Urban home yards rewilded: may benefit microbiome and inflammatory response in just three months, neighborhood deadwood also played a role

A recent Finnish study has found that rewilding residential yards affected the skin and oral microbiota of residents and was linked to the body’s inflammatory responses. Furthermore, the amount of decaying deadwood in the surrounding neighborhood was associated with the composition and function of the human microbiome. This highlights deadwood as a potential new indicator for environmental health.

Urbanization and biodiversity loss have reduced human contact with the diverse microbiomes found in natural environments. Exposure to environmental microbes supports the normal development and regulation of the immune system. This reduction in exposure is considered a contributing factor to the rising prevalence of allergies, asthma, type 1 diabetes, and other immune-mediated diseases. According to the new study, rewilding home yards can diversify the skin and oral microbiota of residents and correlate with the body’s inflammatory response. The study also revealed that the amount of deadwood in the neighborhood was linked to the composition and metabolic pathways of the human microbiome.

“This newly published study conducted in urban yards is the first to show that the effects of yard rewilding and gardening practices can extend from one’s own home garden all the way to the human microbiome and the functioning of the immune system. What is also unique is that the amount of decaying deadwood in the neighborhood was associated with the human microbiome and its metabolic pathways,” says leading researcher Aki Sinkkonen from the University of Eastern Finland.

The study was published in the prestigious international scientific journal Microbiome. The research included 36 detached house yards. Out of these, 21 yards were modified to be more natural by introducing diverse vegetation, deadwood, wood chips, microbially rich growing media, and leaf composters. Participants with rewilded yards were also instructed to practice benign neglect, such as leaving autumn leaves to decompose instead of raking them and converting lawn areas into meadows. In the control group of 15 yards, garden care was continued as usual. The participants were already active gardeners before the study began.

Postdoctoral researcher and teacher Laura Uimonen from Tampere University designed the yard modifications together with the residents, aligning them with the research goals. A standardized template was used for every yard, where the placement of green elements was decided in collaboration with the residents.

“The enthusiasm of the residents was one of the project’s greatest strengths. Co-designing helped create yards that supported both biodiversity and the goals of the study. It was highly rewarding to see how people embraced the rewilded areas and followed their development as part of their daily lives!” Uimonen praises.

Effects of a rewilded yard visible in the skin microbiome

The participants’ skin and oral microbiota, as well as salivary inflammatory mediators, were monitored for three months. The diversity of the skin microbiome was preserved further into autumn among residents of the rewilded yards compared to those with control yards, even though time spent outdoors decreased in both groups. Bacteria typically associated with natural environments increased particularly on the skin of residents with rewilded yards, while the relative abundance of bacteria linked to infections decreased. The results suggest that adding microbially diverse natural elements near walkways and seating areas can increase contact with environmental microbes, thereby influencing the skin microbiome.

“It was particularly interesting that the differences between the groups emerged even though gardening was practiced in both groups and the time spent in the yard decreased towards autumn. The results suggest that it is not just about how much time you spend working in the yard, but also what kind of yard surrounds us. A wild, more natural yard with its deadwood and so-called benign neglect can provide a more diverse microbial exposure than a traditionally maintained yard,” explains the study’s lead author, Marja Roslund from the Natural Resources Institute Finland (Luke).

Changes observed in the oral microbiome and inflammatory response

The effects of yard rewilding were also visible in the mouth. In just three months, changes were observed in both the composition and functional properties of the oral microbiota. Functional changes manifested as alterations in metabolic pathways, such as a potential decrease in the L-histidine amino acid degradation pathway. Docent Olli H. Laitinen from Tampere University, who led the biochemical and immunological analyses of the study, states:

“The change related to histidine degradation is connected to amino acid metabolism and the function of the body’s immune system. This may indicate that the diversification of the environmental microbiome affects the function of the oral microbiota and, through that, the interaction between the microbiome and the body.”

Furthermore, higher diversity in the oral microbiome was linked to lower levels of the inflammatory cytokine IL-6 in saliva. Only among the adults whose home yards had been rewilded was the picking of berries and fruits in autumn associated with signaling molecules that regulate immune system function, such as the anti-inflammatory cytokine IL-10.

“Although the study did not look at actual disease outcomes, the findings support the biodiversity hypothesis, which suggests that exposure to biodiversity can promote the normal functioning of the immune system,” Laitinen says.

Amount of deadwood indicates environmental diversity

One of the most intriguing findings of the study relates to decaying deadwood. The more deadwood there was in the participants’ immediate neighborhood, the more certain microbes associated with natural environments were detected on their skin and in their oral microbiome. Deadwood has long been considered an important indicator of biodiversity, as it provides a habitat for a vast array of bacteria, fungi, and other organisms.

“This study brings a new perspective to deadwood, linking it directly to human health: the amount of decaying deadwood in the neighborhood was associated with the composition and function of the human microbiome,” Sinkkonen emphasizes.

The results suggest that the amount of deadwood could serve as an environmental health metric, reflecting not only environmental diversity but also the microbial exposure a human receives and its potential health effects.

“In the future, deadwood could complement metrics based on the amount of green space and plant species richness, which have traditionally been used in environmental health research,” Sinkkonen continues.

Towards healthier urban environments

“The results of the study suggest that urban yards, parks, and other green spaces should be designed to be more natural, leaving room for wild nature. In practice, this means diversifying plant species, using deadwood and wood chip mulches, and ensuring that organic matter is not completely cleared away from the yard but allowed to decompose on site. Such solutions can increase human exposure to environmental microbes,” Sinkkonen and Roslund encourage.

“Longer-term and larger studies are needed to determine how long-lasting the observed changes are and how they affect health in the long run. Even now, the results offer new perspectives on how urban nature can be developed to support the well-being of both humans and the rest of nature. At the same time, they emphasize the importance of natural habitats like deadwood as part of a healthy urban environment,” Roslund concludes.

Study: Roslund et al. (2026) Neighborhood deadwood and yard rewilding modulate commensal microbiomes and inflammatory signals among urbanites, Microbiome. https://link.springer.com/article/10.1186/s40168-026-02413-w

From Tampere University, the research groups of docent of virology Olli Laitinen and professor of urban planning Juho Rajaniemi participated in the study. A scientific article on this joint research by the Natural Resources Institute Finland, the University of Helsinki, and Tampere University was published in the Microbiome journal.

For further information:
Senior Research Fellow Aki Sinkkonen, University of Eastern Finland, aki.sinkkonen@uef.fi , +358 50 572 4875
Senior Research Scientist Marja Roslund, Natural Resources Institute Finland, marja.roslund@luke.fi, +358 29 532 2256
Senior Research Fellow Olli Laitinen, Tampere University, olli.laitinen@tuni.fi, +358 50 342 7273
Postdoctoral Researcher Fellow Laura Uimonen, Tampere University, laura.uimonen@tuni.fi, +358 50 464 9758