The double-edged sword of diversity

We live in a very unique microclimate at Meadowcreek.  It’s always cooler than any place around us because our narrow valley runs north and south.  Dusk and dawn last a long time because the sun has to get over the Eastern ridge in the morning and disappears early over the Western ridge in the evening.  Meadowcreek valley is also unique due to our many springs.  These keep the valley moist all year.  Being cool and moist, we often get fog in the morning which fills up the valley while above the valley are clear skies.  Or sometimes the reverse.

eat and be eatenThese conditions have created mushroom heaven at Meadowcreek.  We have so many unique species, the mycologists have an annual meeting here.

Mushrooms and their family, the fungi, have a long and glorious history on the planet.  They have much to tell us about both the importance and the perils of diversity.

You know about the asteroid that destroyed the majority of life on the planet, wiping out the dinosaurs and much of the plant life of the time. In the wake of the impact, light from the sun hardly penetrated the layers of ash and debris held in the atmosphere. The only life forms most capable of handling such a unique challenge were mushrooms and other fungi . Before the atmosphere cleared and the dust settled, the fungi continued to decompose dead plants, clearing the way for seed ferns that survived in the soils below. What would have become of the surface of the planet without the fungi covering the surface, perpetuating the decay of plant matter?

So fungi saved the planet after the Cretaceous-Tertiary extinction.  But fungi need plants to survive.  Though the mushrooms can survive without direct sun, they need continual plant decay and the sugars produced. The work of mushrooms then creates soil components which allows more plants to thrive.

This shows the complementary diversity of all resilient systems.  Each component eats and is eaten in turn.  Food we eat and food we become. Selfish or non-complementary systems die, and usually die young, because they don’t realize that giving builds up the system which can then provide the inputs it needs. Whenever a selfish species arises, its lifecycle eventually decays because it destroys the system supporting it.  The earth is now experiencing a mega-extinction event because we have one selfish species, man.

Man, in his industrial hubris, has created the concept and reality of waste.  There is no waste in resilient systems.  In resilient systems, everything is consumed and transformed into alternate materials for alternate uses. It is this recycling process that manages to construct huge redwood trees with solar energy and soil minerals as the only external output. How does a forest manage to build such great structures with seemingly so little input, particularly when we consider the vast inputs required for modern agriculture?

The redwoods and all forests require a vast army of fungi, bacteria and other soil organisms to recycle nutrients so they are available to the trees.  The soil organisms are just trying to survive and reproduce, not supply nutrients to the trees.  But they are so complementary to the trees that their output (degraded plant matter) is the crucial input (nutrients) for the trees.

It’s those sort of complementary systems that keep you and your systems thriving and prospering even in the wake of a metaphorical asteroid. Stable ecosystems such as a tract of mature oak hickory forest are often see as sustainable, lasting or self-managing. These forests are in fact in the K phase, having converted and stored nutrients into trees, and have low and decreasing diversity. A contiguous tract of mature forest has much less diversity than a patchy landscape composed of dense woods and meadows, shrubby areas and young trees. These patchy landscapes provide habitat for animals and plants at every stage of forest succession from new growth after a forest fire to long standing trees that harbor particular species. Traditional forest management tends to produce more homogeneous growth than those forests disturbed naturally and increases the likelihood of unexpected catastrophic change.

Many see the high diversity of resilient systems and conclude that increasing diversity will increase resilience. In fact, the opposite is often true over the long term.

In today’s modern societies diversity is about inclusion. In ecosystems, resilience requires exclusion as well.  More diversity is not always good. Increasing diversity by adding new species to an existing ecosystem can destroy multiple species and thus reduce diversity. Species which don’t complement existing life can destroy systems where they are introduced.

When the rabbit was introduced in Australia it certainly increased diversity of species—momentarily. Then, because there were no natural predators for rabbits, they began to expand exponentially. Rabbits are very good at finding the seedlings of shrubs when they are very small and grazing them out to the extent where the native shrubs are completely unable to regenerate. Rabbits also threaten some of the native burrowing animals, such as the bilby and the burrowing bettong, by moving into their existing burrows and competing for food. Rabbits are responsible for serious erosion problems, as they eat native plants, leaving the topsoil exposed and vulnerable to sheet, gully, and wind erosion.

When the Asian chestnut blight fungus virtually eliminated American chestnut from over 180 million acres of eastern United States forests in the first half of the 20th century, it was a disaster for many animals that were highly adapted to live in forests dominated by this tree species. For example, ten moth species that could live only on chestnut trees became extinct.

Aquatic plants such as South American water hyacinth now in Texas and Louisiana and marine algae such as Australian Caulerpa in the Mediterranean Sea have decreased diversity in vast areas by replacing formerly dominant native plants.

Other examples of increased diversity leading to decreased diversity:

1. Man migrated to North America and wiped out megafauna, after he had done the same in Eurasia.

2. The predatory brown tree snake, introduced in cargo from the Admiralty Islands, has eliminated ten of the eleven native bird species from the forests of Guam.

3. The Nile perch, a voracious predator introduced to Lake Victoria as a food fish, has already extinguished over one hundred species of native cichlid fish there.

4. The sea lamprey reached the Great Lakes through a series of canals and, in combination with overfishing, led to the extinction of three endemic fishes.

5. The first sailors to land on the remote Atlantic island of St. Helena in the 16th century introduced goats, which quickly extinguished over half the endemic plant species.

Of all 1,880 imperiled species in the United States, 49% are endangered because of introduced species alone or because of their impact combined with other forces.

This downside of diversity occurs in human social systems. The largest study ever on civic engagement in America, found that virtually all measures of civic health are lower in more diverse settings. In business and government, promoting diversity for the sake of diversity can backfire, breaking down the communication channels and the organization’s ability to build trust or a sense of close bonding within members or associates.  Societies and communities lacking racial diversity are often far more productive and cohesive.

Diversity is a double-edged sword.  More diverse systems are more resilient.  But watch out when introducing diversity into a system.  Noncomplementary diversity will destroy resilience of the system.

For more on diversity in resilient systems and links to all the research cited above, see the diversity chapter of our book on resilience here.  

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