Neighborhood deadwood and yard rewilding modulate commensal microbiota and inflammatory signals among urbanites

Background

Global ecosystem deprivation is linked to reduced microbial diversity and diminished immunological resilience. Urban rewilding and decomposing plant matter have been suggested to reverse this deprivation and support human health.

Methods

We rewilded 21 urban private yards with vegetation and deadwood. Control yards (15) were analyzed for comparison. We collected microbial samples and used vegetation and deadwood inventories, landcover data and questionnaires to determine the effects of rewilding and living environment on skin and salivary microbiota, gene pathways and cytokine levels (IL-6, IL-10). Samples were collected before the rewilding in summer and three months later in autumn.

Findings

Rewilding preserved skin microbial richness in comparison to control group, including previously health-associated Alpha- and Gammaproteobacteria, despite the normal seasonal decline and less outdoor time in autumn. Deadwood abundance within 200-m radii associated directly to beta diversity of skin microbiota and Gammaproteobacterial taxonomies.

In saliva, deadwood was directly associated with the diversity of functional gene pathways, which in turn was negatively associated with pleiotropic IL-6 levels. Rewilding was associated with a decrease in L-histidine degradation and an increase in Mycobacteriaceae.

Interpretation

Since both yard rewilding and neighborhood deadwood preserved rich commensal microbiota and reduced pro-inflammatory signals, decomposing plant matter, not just plant richness, seems to be crucial for ecosystem services that contribute to health. Since deadwood abundance was associated to reduced pro-inflammatory signals, it may be a suitable indicator of environment supporting immunological resilience.

Our findings provide an incentive for future strategic investments for planetary health.

Funding

Strategic Research council Finland.