The Human Microbiome;
The Foundation of our Health
& The Role of Forests Building Diversity
Introduction to Biodiversity
Biodiversity refers to “the variety of life on Earth, in all its forms, from genes and bacteria to entire ecosystems such as forests or coral reefs”. It is the result of 4.5 billion years of evolution, where humans actively play a role (UN, 2023). Biodiversity builds a web of life that forms the basis from which we depend on for many things (food, water, medicine, stable climate, economic growth, etc.). For this reason, over half of the global GDP depends on nature (World Bank, 2021) and more than 1 million people rely on forests for their livelihoods (UN, 2011).
The human microbiome is a highly diverse community of bacteria, virus and yeasts present in our stomach, mucosa and skin, and is also part of the biological diversity on earth. It makes up to 1kg of our body weight and it is responsible for more than 20.000 functions in our body (Verdaguer, 2022). If we lose them, we lose the foundation of our health (FAO, 2020). Recent studies suggest that an ecological perspective is important to understand microbial impairments and dysbiosis, and related diseases that occur nowadays in urban environments and in lifestyles with low levels of interconnectedness with nature (Prescott et al. 2017).
The human microbiome present in mouth, skin and gut is a community of bacteria living in our bodies which is also part of the biodiversity of the world. In the following lines we explore how establishing a contact with nature, and more specifically forests, impacts the diversity present in the human microbiome.
Humans and Forest Microbiomes
Today we know that there is certain microbiota associated with certain habitats playing relevant roles in the whole ecosystem functioning (Baldrian, 2017). The microbiota refers to the inseparable functional unit or community of microorganisms where pathogens represent only a tiny fraction (Berg et al. 2020). The concept of human microbiome (considered by scientists our “last organ” Berg et al. 2020) was one of the first to emerge, and recently other microbiomes –of plants, waters, soils, atmosphere, and forests– have been the focus in several research fields (Baldrian, 2017). Yet, the human microbiome, the trillions of microbes that co-evolved with humans inhabiting our bodies creating complex, body-specific and adaptive habitats (Lloyd-Price et al. 2016), is today in danger. Evidence shows that Western lifestyles has lead to a loss of microbial diversity and function, as well as the extinction of important beneficial microbe lineages that offer space for expansion for opportunistic pathogens (Berding et al. 2021).
While today most studies focus on the role of diets as key factor shaping the gut microbiota, other factors such as environmental exposures, cultural preferences, and stress also have significant influences (Lynch & Pedersen, 2016). Current rapid urbanisation and the abuse of chemicals in food systems are associated with reduced microbial diversity, leading to maladaptation and impaired resistance to pathogens (Gordon et al. 2017), and associated with an increased risk of immune and metabolic diseases (Smits et al. 2017; Domingo-Bello et al, 2018). Recent studies in endangered primates have shown that habitat degradation caused by anthropogenic disturbances negatively influences the microbial diversity of the primates (Barelli et al. 2015).
By contrast, forest-based communities, such as Indigenous communities with seminomadic lifestyles in mountainous territories that have no documented previous contact to Western culture, have shown an unprecedented high bacterial and functional diversity in their microbiome (Clemente et al, 2015). The Hadza hunter-gatherer tribe of the East Africa Rift Valley offer an insight and a profound appreciation of the flexibility and co-adaptive capacity of the gut ecosystem (Schnorr, 2015). Also, rural farming communities in Burkina Faso, Malawi and South Africa show higher microbial diversity to that found in industrial groups (Schnorr, 2015). People living near forest and agricultural environments show higher beneficial bacteria (Prescott et al. 2017). Even in urban environments, the closeness to green spaces and biodiverse vegetation is an important determinant of bacteria diversity in the human microbiome (Flies et al. 2017; Prescott et al. 2017)
The forest microbiome consists of various forest habitats: the foliage, the living trees wood, the bark surface, ground vegetation, rhizosphere and roots, litter, soil, deadwood, rock surfaces, invertebrates, wetlands and atmosphere – all of them inhabited by fungi, bacteria and archaea (Baldrian, 2017) (Figure 1). Primary water, soils and forests habitats are recognised as significant natural reserves of antibiotic resistance (Vaz-Moreira et al. 2014). Many processes in the forest depend on the activity of microorganisms, such as litter decomposition, carbon fixation and nutrient uptake of plants (Morera et al. 2022).
Humans beings are also depend on the primary forest microbiome for the good functioning of the the body and mind. This is what the new science on "Forest Bathing", an original tradition from Japan, has proved. Yet, sometimes we do not need science to tell us what is good for us; we all know how good it does to spend a day in nature or to swim in the sea. Now science is also showing what is invisible to our eyes at first sight, but that we feel already.
Future Perspectives
The latest science says that the microbiota–gut–brain is in constant communication (Berding et al. 2021) and Nature-Based Health Intervention is now the new prescription for physical and mental health (Flies et al. 2017; Nabhan et al. 2020). Given the current situation of diversity loss in human microbiomes in urbanised Western societies, it is of high relevance to find new ways to promote a biodiverse and healthy human microbiome. Nature-based solutions that have received attention in the last years are urban forests, green and blue spaces, the famous Japanese forest bathing, regenerative agroforestry or care farming/gardening as a therapy for health recovery (Aerts et al. 2018).
The Tiny Forests Association (miya-forest.de) founded at the HNE is particularly interesting for this purpose, as it creates climate-resilient mini-forest patches in school garden for children to come into contact with the beneficial environment provided by soils, plants, trees and flower, that diversifies their microbiota. Recent studies demonstrate that outdoor activities in nature increases beneficial bacteria and serotonin levels in preschool children (Sobko et al. 2020). So, who does not want their children to be happier?
Now it is time to plant tiny forests in school gardens, to green cities again and to establish back a connectedness to the forest microbiome, that will ensure our microbiome diversity, our physical and mental health, and our future capacity as a specie to co-evolve in this world.
Literature
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