Tuesday, January 29, 2013

Use diversity to get more from your forest!

We need all our parts!

In our race to be the fittest species of all time, we humans have perfected the art of manipulating natural systems, often simplifying them down to a single species (think corn, pine, rice, oranges, cows, salmon).

Single-species systems don't really exist naturally - even Antarctica, which is 99% covered by permanent ice and snow, has over 450 plant species and around 200 species of invertebrates crawling around there as well. Add to these all the plankton, fish, seabirds, penguins, seals, and whales that live off the coast and you have a diverse and active place.

Gentoo penguins add to Antarctica's biodiversity
photo: PaoMic, Wikicommons

Obviously, the simplification perpetuated by human activity downgrades the fitness of all those other species that no longer live in these places (these places being 50% of Earth's ice-free land area!).

But, as we learned in a previous post, ecological systems are typically complicated and interconnected, and, like other systems, need all their parts to work properly.

photo: Funny pics
---Think about your skeletal system: it needs bones to support you, cartilage to move joints, tendons to connect bones to muscles so you can move, and teeth to chew food!

---Or about your home's heating system (needs an energy source (e.g. gas, electricity), a furnace to warm the air, a distribution mechanism (pump, ducts, etc), and a control to regulate it (e.g., thermostat).

A sprained ankle or broken collar bone sends you to the doctor, and a broken heating system sends you to the repair shop. It's the same for ecological systems (OK, there's no repair shop, just time) - they need their various parts.

By helping to maintain functioning systems, the diverse nature of living things (biological diversity) maintains our collective global fitness.

Yes, I know, people live very nicely, thank you, surrounded by cows, sheep, and chickens or rats, pigeons, and squirrels, right? But the resources used by people on farms and in cities require products or processes from forests, oceans, grasslands or other natural systems in other places.

Healthy and wealthy

Two recent scientific studies of plantation forests give simple yet concrete examples of this. Apparently, having more tree species makes us both healthier and wealthier.

By wealth, I mean the natural capital or "biowealth," a term coined by Cary Bradshaw at ConservationBytes.com. These concepts refer to the services (e.g. producing soil, wood, and other products; maintaining the flow of nutrients in soil and plants, pollinating & dispersing seeds of crops, storing carbon, and filtering water) provided by natural systems that we use every day and that would be incredibly costly to try to reproduce artificially.

diverse riparian forest in Peru
The authors of the first study compiled data from 54 local studies and found that stands with more trees species, especially when they occurred at more even densities, produced up to 24% more wood than single-species stands.

A more recent study in northern Europe found that production (plantation) forests with more tree species produced more wood (aka "tree biomass), game, and berries, and stored more soil carbon than those with fewer species. Moreover, different tree species provided different quantities of the various services.

diverse forests in Sweden
photo: Peter Turander Azote
Similarly higher biomass production, long-term survival, and service provision have been found in grassland ecosystems studies with greater and fewer numbers of species.

Why would this be? Why are these studies finding greater productivity in stands with more species? Isn't is more efficient to plant one species and provide it with its ideal conditions (shade/sun, soil chemistry, etc)? Apparently not.

So...why is diversity important for fitness?

Larger numbers of species may reduce the temporal variability in ecosystem processes; that is, services such as berry production or supporting game animals might be provided best by different tree species at different times of the year. This improves the fitness of the animals or us, the ultimate consumers, but what about the trees themselves?

In fact, the fitness (survival + reproduction) of a species with individuals that are surrounded by those of other tree species may be improved by improved suppression of disease.

Monoculture with canker disease
photo: California Dept. of Forestry & Fire Protection
Unlike in a natural forest or prairie, in a monoculture (1 species), the plants of a single species are all together.

Insects and pathogens that specialize on the crop of interest can spread quickly from plant to plant (thus the ubiquitous use of pesticides), whereas rotating crops and intermixing several species of plants lessens bugs' ability to establish themselves and damage the plants.

In addition, interactions between different tree species may also encourage particular microbiotic communities that lend higher resistance to plants against pathogens or insect predators.

So, more trees ==> more wood, more critters, more berries, more other plants ==> more trees!


  1. nice and informative post thanks for sharing it i really like it.

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