I didn’t intend to write this blog. I started to write another post on patch mosaic burning. But I got stumped by a simple question. I realized that the blog I intended to write would founder if everyone answered that question differently. So this week’s blog contains a quiz, a poll, to see how everybody interprets my puzzling question.
We all know the phrase ‘patch mosaic burning promotes diversity’. It’s a simple phrase but it leaves a lot unsaid. The comparison is hidden. If patch mosaic burning promotes diversity, then it must create more diversity than some other kind of fire regime.
My puzzling question is – what comparison do you have in mind when you say ‘patch mosaic burning promotes diversity’? What is it that you compare patch mosaic burning against?
I’ve never heard the question asked before. So I created a quiz to allow everyone to express their view in a simple and anonymous way. I’d love it if you joined in and voted.
My patch burn mosaic scenario
Picture a large, flat, uniform landscape covered with native vegetation. The climate, soils and vegetation are everywhere the same. Unfortunately the entire region gets cleared, leaving just four, isolated remnants. The vegetation in each remnant is intact and diverse, with few exotic species. All four remnants are identical except for one thing. Each has a different fire history.
- Remnant 1 was completely burnt recently. It now contains very young vegetation.
- Remnant 2 was completely burnt long, long ago and hasn’t been burnt since. It now contains very old vegetation.
- Remnant 3 was completely burnt a moderate time ago. It contains vegetation of ‘intermediate’ age.
- Remnant 4 is different. By freakish coincidence, the fires that burnt remnants 1, 2 and 3 also burnt part of remnant 4. One third of remnant 4 was burnt recently, one third was burnt long ago, and one third was burnt a moderate time ago.
Remnant 4 contains a patch burn mosaic, and Remnants 1, 2 and 3 contain no mosaics.
A group of ecologists surveyed all four remnants and calculated the species diversity of each remnant. (Species diversity describes the number and abundance of species across each entire remnant). Some remnants had greater species diversity than others. This difference was attributed to the different fire histories.
Patch burning is better than … what?
Back to the question that triggered this blog…
If you wanted to check whether patch mosaic burning did indeed ‘promote diversity’ at the remnant scale, which remnants would you compare?
Obviously, you’d compare the diversity of Remnant 4 – the remnant with the patch burn mosaic – against the diversity of some or all of the other remnants. The question is, which ones? The animation below describes your options. (The animation loops continually. You can make it start again by refreshing your web page).
To check whether patch mosaic burning does promote diversity, I would compare the diversity of Remnant 4 (the remnant with the patch burn mosaic) against the diversity of:
If you find the comparison perplexing, don’t worry, you’re not alone. This isn’t a trick question but it is surprisingly hard to answer. If you want to, please write a comment below to describe your thoughts.
Is this the right question to ask?
If you do write a comment, please don’t jump in to claim, ‘Ian, this is beside the point. The important question is … something completely different.’
A number of people said this when I asked my colleagues the question. But each person thought a different issue was important, like: ‘We really need to know about the socio-economic resilience of the region’ or ‘The key question is whether patch burning saves more lives and property’ or ‘You should be asking which fire regime conserves the species we really care about, the endangered species’.
These are all important topics. But they don’t answer the simple question about mosaic burning and remnant diversity. (To be honest I think some people asked other questions to avoid thinking hard about the first question). Importantly, to answer some of the other questions, we still need to ask ‘which remnants would you compare against the mosaic?’
You can stop now if you wish. The quiz above contains the main question I’d love you to answer. However I thought some readers might think about mosaic burning in a different way. So I made a second quiz with a different mosaic. Feel free to answer this quiz instead of the first one if you prefer. Better still, try both.
Imagine four remnants that are exactly the same, with the same fire history. Then one hot summer:
- Remnant 1 gets completely burnt at high intensity
- Remnant 2 is completely unburnt
- Remnant 3 is completely burnt at low intensity, and
- Remnant 4 is burnt in a patch mosaic. One-third burns at high intensity, one-third at low intensity and one-third is unburnt.
You want to check whether patch mosaic burning promoted diversity at the remnant scale. The question is – which remnant or remnants do you compare remnant 4 against? The options are as follows:
Please vote and leave a comment below. The poll will be open for one week only. I’ll discuss the questions and comments in the next blog. The more votes the better, so please discuss the question with your friends and colleagues, and encourage them to vote too.
To simplify the questions, I included just four remnants, each with a different fire history. If this was a robust experiment, many replicate remnants would be sampled. For example, a study might contain 40 remnants, with 10 burnt long ago, 10 burnt recently, and so on. Replication aside, the logic of the quiz would be the same.
Many thanks to this week’s fact checkers, Tim Barlow, Dr Gillian Earl, Dr Dale Nimmo and Dr Simon Watson, who greatly improved my descriptions of the scenarios and quiz options. The original version of the top photo is from the ABC.
- Burning (for) biodiversity: what is a patch burn mosaic?
- Ageing the mallee: a history in burnt trees