Our biogeoclimatic monomyth

Published on 2024-02-25

As a bit of jargon, you've probably heard of the word "biome" before. A biome is a major regional complex of similar life. The biome I live in would probably best be described as a taiga, or a boreal forest: heavily forested, mostly by pines, spruces and things of that nature.

My home isn't the only boreal forest in the world. In fact, if you looked at a map you'd notice that there's a strip that traverses the whole circumference of the Earth that's mostly boreal forests along the more polar latitudes of the northern hemisphere. But, the boreal forests of North American aren't the same as those of Russia or Finland. They are similar in certain regards, but different. They've got different organisms living in them that respond well to the same kind of climate, and that's ultimately what a biome is: a set of climatic conditions you might find in different parts of the world. Those different places will lend themselves well to similar organisms.

We have a few ways to taxonomize the different, particular, large-scale environmental communities around the world; biomes are probably the most abstract. We've got biogeographic realms (e.g. Nearctic, containing most of North America), bioregions (i.e. Cascadia, also known as the Pacific North West, including lots of British Columbia, Washington State and Oregon), and below that we have the relatively small but still fairly big ecoregions, characterized by a relatively distinct set of organisms that inhabit it.

Does this really matter? I don't know. I don't really like taxonomy. I'm a lot more interested in how the boreal forests of Cascadia are similar to those of Siberia, rather than how they're different. But I do think it's useful to understand for what I'm about to say.

In British Columbia, the government maintains a fairly nuanced system for identifying its many ecoregions, called the Biogeoclimatic ecosystem classification system. There's a whole bunch of them. They're identified by fun little acronyms. For example, at the bottom of many valleys in the interior, you'd find the BG zone, where BG stands for bunch grass.

Bunch grass is... just that. A bunch of grass. They grow in bunches or tufts. The BG zone isn't "defined" by the presence of bunch grass; you can find it elsewhere too. The BG zone is defined by a number of factors, including the regional climate, soil, flow of energy, and so on. And still, we don't call it "the southern, low-elevation, relatively and consistently warm and dry zone," we call it BG.

Bunch grass gets to take the name of the BG zone because bunch grass is what we might call a "climax species" for this particular ecoregion.

Climax theory is this idea that ecosystems have a perfect, ideal state. Following a catastrophic disruption, let's imagine that all species of a particular ecosystem are killed, and the land is returned to a fertile yet empty state. Slowly, species will return. First, small species that really like sunlight will show up--these are called "pioneer species." Then, some taller species, perhaps, will start to crowd them out--what we'd call "serial species." Finally, any new species that grow need to be able to tolerate a certain amount of shade. These species will grow under the canopy of the older ones, eventually outpacing them, and becoming what we'd call the "climax species." Once an ecosystem is dominated by climax species, it becomes a climax community. In the case of forests, we'd call this old growth.

God hates old growth

This is not "necessarily" true--lots of weird things happen in nature all the time, but this is a pattern we see happening a lot.

Climax theory suggests that because a particular place has a particular set of environmental conditions (climate, soil moisture, soil composition, hydrology, etc.), that particular place has a particular, "ideal" climax community that it'll always be trying to reproduce following a catastrophic disturbance, and that we can infer what that climax community is based on those conditions.

Higher in the mountains, you might find the MS zone: an ecoregion of densely packed trees, named for montane spruce. Only, you're unlikely to find much spruce there. The climax species of the MS zone take hundreds of years to fully mature, and due to the ecoregion's density, they tend to be extremely susceptible to fires that wipe out the whole stand. Instead, you'll likely find a mixture of other "serial" species. Our imagined, ideal state of the MS zone isn't what we find exists in practice.

Climax theory is widely seen as untrue today. The truth is, following a disturbance, anything could happen. Maybe the old growth will come back, or maybe it'll be replaced by something totally new. It's not unlikely the replacement ecosystem will be similar to the old one assuming the environmental conditions haven't changed, but it won't necessarily be the same. We've seen it happen before.

And still, the ideas behind climax theory seem to seep into our discussions of ecology all the time.

Is framing ecosystems in terms of their climax species a bad idea? Maybe. It'd probably make more sense to put more of an emphasis on what exactly makes that "climax species" so important at the ecosystem's maturity (or rather, that particular "stage" in the ecosystem's development--the one we place so much value on). But we know that spruce is just waiting to outgrow its Douglas fir neighbours in the MS zone. At least, that's how we feel. If only it wasn't for those wildfires. In knowing that a particular species is likely to grow when the ecosystem reaches maturity, it feels as though the ecosystem begs to be characterized by it.

In other words, there's a certain allure to the idea of climax communities, even if we know they aren't literally real. They suggest that the natural world has a direction--a purpose. Something to work towards.

They suggest that nature is a bit like us. Or at least, how we want to be.

The cyclical structure presented by climax theory, through its growth, climax, disturbance and regeneration, reminds me a bit of the monomyth. At least, it feels a lot like the stories we've been telling about ourselves since time immemorial. It's not all that surprising, then, that'd it be the story we tell about ecology, too. We like to read ourselves into things.

There is a certain value to the whole cycle, whether or not the "climax" stage is as definite as those who first conceived it may have wanted to believe. Having an appreciation for it, respecting the process, has its advantage. Climax communities are similar because they are well suited for the particular environmental conditions of a region. What we might call anthropogenic communities--ecoregions that are the way they are because people wanted them that way, remain stable as long as we keep sustaining them. Us not actively satisfying their needs constitutes a disturbance unto itself.

In the past, few people took the BG zone very seriously, as is the case of grassland throughout Canada. Grassland is easy to build on. We turn it into agricultural land. We build cities on it. Today, when I visit the city and I look around, I see lots of species that probably wouldn't be here if it wasn't for our active intervention. There isn't many BG zones left in the province--they're starting to be considered endangered because of these interventions.

There's not many species this particular set of environmental conditions can support; there's a reason we treat its grass as a climax community. Were we to leave it be, it's unlikely the already lacklustre biodiversity we've introduced would stay on its own, but following a disturbance like this, it's impossible to say if its characteristic bunch grass would ever return.

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