Rewilding is the concept of reintroducing native animals and plants to an area where they have declined or gone extinct.
One of the most successful, but also controversial, rewilding programs was the reintroduction of wolves into Yellowstone National Park. Whilst some local sheep farmers and residents didn’t necessarily appreciate having these roving predators on their doorstep, the ecosystems of Yellowstone have seen a dramatic recovery since wolves were reintroduced. The ecosystem recovery started with a control of elk populations, which led to a recovery in willow tree populations, and with it beaver populations, who require willows to over-winter.
One of the most successful, but also controversial, rewilding programs was the reintroduction of wolves into Yellowstone National Park. Whilst some local sheep farmers and residents didn’t necessarily appreciate having these roving predators on their doorstep, the ecosystems of Yellowstone have seen a dramatic recovery since wolves were reintroduced. Most notably in the control of elk populations, which has led to a recovery in willow tree populations, and with it beaver populations, who require willow to over winter.
The rewilding concept has also been applied to cities. Edmonton in Canada has developed a range of wildlife passages, now 27 in total, that reconnect patches of native habitat, enabling the safe movement of animals of all sizes across the city. Rather than being an afterthought, the project now deliberately accommodates wildlife movements into the design of city infrastructure.
Bringing nature back into cities is a growing trend across the world. Another group, Rewilding Britain, is focused on re-creating habitat and reintroducing species such as boar, lynx and bluefin tuna across the UK. Rooftop gardens in the middle of cities have also been used as locations for conservation plantings of endangered grasses and plants in the City of Melbourne (see a previous blog on the topic).
Whilst urban rewilding is clearly good for plants and animals, it can also be good for people. Being in and around nature has a known positive effect on our mood, reduces our stress hormone levels and can even boost our immune system. A program promoting this nature exposure is the Biophilic Cities Project, a network of communities that seeks to create a better connection between people and nature through urban design.
“… if you live in and around green space and biodiverse habitats the health benefits in terms of lowered incidence of respiratory disease can be dramatic.”
It’s easy to understand the positive and calming feelings we get when we are exposed to nature, but we still don’t fully understand the reasons behind the physical benefits.
Some recent ideas put the benefits down to the re-exposure to ‘old friends’, a set of commensal or positively associating bacteria that we have evolved alongside for millions of years, but today fail to interact with due to our increasingly urbanized lifestyles. Having new opportunities to be exposed to this environmental microbiome, then influences our microbiome and challenges our immune system in positive ways.
So how do we reintroduce the positive microbiome back into our lives?
Well if there has been a decline in the natural microbiome and our exposure to it due to urbanisation, then restoring native plants and animals back into urban contexts should allow the microbiome to return, and along with it restore its positive health outcomes.
This is the basis of the microbiome rewilding hypothesis as proposed in our recently published paper. Several lines of evidence indicate that this hypothesis has an excellent foundational basis.
The first line of evidence is a study of the environmental microbiome of old pastures that have undergone restoration planting with trees. At these pasture sites, in addition to a return of floral biodiversity and soil health, planting trees resulted in a dramatic recovery and return to the native microbiome in only 8 years (also see a previous blog). Despite these sites having a long and dramatically altered land use history (i.e. >100 years of grazing), biodiverse plantings had a strong positive influence on the soil bacterial community.
Interestingly some microbial groups showed particularly strong patterns of change. For example, Acidobacteria increased with restoration age. This trend is supported by previous work that found Acidobacteria are more abundant in forest and grassland soils rather than degraded soils, and have been used as a functional indicator of the health of soils. Conversely, the Firmicutes group of bacteria declined in abundance with restoration age. Firmicutes include the Clostridium group and other well-known human pathogens. This observation indicates that restoration of biodiverse vegetation communities can also link to improved human health outcomes.
The second piece of evidence is a correlative study undertaken for Australia that found that living in the vicinity of biodiverse habitats was strongly associated with lowered incidence of respiratory disease, and that the quality of green space appears to be important in achieving health benefits. Indeed the effect of landscape biodiversity ranked highly among other known correlates of respiratory health, both positive (socioeconomic status) and negative (smoking, obesity).
Put these two pieces of evidence together and there is then a significant imperative to start engineering our urban cityscapes to introduce many more green spaces, populated by a range of native plants and their microbiome, as a preventative health intervention.
This approach to engineering native habitat has also been promoted recently to help boost populations of native pollinators and improve pollination services in and around pollination-dependent crops.