Week 5: Human impact

Understanding ecosystems is all about understanding the interactions that are going on within each system. Looking at the types of interaction helps us to set up a system's boundaries. The transfer of energy and nutrients within the system helps us understand how it works. Key to this is measuring what happens to be energy that enters the system from the sun. The total energy trapped by photosynthesis in an ecosystem is called the gross primary production. The energy left after some has been used to maintain the plants themselves is called the net primary production. And that is key. The more net production an ecosystem has, the more energy there is available for transfer within the system. So what happens if the amount of net production changes? And what could make that happen? Yes, you guessed it. Like it or not, we have an impact on our environment and in turn, affect carefully balanced ecosystems around the world. Humans aren't the only factor, but it's worth looking at the effect we're having. In 1975, it was estimated there was approximately 2,450 million hectares of rainforest on the planet divided between Africa, Asia, and South America. In 1997, satellite data shows there's 1,116 million hectares of rainforest. That's a fall of 50% in just 22 years. And most of that loss is due to human activity.

The problem with unintended consequences are they're unintended and unforeseen. And while you could be manipulating a system like a rainforest by taking away the vegetation, what's quite clear is that you're removing habitat. What perhaps isn't so clear is that you can have knock on effects on its climate in the long term.

These knock on effects could be very small. But even tiny changes can be significant. Just how significant depends on what happens to the lost rainforest. Some ecosystems are more secure than others. They hold a better hand, as it were. But a few bad cards, and a rainforest system could quickly change. If the land is farmed, the ecosystem will change dramatically. When many trees are felled, rainforest can turn quickly into grassland. But even subtle influences over a longer time period can have a big effect.

If you have lots of species from an ecosystem, you really don't know what the effects will be. In some respects, we're going through a natural experiment right now where we're losing species. So by tracking what's going on in the Earth's ecosystems, we might be able to get a handle on this. An alternative approach is to actually set up our own experiments to investigate this question.

So humans do have an effect. And it can be significant. But it all depends on which part of the system is being affected by human activity. Take that most civilised of human activities - international air travel. Imagine that this luxury airliner is an ecosystem. For that first class experience, every bit of the plane is vital. But if we stopped serving free champagne, it would still fly. Take away the peanuts and the in flight movie, and it's still airborne. It'll even fly if one of its engines is on the blink. But there's a limit to how much we can remove before it all goes wrong. And we can think of ecosystems in exactly the same way. Some elements are crucial. But are there some additional extras the system could survive without? One system that's pretty much everything included is the system of pollination. But we could argue that we could do without the personal touch the bees provide. Many species are pollinated in other ways. And in truth, we don't know what would happen if we took bees out of the equation. Let's take another example - peat bogs.

If you start chipping away at an individual component of an ecosystem, you can have all sorts of unintended consequences. Now, one good example could be an upland peat bog. These humble ecosystems actually have been mined for years for their carbon. It's a form of fossil fuel. So in mining this apparently abiotic component of the system, there are consequences to that action, because this peat bog actually functions as a great big sponge. So when you have large rainfall events, that big sponge soaks up the rainfall, and it prevents that rainfall from disappearing down the rivers too fast. So you remove that sponge all of a sudden, you'll get flashier, more intense flooding events.

So ecosystems are not fixed. They're carefully balanced, fragile, and subject to change, through natural disturbance and through human impact.