I am not a botanist. I have not done a ton of research into botany. Do not use this article as a primary research tool.

Every week-day I twice pass a lovely new playground that the City of Burnaby has constructed next to a well-preserved region of wetlands. The soil here is wet (duh) and fecund. Animals thrive here. Obviously the first priority of the city is to prevent that from happening in the playground. I make no moral or ethical judgment here, it’s just true: no one wants their kids playing in a swamp and the residents want a place right here that kids can play. Ergo, it cannot be a swamp. Swamps want to make more swamp, and so you need to defend your playground against the constant encroachment of the swamp and do so without killing the swamp, because the swamp is mandated by provincial or federal law. I don’t know which.

So you build a nice sterile gravel path at least a meter and a half deep between the swamp and the playground. You don’t want a sterile playground — in fact you are going to surround it with lush lawn-quality grass — but you do need a defensive perimeter. Okay then — maintaining this perimeter is now priority one.

No problem there. The city is doing a fine job of maintaining this perimeter. There is no danger of the swamp encroaching on the grass. There are two reasons for this: first, the sterile path idea actually works; and second, they managed to kill the soil under the grass.

I’m pretty sure this is how lawn grass and lawns in general work: you regularly cut some bog-standard (aware of the pun, thank you, and there will be more) grass. This is not an aesthetic thing you do. This is part of the control you need to exert over the whole growth culture of grass. What you are doing is preventing the grass from reproducing sexually. I know, put that way it sounds cruel, but it’s true. Because grass grows two ways and one is intrinsically cooperative while the other is intrinsically competitive.

When grass is prevented from seeding, it reproduces asexually, which is not as fun and makes lawns. Because the grass is regularly cut, there is no competitive growth (it’s all mostly the same length and it’s all short so sunlight is equally available and equally consumed). New grass is budded from the existing grass from at or below the soil line, creating a nice spongy mass that holds the dirt together and is very efficient at trapping water and transmitting nutrients. The grass is happy. It’s hard for alien plants to get a foothold in a good lawn, because this lawn is so good at what it does (and the regular cutting is bad news for anything that doesn’t also reproduce while really short). When you cut grass you are literally leveling the playing field, and grass wins this because it is a powerful cooperator when denied sex.

The City of Burnaby did not regularly cut this grass.

More to the point, they let it go to seed and then cut it.

When grass starts to get longer, a marked difference in the amount of sunlight any given blade receives can be had by increasing height.  Increasingly long neighbours strangle out the light for shorter neighbours, and they die. This results in clumping — now the most efficient way to get light is for clusters of tall grass to climb as high as they can (for two reasons, actually) which creates rings of shade around the best competitors. In these rings of shade, very little grows. If it’s dry (and it is) the soil will become rather less fecund in a positive feedback loop: because nothing is growing in these little bands, they cannot retain water well.

This is not all bad. At some point the grass uses its height to seed effectively. The high stalk allows the seed to be carried away on the wind, hopefully taking root somewhere new and fertile and, pointedly, far away from the parent so that it will not compete directly. All of this also creates competitive space for alien species that are good at the hard drier soil between clumps. This will create a new and different diversity provided there is a lot of water.

There isn’t a lot of water. The path maintenance prevents the wetlands from overflowing into the park.

And so then they cut the grass. Now there are patches of short grass all over the park. This short grass needs lots of water but the soil is no longer suited to holding a lot of water — grass gone to seed needs constant external influx of water because it doesn’t bind the soil the same way that asexual grass does. Oh crap! So this truncated sexual grass dies. Now you have a fucking desert in the making. Worse, there’s not really a way to nurse it back to health because the change in the soil is so dramatic. You need to till the whole thing under and add water or rip it up and re-sod with manufactured asexual happy cooperative grass.

Or let the swamp in. The swamp knows all this stuff and knows how to maintain it. Skunks are cuddly!

–BMurray