Extending the concept of 'old-growth' to microbial communities and systems
The story behind the paper
Some papers have an unlikely story. This is one of the them. One morning, it was on November 25, 2023, I went into the shower, somehow thinking about old-growth grasslands (including the ones I had seen during a trip to China in October that year), and I came out with the idea of applying this concept to microbial systems. I posted the idea on X/ Twitter right afterwards, the very same morning, and it was met with a very enthusiastic response. The post had over 24K views and elicited a lot of feedback in terms of very good comments. When I posted the message (with the rather pretty AI image you see above), I wasn’t so sure if this was an idea worth pursuing. But encouraged by that initial response, I thought a bit more about this, did some background reading, and wrote a short manuscript, the first draft of which was ready in a few days; and this paper was accepted in early January 2024. The original X post is in the acknowledgements.
So what’s this all about?
‘Old growth’ is a term that is usually applied to forests. More recently, this term has also been applied to grasslands as well. I think everybody has an intuitive understanding of what this means, and images of old, gnarly, mystical forests covered in moss and lichens come up. Such systems are precious and need to be protected. That’s the actual power of that term — it is quite evocative.
When I started reading about the terminology, it turns out, as is so often the case in ecology and the environmental sciences, that a clear definition is hard to come by; in fact, there are very many different definitions. But there are some elements with which one can work: they are ancient, structurally complex, generally have high biodiversity, and dead biomass has accumulated.
How could this concept be applied to microbial systems? This at first seems quite counterintuitive, since microbes are considered to be fast-lived, fast-growing, and ubiquitous. So how could they possible be ‘old-growth’?
As it turns out, not all microbes live in circumstances where they can grow fast, since they have to contend with adverse environmental conditions (lack of moisture, lack of nutrients, low temperatures) that make this impossible. Thus, clearly there are are several situations in which microbes will be growing very slowly, and can produce structures that are old. In mention quite a few examples in the paper, including fairy rings formed by fungi, stromatolites or biological soil crusts.
Ok, so far so good. But what is the advantage of applying ‘old-growth’ to microbes?
The term ‘old-growth’ is a metaphor that evokes inherent value: this is something precious that should be protected, because it is valuable, and that should be studied in its own right. If we could convince people that there are old-growth microbial systems, then this kind of value and interest could be extended to these systems as well, perhaps making it easier to protect them and providing renewed impetus for studying them. And I believe this would be a clear benefit to microbial ecology, and in the end, the planet.
What do you think about this concept or the paper? Let me know in the comments, I’d love to hear from you!
Interesting idea. I tend to think of the concept of 'old growth' with a component of a successional endpoint / "climax community". It is less clear to me that slow- to VERY slow-growing microbial habitats fit that paradigm. Old growth forests still exhibit reasonable levels of gross (if not net) primary production (that is, biological activity) whereas several of the examples you cite are beyond 'nutrient-limited' to nutrient impoverished. Are these systems characterized by the capacity of organisms to enter dormant states that minimize maintenance energy costs?
I can't fathom what the physiological state of cells growing with an (apparent) doubling time of many years -- easier for me to think of these as 'average' doubling times -- with >99% cells in a quiescent state and an occasional cell encountering a 'patch' of nutrient resource that allows it to grow.
Best regards,
Allan Konopka
Hi Matthias,
Your illustration is fantastic! I totally agree that old-growth grasslands are as rich and precious as old-growth forests. Sadly, they are underappreciated. In North America, less than 0.1% of the original tall-grass prairie remains, and few realize what has been lost under today's bread-basket.