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?
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).
Have you worked out an answer? If so, please vote in the poll below.
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?’
Prefer a different 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:
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:
Polling closes
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.
Footnote
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.
Acknowledgements
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.
Ian Lunt Ecology 
Great questions Ian.
Precise timing is not something I’ve previously given much thought to, having simply accepted the general consensus of ‘mosaic burning creates more diversity’.
I suppose it depends mostly on habitat type and also what species you may specifically be studying. Some plants regenerate quickly after fire, some might take longer. Some animals need mature plants rather than new shoots to attract them to an area, or to provide shelter from predation.
As for choosing which option to compare the mosaic burnt area against – if there’s an option to increase our understanding of the effect of fire on species diversity over time by studying a number of comparable areas, then we should definitely do so – providing time and resources permit – which is why I chose ‘each of the other remnants’ for both of my answers.
Hi Dayna, thanks for writing in. The answer to the question ‘does mosaic burning promote diversity’ might perhaps differ between ecosystems. But I’m still curious – should the way we ask the question differ between ecosystems (ie should we compare mosaics against different things in different ecosystems), or logically should we have the same approach across all ecosystems (although not all options will necessarily be relevant or available in all ecosystems)? Lots to think about! Best wishes Ian
Hi Ian,
Can you give me a couple of examples of the ‘different things’ in an ecosystem that we might be comparing mosaics to?
I think you’re referring to factors influencing species diversity, but if you’re comparing areas then ideally you’d want them to be as similar as possible except for the variable(s) that you’re studying, right? So then it depends entirely on your chosen environment. (Doesn’t it?)
Also, to answer your first question “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?” (which was not what the polls asked) I have always imaged it to be a completely burnt area. Eucalypt forest of blacked tree trunks, next to no ground cover, that greens quickly but takes a very long time to recover and lose that look of having been burnt. I only have that imagine because that’s what I’ve seen. I don’t have personal experience of other burnt habitat types.
Hi Dayna, sorry I phrased that poorly in my reply above. I meant to refer to the remnants in the poll question when I said ‘different things’. The scenarios above assume that everything is exactly the same in all four remnants, other than fire history. I didn’t mean to introduce any other variables. What I should have said was… do you think the answer to the poll questions above (ie which remnants would you compare mosaic burning against?) would differ between different ecosystems, or would we logically answer the quiz the same way for all ecosystems? I hope this makes more sense! Best wishes Ian
Hi Ian, Thanks for clarifying 🙂 My answer would not differ between ecosystems. But I look forward to reading more comments from your other followers to see what they think. Regards, Dayna
I chose “none of the above” for each answer – because this appears to be the kind of question that needs an independant vegetation condition benchmark, such as Biometric in NSW, Tasveg in Tasmania and presumably similar systems elsewhere. I understood Tasveg to establish assumed benchmarks for pre-European altered native vegetation condition for a range of vegetation communities, to stand as widely accepted standards over time. Otherwise how can you standardise diversity measurements if you keep changing the goalposts? These benchmark methods have their critics and drawbacks but are continually being refined and improved. They provide a useful and thought-provoking template for research and monitoring patch vegetation over time, rather than re-inventing the wheel.
Hello Gwen, thanks for a great comment, it’s made me think about the question in a different way too. On one hand, I think benchmark schemes and diversity measures do compare very different things. Benchmark schemes compare the condition of a patch against an historical benchmark. These schemes usually include many structural features, such as the abundance of old-growth trees, shrubs, the presence of young regeneration, as well as some estimate of diversity, such as the number of native plant species in the plot.
Comparisons of diversity don’t assess structural features, and simply compare the number and abundance of species between different areas. For example, a study may compare the diversity of native birds between areas with mosaic burning and unburnt areas (or against any of the other comparisons shown above). These comparisons usually also don’t have any historical connotations, they just compare two or more different things at the time of the survey. They just ask, which fire regime promotes the most diversity, patch burning or something else?
I think both approaches are very valuable as they assess different things. What’s interesting though is that some people may include a historical reference point in their mind when they they about mosaic burning, whereas others don’t. If that’s the case then it highlights another reason why conversations about the topic can go round in circles because different people are comparing different things – which is the one of the goals of these blog posts, to try to explore how people think about the topic.
I hope I haven’t misinterpreted your points at all. If so, please correct me. Best wishes Ian
Another great post, thanks Ian! You’ve got me thinking on a Sunday morning, and that’s not an easy thing to do…
I had to go with comparing each of the remnants with remnant 4, simply because species respond differently to changes in veg post fire and comparing the mosaic to only one (surely) would lead to a false answer. If we wanted to sample species diversity and compare it to see where it is highest, wouldn’t we need to account for the fact that remnant 4 itself represents a sample of all three other remnants and their communities? Quokka, for example, prefer thickets and dense undergrowth as their habitat, so they tend to be found in areas that haven’t been burnt for a long time, while a lot of other small mammals (particularly rodents) move into burnt patches v soon post-fire to take advantage of newly exposed resources or new growth. I would assume that the same sort of patterns hold true for vegetation as they do for fauna? Surely if both of these groups made up the hypothetical communities in, say remnant 2 (long time since burn) and remnant 1 (recent burn), they could BOTH be present in remnant 4?
Hi Carly, thanks for another great comment. You highlight how important the issue of scale is when we answer the question. At one extreme, we could argue that at the regional scale (ie the bigger scale that includes all four remnants and the surrounding cleared area) all of the four remnants contribute to a mosaic – as each contains a different vegetation structure due to the different fires. However, if we look at the question at the scale of the individual remnants (which is the way I wanted to phrase the quiz questions) then we need to compare diversity at the remnant scale only.
At the remnant scale, remnant 4 (the mosaic) has a small area that is the same as in Remnant 2, and a small area that is the same as in Remnant 1, and another like Remnant 3, as you point out. The biologists who did the surveys would have added up all of the species in all of these areas to calculate species diversity across the whole of each remnant, so they could work out which remnant supports the most species. I hope this makes sense! Best wishes Ian
I agree with you both Carly and Ian, scale. it’s all about scale
Hi Peter, yes scale is critical in this issue, as it ultimately is in most topics in ecology. One point I’d like to make, more for the benefit of everyone who reads this for the first time, is that while we can examine the question at different scales, the quiz question has a very specific scale. It focuses on diversity at the remnant scale, ie at the scale of each whole remnant, not the broader landscape, or the burnt patches with each remnant. This isn’t necessarily the ‘best’ scale to study (that depends on our aims), but asking the question at one specific scale means that the question is a little more tractable, and more likely to be interpreted the same way by lots of readers. Thanks again for writing in, best wishes Ian
Ian,
I’ve always considered your posed question of “patch burning promotes biodiversity” to mean that it results in or allows a greater level of biodiversity than a complete burn covering the whole landscape.Unfortunately the usual measures of biodiversity conducted by land managers are restricted to vegetation, with minimal, if any, measurement of fauna, fungi. This is assuming that pre and post-burn monitoring actually takes place at all. Maybe your question needs to be reworded to “what sort of burning regime do we impose on a particular landscape in order to, at a minimum, preserve existing biodiversity and, ideally, improve it?” And burning regime can include no burning at all.
Hi Colin, yes, good points. Focusing first on your first point… This is the comparison that the quiz asks, but the quiz extends it a little and asks – do you compare the remnant that was burnt in a mosaic against a remnant that was completely burnt recently (ie against remnant 1 above) or against a remnant that was completely burnt a long time ago (ie against remnant 2 above) or against remnant 3? All of these remnants were completely burnt. Why is one option more appropriate than another?
The question you ask above is a great one, and something we should all aim to achieve. But if we wanted to work out what the best fire regime for promoting diversity was, we still come back to the question – what would we compare a mosaic burn (or any other option) against? The quiz question doesn’t ask, how should we burn or what should our aims be, it just asks a much smaller ‘simpler’ question, if we wanted to see whether mosaic burning promoted burning, what would we compare it against? Thanks again, best wishes Ian
Ian
Just as for patch diversity, we might need a little more diversity of quiz answers…! In each quiz, the option I was looking for was that we should compare the patch-burn mosaic to each of the other remnants individually, that is, in three single comparisons rather than any type of multiple comparison. Then, if the patch-burn mosaic were found to be more diverse that any one of the other remnants, that would suggest patch-burning is the way to go.
While that may be the answer now, adding the element of time changes everything. If the patch-burn remnant is sufficiently large and patchy to allow species to move (as individuals or as propagules) and colonise areas at the preferred stage post-fire for those species, then all species should be able to persist in that remnant indefinitely, through a continuing series of patch burns – an important goal. However, when each single-age remnant ages and is reburnt through a series of fires that each burn the remnant completely, it will become simplified to contain only those species that can persist through the entire fire-cycle at one site, and furthermore only a subset of these species will be apparent to the visitor at any time. It would seem that only the patch-burn approach has the potential of maintaining all species indefinitely in a sufficiently large remnant.
Adding the element of time doesn’t change the proposed answer to your thought-experiment (that we should compare the patch-burn mosaic to each of the other remnants individually), but it does also suggest that there is no independent single-aged vegetation condition benchmark – or rather that the benchmark vegetation condition might best be a landscape of multiple post-fire ages.
Hi Steve, thanks for a great comment. I re-worded the quiz options a few times before I posted them to clarify them as much as I could, however they still seem open to different interpretations. The option ‘I would compare the diversity of Remnant 4 (the remnant with the patch burn mosaic) against the diversity of… each (as opposed to ‘all’) of the other remnants’ was intended to cover your suggestion that “we should compare the patch-burn mosaic to each of the other remnants individually, that is, in three single comparisons rather than any type of multiple comparison’. Apologies for the confusion.
I hope I haven’t misinterpreted your logic, but I think your argument is therefore that – patch burning would promote diversity if the patch-burn mosaic was more diverse than any one of the other remnants, but would not promote diversity if any one of the other remnants had greater diversity than the patch burn remnant. I wonder whether other readers used the same logic as you have when they voted for this option, or whether they used a different argument.
Your point about changes over time is fascinating. It raises a few questions for me. If the key argument for patch burning is to maintain a steady supply of a particular patch type over time, then do we need to worry about the spatial arrangement of the mosaic at any one point in time? Many other arguments about patch burning focus on the importance of the spatial mosaic pattern at one point in time. Is this as relevant if the focus is on changes over time?
Second, your example of changes over time seems relevant to the first quiz above (which compares remnants that differ in the time since they were last burnt). Is it as relevant to the second quiz, in which the remnants differ in the intensity at which they were burnt?
Lastly, your suggestion that a focus on changes over time suggests that ‘the benchmark vegetation condition might best be a landscape of multiple post-fire ages.’ Is this the same as comparing Remnant 4 against all (not each) of the other remnants, in the quiz question above? You’ve suggested lots of great ideas to think about. Thanks once again, and best wishes Ian
Thanks Ian
I suggested that we could conclude that patch burning promotes diversity if the patch-burn mosaic remnant were more diverse than any of the other remnants, but I don’t think the contrary proposition can be stated as easily. So much is dependent on scale – indeed, if any one of the other remnants had greater diversity than the patch-burn remnant, I would first wonder if this wasn’t simply due to the areas of each of the age-classes in the patch-burn remnant being smaller than the areas of the single-age remnants
.
Time adds another layer to the logic, rather than directly replacing considerations about the present. Ecosystems have internal elasticity (over millennia, the area proportion of old-growth forest in a given part of the landscape may have varied between, say, 20% and 80%, due to the stochastic nature of fire), but managing a landscape for species persistence requires us to understand the thresholds beyond which change is not reversible. How much (proportion by area of) recently burnt vegetation can be tolerated without a permanent negative impact on species that require long-unburnt sites? What is the minimum area of recently burnt vegetation that is required for disturbance species to be maintained? And, of course, what is the minimum period required between fires at a site for slowly maturing fire-sensitive species to reproduce and this persist? The mosaic is not just a mosaic of fire-ages across space at the present, it is also a mosaic of fire return intervals over time at each site.
So I don’t see a ‘benchmark vegetation condition’ as being any one static point. That may be more the case in ecosystems where fire (or other disturbance) is naturally very rare, but then those ecosystems are relatively rare across broad sweeps of Australia, and even in those cases excluding fire altogether may eventually have more deleterious effects than allowing occasional fire. Perhaps the next quiz question could ask us readers to articulate our biodiversity goals for managing remnants over time, because without agreed biodiversity goals we cannot agree on the possible fire regimes for any remnant!
Thanks again Steve, there’s even more things to think about. I won’t comment more now, so other readers get to think about the issues, but will try my best to incorporate your ideas when I pull all of the comments together in a later post. Best wishes Ian
Thanks again for your great accessible posts. I love them. In some ways the question you pose today is irrelevant. When dealing with isolated remnants in the landscape, a single fire through an entire remnant can theoretically cause an immediate and permanent extinction within that remnant ( yes I know extinctions by definition are always permanent). This could be a species sensitive to fire or through the destruction of a crucial habitat niche. Perhaps mosaic burning does not so much promote diversity, it immunises against loss of diversity. Therefore the only way to avoid this possibility is to never deliberately burn an entire remnant. The next question to ask then could be, “what is the optimal percentage of a remnant that should be burnt at any one time to best maintain diversity?”
Hello Peter, thanks for writing in. I hope I’m not putting words in your mouth, but I think you are the first person who has suggested that patch mosaic burning might not actually promote diversity? I haven’t picked up this from other comments on this or the last patch burn blog.
As I understand your logic (and again apologies if I’ve misinterpreted you), mosaic burning may lead to more diversity than a complete uniform burn – if burning reduces the abundance of some species, or in the worse case scenario, made some species go extinct. I’m wondering how you envisaged the comparison of the patch burn mosaic against the unburnt remnant. Did you envisage that the mosaic remnant would have higher or lower diversity than the unburnt remnant? And, therefore, which of the quiz options you selected?
Your point about mosaic burning acting as an insurance policy to reduce the chance of a whole remnant burning at once is great. In this case – just to throw yet another question out there, is the most important question “what is the optimal percentage of a remnant that should be burnt at any one time to best maintain diversity?” as you suggest, or would it be, “what is the best configuration of the burnt zone to minimize the chances that the entire remnant gets burnt later on?” Both questions could invoke very different responses perhaps. Thanks again for yet another great comment. Best wishes Ian
I agree the “best configuration” question is also vital. There is some urgency in these questions as whole remnants are currently being burnt by DEPI to help achieve ha targets.
Regarding the unburnt remnant comparison with the mosaic burn, a comparison would be useful but you would expect to find the long unburnt with a reduced diversity. However my understanding is that long unburnt areas can create useful habitat niches that may not occur elsewhere. This whole field of playing god with fire is so complicated.
Hi Ian,
I think it is a great question to think about. I believe that you would need to look at all of the sites equally. There will always be different factors within each that will influence what is there and how it comes back. Mosaics in my opinion are good in one way at least it tends to give refuge for those animals, plants and seeds to survive. The intensities are certainly a large factor as well. Thanks for posing the questions. I too look forward to further posts on the subject.
Terri
Hi Terry, comparing the mosaic against each of the other options is certainly the most popular option so far! Best wishes Ian
I think the answer that is most correct is to compare the patch mosaic remnant to each of the other remnants for both questions. That is to acknowledge that different species and assemblages have different time-since-fire requirements/reactions (and ignores any other distrubances having an impact). Interestingly, biodiversity doesn’t necessarily change post-fire in a uni-directional fashion and so when the actual comparison survey takes place (how long after the fire, time of year etc.) could provide quite different results, but probably only in magnitude.
You compared fire intensity and fire history between patches, but I didn’t notice a mention of fire history within a patch. Assuming equal fire intensity and time since fire, two patches could vary considerably in biodiversity due to the timing and intensity of the second last fire, and the fire before that…and the fire before that etc.
I don’t think that there is a right kind of mosaic burning (I’m talking fire management now, rather than just natural fire) but that for most fire-prone vegetation, small mosaic patch burning is better than broad-scale fire exclusion or broad-scale landscape burning.
Hi Jodie, thanks very much for writing in. I didn’t compare patches with different fire histories, as I wanted to keep the comparisons as simple as possible. But you are right, lots of remnants contain mosaics of patches that have different fire histories. This was discussed a bit in the animation in the last blog on fire mosaics. I thought it would complicate things too much if I added another quiz. Thanks again & best wishes Ian
Maybe three of the sites have diversity associated with time since fire (species lists a, b, c). If the fourth site is to ‘promote / create’ diversity through patch burning (or different times since fire) it should have all the species that are collectively in a, b, and c plus some additional species?
Hi Lisa, thanks for writing in. I think that might be yet another way to approach the issue. The approach suggested by some readers is that mosaic burning would promote diversity if the diversity of site 4 (the mosaic) was greater than the diversity of site 1, and also was greater diversity than the diversity of site 2 and also was greater than the diversity than site 3. If I’ve interpreted you correctly the approach you are suggesting suggests that mosaic burning would promote diversity if the diversity of site 4 (the mosaic) was greater than the diversity of all of the species in sites 1, 2 and 3 when these are pooled together. The quiz has worked really well for showing how many different ways the question could be tackled hasn’t it. Thanks again & best wishes Ian
Hi Ian
Another great post. It highlights the diversity of ways you can think about how mosaics might (or might not) improve diversity. Critically it reiterates the idea that a management target of “creating a mosaic of fire histories” is not a useful goal. Rather, it is important to ask which mosaics will best promote diversity compared to specific other types of mosaics. The types of mosaics that can exist will be defined by combination of available fire histories in the ecosystem, and management interventions (prescription or suppression of fire) through time.
Interestingly, while you present your blog-post in terms of fire, it is equally as relevant to any discussion of landscape heterogeneity. There are even more studies in agro-ecosystems that make proclamations such as “biodiversity will be promoted by increasing habitat heterogeneity at all spatial scales” (check out the otherwise great paper by Benton et al. 2003 TREE(18) for these types of statements). Just like in fire ecology, there is rarely a discussion about what you are comparing the “heterogeneous landscape” to.
Thanks again for the post
Simon
Hi Simon, thanks very much for commenting. Your comment that aiming to create mosaics isn’t a useful management goal echoes one of the key messages from the earlier blog in this series – https://ianluntecology.com/2014/07/06/patch-burn-mosaic-1/ – although in that post the conclusion was reached for a slightly different reason – i.e. because mosaics are so varied that almost any fire pattern can be said to form some sort of mosaic. Thanks for extending the argument to agricultural landscapes, that pushes the argument further than I had dared to do. Best wishes Ian
Hi, Ian, thanks for an interesting quiz! As far as the answers go, I picked what was most popular, ie compare to all the others and see. In the case of the recently/long ago burnt pieces, you also get to compare over time as one other commentator suggested.
One of the complexities implied in mosaic burning is that, if it’s us going out there and deliberately setting fires in some kind of environmental “management” strategy, then we probably shouldn’t be setting our fires in a mosaic based on just random bits of area of a certain size range, nor just on the history (recent and long term) of that bit, or anything – but on a thorough understanding of the biota currently in that patch of bush, and how they respond to fire or its absence. I fear that the “patchwork” implied in this could be patches as small as one or the other side of a small gully, and no more, being burned at one time; very small patches based on microclimate, species present, weather and season, etc. That level of detailed knowledge and understanding of the bush is entirely site-specific and hard to derive from modelling; it’s the kind of knowledge you really have to live there on the land (like indigenous people did) to accumulate. I’m a newbie to academic ecology (just started a BSc) but been around the bush a long time so I hope my feelpinion on this is somewhere in the ballpark!
Hi Ben, thanks very much for a great comment. It’s fantastic to see the breadth of experiences and viewpoints that everyone has brought to the issue. It highlights how many different ways we all view ‘the bush’ and everything that lives in it and happens in it. I’m going to have a tough time bringing all of these ideas together when I try to synthesise the main ideas in a later blog. I know I’ll only be able to scrape the surface. Best wishes with your new degree, I hope you enjoy it and learn lots. Cheers Ian
Many thanks Ian for initiating discussion around the fire ecology topic – a critical issue we need to explore in much greater depth – and apologies for the tardiness of this comment.
My response to the poll question is “None of the above”, because while the listed comparisons will provide useful information to assist an understanding of fire history, none of them can answer the question about whether mosaic burning promotes diversity. This is because an assessment of species diversity across the scenario remnants isn’t going to provide the understanding of the role of fire in ecological diversity that we need. Ecological diversity can be described at the landscape, ecosystem, species and genetic levels. Those levels can be pictured as a pyramid, with the landscape level (smallest diversity) at the apex, progressively widening through the ecosystem and then species levels (increasing diversity) to the genetic base (greatest diversity). Species diversity exists and should be considered across landscapes and ecosystems, and not just within particular ecosystems. If this isn’t done, then we are going to be managing fire to simply promote more species in particular ecosystems, rather than to promote the unique mix of species (and genes) that distinguishes particular ecosystems from others in the landscape.
To be able to manage fire to promote the unique mix of species that distinguishes a particular ecosystem from others in the landscape, we need to try to understand what the ecosystem looked like at the time of European settlement, and what fire regimes were mostly likely to have contributed to the species mix and ecosystem structure that existed at that time. (The time of European settlement is used as the basis for vegetation management legislation and policy in Australia, being the point at which broad scale land clearing commenced, fire regimes that had been in place for a long time began to be dramatically altered, and destructive exotic species began to be introduced). Understanding how fires since European settlement have affected the species mix is very useful to this understanding, but it also requires research, including historical research, into pre-European ecosystems. Anthropologists and archaeologists could assist ecologists with this research.
My own stark realisation about why this ecosystem understanding is critical came in the mid-1990s when I hosted a walk for a group of ecologists from a South African university and the University of Queensland. The walk was through the Dwyer’s Scrub Conservation Park in the southern part of the Lockyer Valley in South-East Queensland, which protects an area of endangered semi-evergreen vine thicket (regional ecosystem 12.9-10.15 http://www.ehp.qld.gov.au/ecosystems/biodiversity/regional-ecosystems/details.php?reid=12.9-10.15). The South African ecologists had been researching these ecosystems in their home country, and as we walked through the scrub they could name almost every genus, both plant and animal, and remarked at how while the species were slightly different, the genera were mostly the same and in the same structure in the communities in both countries. This meant that the vineforest communities in Queensland and South Africa were little changed from when they were the one ancient Gondwanan community, and the last thing we should be doing is carrying out management actions that alter the species mix and structure of such ancient ecosystems.
Moving to such an ecosystem understanding is unfortunately hampered by widespread assumptions in regard to Aboriginal fire regimes. Aboriginal people certainly used frequent planned fires to maintain grassy groundcover in many locations, but as Bill Gammage discusses in The Biggest Estate on Earth: How Aborigines made Australia, they avoided the use of fire to maintain particular ecosystems in other locations (http://www.allenandunwin.com/default.aspx?page=94&book=9781742377483). An ecosystem they would not have deliberately burnt is the above example of the semi-evergreen vine thicket in Dwyer’s Scrub Conservation Park, which is highly fire sensitive.
An ecosystem Aboriginal people are unlikely to have deliberately burnt is found directly adjacent to the semi-evergreen vine thicket in Dwyer’s Scrub Conservation Park, being regional ecosystem 12.9-10.19, a shrubby / grassy open forest to woodland (http://www.ehp.qld.gov.au/ecosystems/biodiversity/regional-ecosystems/details.php?reid=12.9-10.19). I discuss this example ecosystem in a conference paper I delivered in 1998, using the case study of a nearby property I had managed for a few years (http://bruceboyes.info/wp-content/uploads/2014/08/A_Fire_at_Treetops_Fire_Management_and_Nature_Conservation.pdf) (the discussion in the paper refers to an 1886 survey map which I have attached to the paper, and the location of the case study property is -27.759051,152.119432). River flows work I have been involved in since confirms the view I express in the paper that the pre-European fire regime in this ecosystem is more likely to be the result of climatic conditions than deliberate burning. The fire frequency appeared to be a cycle of intense fire every few decades, and this aligns with the flood and drought dominated regime cycles evident in river flows in eastern Australia (Figure 3 in http://bruceboyes.info/wp-content/uploads/2010/01/Shoalhaven_Environmental_Flows_Investigations.pdf). Influencing this regime cycle are the El Niño Southern Oscillation and longer decadal oscillations such as the Pacific Decadal Oscillation (http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_cs.htm), and both are evident in the annual flows graph that is Figure 1 of the same report. It would be interesting to overlay these graphs with a fire history graph for the same catchment. (Note to self: further historical research into the historical evidence for the fire regimes in such ecosystems and/or research on the climate cycle links of the pre-European fire regimes in such ecosystems could be good PhD topics).
The ecosystem-based approach can also be applied to other management issues, as I have done in the Biodiversity Recovery Plan for Gatton and Laidley Shires (http://bruceboyes.info/2004/03/biodiversity-recovery-plan-for-gatton-and-laidley-shires-south-east-queensland-2003-2008/).
Hello Bruce, Thanks for making such a detailed comment. I think you’ve interpreted the question at a different scale than was presented in the poll. The poll question asks “If you wanted to check whether patch mosaic burning did indeed ‘promote diversity’ at the remnant scale, which remnants would you compare?” Thus, the scale that is being compared is explicitly the scale of the remnant, not the broader landscape. Lots of issues come into play when we look at diversity at broader scales. Thanks for providing the links to extra documents too, I’m sure many readers will find them very useful. Best wishes Ian
One issue is the size of the remnant. I volunteer at a 1.6 hectare patch of Themeda grassland in western Victoria, with over 150 native vascular species. It gets burnt once every 3 to 5 years, but the authorities have a strong reluctance to burn anything less than the whole site.
Another issue is that remnants often are not uniform. Most of “my” remnant has the same slope/sun exposure/etc, but about 1/4 of the site contains all the Diuris plants, a 10m x 10m patch contains all the Prasophyllum plants, most Cymbonotus priessianus are in a different 20m x 10m patch, the Stackhousia subterranea move around, … i.e. The plants themselves are patchy!
Hi Mike, thanks for writing in. I deliberately didn’t specify a particular size for the remnant, or what kind of vegetation it contained, as I wanted readers to picture their own favorite ecosystem while they thought about the comparison. The points you raise are very relevant to the practicalities of managing fire regimes in small remnants, but I’m not sure that remnant size influences how we would answer the poll question. Would we answer the question differently if we were managing small remnants versus big remnants? Thanks again, and best wishes, Ian
Hi Ian, I think Mike Wicks comments really highlight the problem. The more we know about plant and animal responses to fire, the more we are obliged to manage them according to our new knowledge. This makes for a very complicated and costly burn prescription. The earlier management objectives of patchy mosaics were based on a simple idea that there would be a higher probability of getting the burn right for more species if different fire frequencies and fire intensities were used, but there is also the risk that what you choose to do in one patch could still be detrimental to the fire sensitive species in that patch. So do we need to understand the fire responses of all the fire sensitive flora, fauna, fungi and invertebrates species within each patch before we get it right, regardless of scale or ecosystem we are managing? Will we ever have enough information about all their fire responses to manage fire to avoid local species extinction either from too much or too little fire? Probably not, but we should be putting much more effort into monitoring the impacts and outcomes of different fire regimes at all scales. The two options to compare patchy mosaic burns against all other fire types (frequency and intensity) is the best possible way of improving our understanding of these important disturbance events.
Hi Ian,
I havent had time to digest all the great responses above but I am often frustrated with some of the conventional thinking around so called “environmental burns”. For a number of years now I have been privately researching invertebrates in box-ironbark forest. Principally elucidating their phenologies. I’ll make the following points from the top of the head:
– Firstly our landscapes are no where near the same as prior to european settlement so fire regimes that influenced them probably need to be questioned ie will they produce the same results?
– Secondly i feel we tend to be veg centric in our approach to these questions. Plants dont move and many other things do and are problematic to assess. We shouldnt assume that just because the veg has re-established that there hasnt been an impact and I think others above make this point also.
– Thirdly different landscapes, different ecosystems possibly different questions and approaches.
– The nature of the fire is and issue. in particular its timing and seasonal settings has I believe a huge influence. In victoria with controlled burns applied in spring and autumn this is potentially a major difference to “natural summer fire occurence”. Spring fires generally prevent understory plants from seeding and if these are preceeded or followed by dry conditions can produce significant failure or lag in re-establishment. Large numbers of invertebrate species appear adapted to summer fires and pupate buried in the soil and litter etc over summer. In old growth settings the condition of both (soil and litter) potentially mitigate fire impacts. In regrowth forests there is more vulnerability. Spring and autumn fires potentially effect invertebrates by either killing larval forms, removing host availability for the next generation or do both.
– In summary I think direct comparisons between different patches is of limited value unless the underlying processes, patch history (and associated environment) and basic biology of the systems is understood. i am distressed that general and supposedly authoritative conclusions are made without understanding this context and its my personal belief that these are often flawed.
– It is not implausible that current thinking around enironmental burning will be seen in a poor light in the future.
Regards Steve
Hello Steve, thanks for writing in. I think you banged the nail on the head with your comment that “In summary I think direct comparisons between different patches is of limited value unless the underlying processes, patch history (and associated environment) and basic biology of the systems is understood”. There are heaps of things we know every little about. The challenge we face is – there are so many things we still need to understand, what approaches can we use in the interim? We will always have to use relatively simple approaches to manage ecosystems compared to the huge array of unknowns that exist unfortunately. Bridging this gap is the biggest challenge for conservation biology I suspect. Best wishes Ian
Hi Ian,
Wow very interesting blog. The effect will also vary according the size of the burn patches, and at what time of year or under what climatic conditions the burn occurs, eg time since how much rain, time from burn until how much rain, temperatures … will all greatly effect how different plants and in turn animals respond to the burn. In my experience as a landholder, ‘mosaics’ that are too small in size or not even/consistent enough within the prescribe burn area are very deleterious as they do not provide adequate protection from bushfire conditions and can result in the entire area suffering a large burn at one time. Also dribbley low-intensity ‘mosaic’ burns tend to repeatedly burn the same areas – usually the hollows where the most fuel load grows – resulting in repeated over-grazing and weeds in these areas. I think that burn SIZE should be designed to control most of the spot-fire risk from a bushfire in a particular plant community – in our area I feel about 6 km. Burn TIMING should aim to imitate what is natural for the area – in our area early summer heat/lightening storms are common natural ignition sources. (I have seen clear evidence of human-lit wet season fires having devastating effects on the natural pastures) And burn FREQUENCY and INTENSITY should be varied. Thank you for questing the blind-flowing and miss-interpretation of ‘mosaic burning’ as I have seen a lot of damage from miss-application of this concept. Regards, Michelle.