Threats to biodiversity when controlling wildfires

I am just returning from what used to be called The Sunburnt Continent, but is now more likely referred to as The Burning Continent — Australia. The latter epithet comes from the high propensity for producing wildfires — those that consume the surrounding natural environment rather than being restricted solely to human constructions (e.g. building fires). *

When I used to live there (a couple of decades ago), as a scientist I studied the effects of wildfires on the native plants, and especially on the effects of attempts to control or prevent those wildfires. Given the recent concern about wildfires in wine-making regions, especially in France (eg. Vintners despair after French wildfire ravaged grapevines) and the western USA (Wildfires have ravaged Napa Valley: will California’s wine industry survive?), I thought that it might be worthwhile to present a perspective from outside the wine industry. The issue of fire management is far more complex than simply protecting the vineyards and wineries.

Let’s start with where on Earth wildfires are most prevalent. These are locations with what are called Mediterranean Climates. These climates are ones with hot dry summers and cool wet winters. Given that description, it is not surprising that fires occur quite frequently during the hotter and drier months of the year.

This climate type is located in those places shown in the following map, although you will find that fires are also prevalent along the south-eastern coast of Australia (which is where I used to study them). You will note that this climate type covers a lot of the world’s wine-making regions, because grapevines grow very well in Mediterranean Climates.

This immediately creates an obvious management conflict between grape-growing and fires. In this sense, wine-makers need to accept this conflict as a natural part of their agricultural environment. They don’t have to like it, of course, but they do need to recognize the inevitability of the conflict, given their operating climate.

The reason why this conflict has become more and more concerning is, of course, climate change (Climate change is causing more wildfires and governments are unprepared, says U.N.). The Mediterranean Climate zones are now getting hotter summers and drier winters; and this combination increases the number and severity of the fires. As I have mentioned before (Statistical variance and global warming), climate change is not just about global warming — the warming creates a more variable climate, in this case both hotter and drier. This leads to droughts, of course, as in the western USA news at the moment:

• North Coast sinking back into ‘Extreme Drought’
• West megadrought worsens to driest in at least 1,200 years
• NOAA: California drought continues for 3rd year as ‘driest on record’
• U.S. drought conditions to persist and expand 
  
• Drought in ’21 cost California ag $1.1 billion
  

The National Oceanic and Atmospheric Administration has a map suggesting that the entire western half of the USA has a high probability of the current drought continuing. Drought increases stresses and deaths of forests (Drought year three in California, 2022); and, in addition, this weather change increases the chances of fire occurring and propagating (Likelihood of extreme autumn fire weather has increased 40%). Furthermore, the fire regime (defined below) may be very different to what we have been used to in the past (‘A deranged pyroscape’: how fires across the world have grown weirder), not least because Older wildfire smoke plumes can affect climate.

A Mediterranean Climate creates what we call a Mediterranean-type Ecosystem, or biome. This is a specific combination of plants and animals that live and thrive in that particular climate. Importantly, these plants and animals usually live nowhere else — they have characteristics that allow them to comfortably survive the hot summers, and they do not like it when the  winters get too cold.

The Mediterranean-type vegetation is distinct enough to have been given a set of particular names, such as “garrigue” or “maquis” in the Mediterranean Basin, “chaparral” in California, “fynbos” in South Africa, and “matorral” in Chile. In Australia, the vegetation include heathlands, woodlands and mallee.

The existence of these specific ecosystem names emphasizes the important point that I am going to make in this post. Since these ecosystems are subjected to repeated wildfires naturally, the plants and animals need to have characteristics that allow them easily to survive those fires. Eucalypts (“gum trees”) are the best-known example, which produce epicormic shoots immediately after a fire (see the bottom picture). Originally from Australia, these are now the most widespread trees in Mediterranean Climates, having been actively introduced by people. You will see many of these trees right next to vineyards throughout the world (see the picture above and the second one below).

Far more importantly, though, many of the plant species actually need the fires, in order to complete their life-cycles. That is, heat plays an important role in carrying on their yearly activities. These activities include flowering immediately after a fire (see the bottom picture), releasing seeds only after a fire, and seed germination only after a fire (see the second picture below). (This is a similar idea to marine animals needing to live in seawater, rather than freshwater, and carnivores needing to eat meat, rather than being vegetarians.)

So, many of the plant species are what we call “fire-dependent”. If you remove the fire, or drastically change the fire characteristics, then the plant species will be dramatically affected as a consequence. Indeed, many of them will become locally extinct. This means that there is often a basic conflict between biodiversity conservation (in which the plants must be protected for future generations) and the protection of human life and property (for the current generation).

I have included below a list of my scientific publications on this particular topic — the effects on the plants of changing the fire characteristics. I will not go into detail here (I would lose most of my readers, even though I find all of it fascinating). However, the basic fire characteristics (the “fire regime”) that can change are:

• intensity (how hot the fires get)
• season (when they occur during the year)
• inter-fire interval (the time between consecutive fires).

Natural wildfires tend to be hot, to occur in summer, and to be quite a few years apart. The management issue, then, is simple — any attempt to change even one of these characteristics can have dramatic effects on the abundance of many of the plants.

There seem to be two main human management responses to wildfires. One is to try to prevent them (eg. The Napa County Board of Supervisors has unanimously voted to place a sales tax to fund wildfire prevention projects over the next decade). In general, this has proved to be impractical; and the methods used are not environmentally friendly (Effects of the fire retardant Phos-Chek on vegetation in eastern Australian heathlands).

The second approach is to “fight fire with fire”. That is, we burn the vegetation before the next wildfire comes, and we burn it in a way that remains (more or less) within our control. We call this controlled burning or “prescribed burning”.

This latter management strategy involves monitoring the build-up of burnable fuel in the native vegetation, and then deliberately burning it before a wildfire starts (Wildfire Fuel Mapper helps landowners manage vegetation). The wildfires cannot occur after our burn, because there is insufficient fuel.

Part of the argument for this second approach is that the native peoples of both Australia and the western USA used “controlled fires” to manage their fire-prone landscapes, before the Europeans invaded:

• To manage wildfire, California looks to what tribes have known all along
• California’s wildfire policy totally backfired. native communities know how to fix it
• ‘Fire is medicine’: the tribes burning California forests to save them
• Californians are turning to Indigenous groups and their ‘controlled burns’ to combat the worst wildfire season in history

However, it is very important to recognize that these peoples managed fire for their own cultural purposes, which were not necessarily biodiversity conservation as we know it today (nor were they interested in protection of vineyards). In that sense, being native does not make you “right”, in terms of managing the local environment, it just makes you different to people of European heritage.

Anyway, the main consequence of prescribed burning (other than preventing wildfires) is quite straightforward — it changes the fire intensity from hot (or very hot) to something much less hot, plus it changes the fire season from summer to autumn, plus it drastically shortens the inter-fire interval. That is, prescribed burning involves frequent low-intensity fires in autumn — we change all three of the fire characteristics, simultaneously. My scientific work was all about demonstrating just how much this changes the plant biodiversity, of the east coast of Australia. For many species, the appropriate word is “decimation”.

Needless, to say, management of wildfires is a big issue, especially where agricultural practices are concerned. For example, the affect of smoke on wine is becoming obvious (How do wildfires affect wine? A new study finds out), and this is a big issue for both grapegrowers and winemakers (Grape growers and winemakers try to decide who bears the cost of smoke damage). Research is, of course, being done (When smoke gets in your vines; Australian university finds new strategy to prevent smoke taint in wine grapes).

So, my point in this blog post is that trying to manage fires for one purpose only, usually protection of human property in the broadest sense, has other consequences, unintended though they may be. Fire management is complex. When we are dealing with natural ecosystems (as we are when we talk about biodiversity conservation), management conflicts will inevitably arise. We cannot change the fires without changing the plants, because the wildfires are a natural part of the plants’ environment. Media attention is, not unexpectedly, focused on the loss of property; but there is more to lose than that. We should all care about the bigger picture, as well.

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1. Morrison, D.A., Cary, G.J., Pengelly, S.M., Ross, D.G., Mullins, B.M., Thomas, C.R., and Anderson, T.S. (1995) Effects of fire frequency on plant species composition of sandstone communities in the Sydney region: Inter-fire interval and time-since-fire. Australian Journal of Ecology 20: 239-247.
2. Cary, G.J., and Morrison, D.A. (1995) Effects of fire frequency on plant species composition of sandstone communities in the Sydney region: Combinations of inter-fire intervals. Australian Journal of Ecology 20: 418-426.
3. Morrison, D.A. (1995) Some effects of low-intensity fires on populations of co-occurring small trees in the Sydney region. Proceedings of the Linnean Society of New South Wales 115: 109-119.
4. Morrison, D.A., Buckney, R.T., Bewick, B.J., and Cary, G.J. (1996) Conservation conflicts over burning bush in south-eastern Australia. Biological Conservation 76: 167-175.
5. Torpy, F.R., Morrison, D.A., and Bloomfield, B.J. (1999) The influence of fire frequency on arbuscular mycorrhizal colonization in the shrub Dillwynia retorta (Wendland)Druce (Fabaceae). Mycorrhiza 8: 289-296.
6. Morrison, D.A., and Renwick, J.A. (2000) Effects of variation in fire intensity on co-occurring species of small trees in the Sydney region. Australian Journal of Botany 48: 71-79.
7. Morrison, D.A. (2002) Effects of fire intensity on plant species composition of sandstone communities in the Sydney region. Austral Ecology 27: 433-441.
8. Knox, K.J.E. and Morrison, D.A. (2005) Effects of inter-fire intervals on the reproductive output of resprouters and obligate seeders in the Proteaceae. Austral Ecology 30: 407-413.

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* As Murphy's Law suggests must happen, rather than fires, the Australian east coast has experienced floods this year, with historically high total rainfall (Flood map and rain charts show extent of Queensland and NSW disaster). Mind you, the rescue service in Sydney has said that the damage after the floods can be compared with the violent forest fires in 2019 and 2020.