Human Ecology - part 4 home stretch!

So where do humans fit into that forest ecosystem? Well, we know humans were first hunter-gatherers. Compared to today’s norms, hunter-gatherers were few and short-lived, in part because food was scarce and difficult to come by.

Enter agriculture. People literally had more food to eat. Remember - in our “natural” forest ecosystem, the cycles of minerals and loops of life were relatively small. Fast-forward to the new global human ecosystem, dependent on agriculture, which moves biological material (food!) long distances to support billions of humans. The whole situation of 6.8 billion of us grew up so fast that the norms of nutrient cycling (and just about everything else) have dramatically shifted.

Take nitrogen, for a start: it’s essential to building proteins in all living creatures. It enters our Cycle of Life when bacteria that live in nodules on the roots of legumes “fix” it – convert it from its inert atmospheric form to a bio-available form. Before the invention of agriculture, the global nitrogen budget was perhaps at equilibrium. But when people discovered we could benefit by planting more legumes, we planted more and more of them, and the annual global rate of nitrogen getting fixed rose accordingly. Humans shot an even bigger dose of nitrogen into the works when we discovered how to fix nitrogen chemically, in factories. Now, we ship bio-available nitrogen all over the world for people to put on crop fields. We’re so focused on getting more nitrogen to our crops that we overdose, and the excess washes downstream.

The species in the “natural” ecosystems, both land and aquatic, aren’t adapted to the new, higher levels of available nitrogen – see algae blooms and dead zones. Basically, the global nitrogen cycle is in flux – a lot is flowing downstream and very little ever makes it back up. This is typical for much of the nutrients that support human life: in “natural” ecosystems nutrients cycle round and round, while in our human ecosystem their path only goes one way.