Seasonal fruiting patterns were also obscured by the annual aggregation of records. Yet the sheer volume of data, growing year over year, proved sufficient to test the study’s central hypotheses at the scale of an entire US state, something previously feasible only with intensive DNA-based surveys.

Looking ahead, the authors argue that the era of molecular monitoring is poised to transform fungal conservation. Environmental DNA sampling can resolve species that never produce visible mushrooms, detecting microscopic inhabitants of soil that escape human observation entirely, and fungal datasets are expected to expand rapidly in both volume and taxonomic resolution. As urban land cover continues its global expansion, the California findings offer a warning and a template: the invisible kingdom beneath our feet responds to pavement in measurable ways, and with the right tools, we can now track it. Whether that tracking translates into protection for urban soil communities remains one of the defining ecological challenges of the century ahead.

Subject of Research: Effects of impervious urban surfaces on fungal richness and beta diversity in California

Article Title: Evidence for Reductions in Fungal Richness and Beta Diversity Dispersion Associated With Impervious Surfaces in California

Article References: Simons, A. L., Timlin‐Broussard, C., Willis, A., & Lee, J. (2026). Evidence for Reductions in Fungal Richness and Beta Diversity Dispersion Associated With Impervious Surfaces in California. Ecology and Evolution, 16(10), Article e74448. https://doi.org/10.1002/ece3.74448

Image Credits: AI Generated

DOI: 10.1002/ece3.74448

Keywords: urbanization, fungi, biodiversity, impervious surfaces, community science, GBIF, beta diversity, mycology, California, ecological homogenization, soil ecology, citizen science