I started thinking about this today while listening to the 22nd of April 2007 Naked Scientist Podcast.
Plants compete for resources, and natural systems are very complex with competition going on on all kinds of levels at the same time. When we add fertilizers, ecological niches are obliterated, there’s no competition in those areas, and there’s a loss of diversity. This is discussed in the article “Grassland species loss resulting from reduced niche dimension,” (Stan Harpole in Nature 446, 791-793 Apr 2007). Essentially when one limiting resource is removed, the ecosystem makeup can potentially be changed, or maybe absorb that change and remain diverse. When two or more limiting resources are changed (so let’s say water and nitrogen), then the whole balance is thrown. What i mean here by limiting is that these are things that were, naturally scarce. Species develop ways to try and get scarce resources or make up for them being scarce. When I say that a limiting resource is removed, what i mean is it is no longer a limit. The resource is plentiful, so there’s no challenge in trying to get it.
Essentially when a large quantity of a nutrient is flooded into a system (as happens with fertilizers), the species best suited to that niche (which is overriding all the other more subtle niches) takes over. One species becomes totally dominant and diversity is lost. In the grasslands experiments performed this only took two years to happen. Based on ongoing research in England, the restoration for these systems to restore diversity can take 150 years or more, if restoration is even possible.
Fertilizer doesn’t stay put, that’s why we apply them all the time. They tend to either move into the air, or move into water. One of the best examples is dead zones around various coastal areas where nitrogen runoff causes huge algal blooms, the algae that lives there isn’t always photosynthesizing. When conditions are unfavorable they consume oxygen available in the water, leaving less for things like fish, and the decomposition of algae that dies when the nutrients run out also requires large amounts of oxygen. Essentially these intense runoff zones are biologically dead. Nothing can make it there because the nutrient balance change caused a mass increase in one species that then consumes resources that other life would need to survive. This isn’t unique to one specific region, this is a problem that plagues agricultural development everywhere. What’s interesting to me about this stuff is the observation of recovery.
Harpole notes in his interview that one of the biggest areas of influence on the human part is Nitrogen. This doesn’t get big press most of the time because nitrogen isn’t one of the concerns in climate change or any of the other sexy news-science stories, but this is a big deal. Humans contribute about as much nitrogen to the world’s ecosystems as natural processes do. That enormous impact greatly modifies natural systems, usually in a way that dumbs down diversity. The one thing about diversity is that it makes a system robust and better able to cope with disaster. If you reduce a mass plot of land to one plant species that thrives on high nitrogen, but it can’t come back from something like fire, or warmer temperatures, or flood, then when those kinds of natural “disasters” (I prefer “fluctuations”) hit, you are screwed. No wheat or corn or rice for you, and sadly, not much of anything else either because you’ve wiped out that plot of land and often created dead zones out of whatever’s downstream. Not only that, the land usually becomes pretty crappy at generating its own Nitrogen when people take over the process.
It’s just like the problems we see with outsourcing. If worker A makes shirts cheaper than worker B, then I am going to rely on worker A. Worker B is, in a free market system, going to either move somewhere else, go on welfare, or get a different job. If you outsource enough of your work force, whole companies shut down, and in some places in the US you end up with depressed struggling ghost towns. Natural systems are the same way. If you change the system, some species will move (this happens with freely moving things like critters). Plants generally don’t get those kinds of benefits, so they wither up and die. If enough of the ecological community either moves or dies, the system is about as healthy as any low income community. Think of the investment it takes to recover a city in distress. We don’t even do THAT well, we normally just push poor communities somewhere else. We do the same thing trying to repopulate natural dead zones, it takes a huge investment of resources, time, labor, nutrients, and species to get things running, and even at that, it may require close management forever, or at least a length of time expanding beyond a human lifetime.