Urban Nature

diversity in the garden

Why should you cultivate dandelions in sidewalk cracks, spiders in the attic and mushrooms in lawns...

Now that spring has fully arrived, I’m spending time weeding my garden. Volunteer plants have sprung up everywhere, like, well, weeds. I’m not pulling everything out - much to the annoyance of my neighbor who claims my few dandelions are an eyesore even though millions are in the park across the street.

Even in an urban environment (like where I live), we’re still part of nature. Urban living doesn't have to mean surrounding ourselves with a concrete jungle; we can still make room for diversity in nature. Even the dandelion that takes root in a tiny crack in the pavement and the moss that grows on your roof counts as diversity.

Diversity is important because it adds a complexity that makes an ecosystem stable. A single change that destroys one species is not a big deal if many species fill that niche, but a very big deal if it was the only species. For this reason, any ecosystem with only a few species is vulnerable. Consider a lawn containing a single species of grass - soon weeds will move in or nutrients will be used up, forcing the owner to take drastic action like applying herbicides or fancy synthetic fertilizers. Or, consider diversity in relation to our food crops: using a single variety can result in crop failures and no back-up to turn to. A sad example is the potato famine that occurred in Ireland between 1845-1852 (from wikipedia article here). Even though there are many varieties of potatoes on this planet, the Irish only planted a select few species and blight wiped them out - bad, bad news.

A diverse ecosystem, in contrast, acts to buffer the effects of change. No one goes out into an old growth forest and sprays the dandelions (although, exotic plants can still invade). My garden, which I pack full off as many different crops into my tiny yard as I can, will always produce me something.

Taken as a whole, the Earth is an example of a diverse ecosystem and can be considered a biosphere. People have dabbled in creating artificial biospheres since at least Victorian times. On a small scale, you can go out and buy an 'ecosphere' which is a sealed glass ball filled with water. Inside the sphere is a little ecosystem consisting of shrimp, algae and bacteria, which isn’t very diverse. In 1986, Carl Sagan wrote a glowing article about these ecospheres called, 'The world that came in the mail'. Their makers say these glass worlds can last up to 10 years, but critics say the shrimp are slowly being poisoned by their own waste while starving. Perhaps a bigger biosphere is needed.

Biosphere 2 (earth is Biosphere 1) is a 3.14 acre sealed greenhouse in Arizona that is broken up into several different types of ecosystems. Each ecosystem included several species that filled the same ecological niche, and soils were seeded with micro-organisms in an effort to enhance diversity. In the early 90's, an experiment was conducted by sealing in eight volunteers to simulate using a biosphere for space colonization. I remember seeing the ad for volunteers and being fascinated with the idea; however I had other commitments at the time and couldn't apply - which is perhaps for the better.

These eight people to be were sealed into Biosphere 2 for two years where they grew their own food. Their atmosphere was also enclosed, so the only oxygen available came from the plants within the biosphere. It turns out the biosphere wasn't a stable system: carbon dioxide levels fluctuated widely and oxygen levels couldn't be maintained. All the pollinating insects died, while cockroach and ant populations overran the place. The people sealed inside couldn't grow enough produce, forcing them onto calorie restricted diets.

One result of this experiment was to demonstrate that creating a stable biosphere is currently outside our capabilities. Since we haven’t successfully made a new biosphere, Biosphere I is all we have. So don't get rid of all the diversity that pops up or moves in. Keep a little diversity at home.