Wildfires are increasing.
In Australia, Alaska, and California, Portugal, Indonesia, and even the Amazonian rainforest, along with many other countries across the world and states in the US, forest fires are burning more and they’re burning for longer.
Are there any fire-resistant tree species that could help to stop the spread of these deadly blazes?
First, About Forest Fires
Forest fires aren’t always a bad thing. Lightning-ignited fires have always been a part of the life cycles of some forests, clearing up dead undergrowth and making space for new trees.
Some tree species, such as the jack pine, have even evolved to be fire-dependent: their cones only open on exposure to very high temperatures.
Natural fires tended to be self-limiting. They generally occurred during warm and dry times of year, and their burn time and spread were restricted by the availability of fuel. In a healthy forest ecosystem and a balanced climate, that fuel would generally only be old, dead, or dried material.
Why are there so many fires?
Unfortunately though, climate change has meant that fires are now occurring — and raging out of control — far more often than before.
Now often begun by humans, from a still-hot chainsaw put down on dried grass to embers from a barbecue or a cigarette thrown out of a car window, wildfires are destroying habitats and claiming lives like never before.
Some catastrophic fires are even started deliberately by farmers burning land to clear it for agriculture or to generate ash to fertilize the soil.
Conditions in many places around the world have become drier and hotter due to the changing climate. Spring, with its warmer weather, comes earlier. Less rainfall means that trees and soil are drier, and warmer temperatures cause additional evaporation of precious moisture from the forests. Forests become tinder boxes, and a small spark can ignite everything.
Increases in temperature can also lead to increases in the frequency of lightning. In a forest already dried out, where nearly everything has become fuel from lack of rainfall and humidity, an abundance of lightning strikes will be disastrous.
How much is burning?
In 2015, more than 10 million acres burned in the United States. That’s an area equivalent in size to Switzerland or the Netherlands, and historically unprecedented in the US. But if that sounds bad, consider that, in 2020, 46 million acres burned in Australia.
Fires are also being worsened by deforestation. In 2019 and 2020, millions and millions of acres of the Amazon burned, and the fires create a vicious circle as the more trees are lost, the more potential for fire there will be.
What can we do about it? The point of this article is not wildfires specifically, so I won’t go into the social, political, and economic measures that need to be taken.
However, there are some on-the-ground (or in-the-forest) things that can be done to prevent fires and slow their spread, and planting fire-resistant trees is one of them.
Not lighting fires during dry seasons, not unintentionally doing anything that might start a fire during dry seasons, and working to reduce your carbon footprint are also good places to start.
What Kind of Tree Does Not Burn?
I will first just point out that, ultimately, all trees burn. They’re made of wood. That said, there are certain types of tree that are more resistant to fire: trees that take longer to ignite.
It’s these types of tree that you’d want to consider planting on your property as a firebreak. They can stop or slow the spread of wildfires, protecting people, homes, and more sensitive ecosystems.
It’s always vitally important to remember though that just because a tree is fire-retardant or fire-resistant doesn’t automatically mean that you should plant it where you are. You still always have to take into consideration whether it’s a good tree for your climate, soil type, and location.
It’s also critical to bear in mind not all fire-resistant species of trees will be native to your environment. Planting a patch (called a stand, officially) of non-native trees as a firebreak or for any reason might cause other problems.
It’s always best to plant those trees which have evolved to live in your area and which harmonize with the local ecosystem.
And in fact, native trees generally tend to be more resistant to fire. For example, after calamitous wildfires in Portugal, where the imported eucalyptus trees blazed like torches, native oak and chestnut remained.
If in doubt, consult your local agriculture or forestry department, qualified arborist, or tree conservation charity for advice.
What Trees are Resistant to Fire?
With the above in mind, you may wonder exactly which trees are fire resistant. The lists are long, but I’ll start with perhaps the most important: the Mediterranean cypress.
After a devastating fire in Spain in 2012, the Moya brothers — one a botanist, the other an environmental engineer — were amazed to discover that a stand of Mediterranean cyprus trees on their land had almost all survived the blaze which claimed 50,000 acres of forest.
The Mediterranean cypress is not fireproof, but it may be as close as a tree can get. Researchers have found in a lab that the Mediterranean cypress can withstand fire conditions for up to seven times as long as other trees before it ignites.
This is largely due to the tree’s thick, scale-like leaves. They retain water extremely well and keep the Mediterranean cypress moist when other plants and trees would have already dried out. Their fallen leaves retain water too, forming a closely-packed carpet on the floor of the forest, a bit like a sponge.
The Mediterranean cypress’s success at resisting fire may also be due to the structure of the crown of the particular variety being studied. Cupressus sempervirens var. horizontalis have a sparser canopy than that of other trees, even than other types of Mediterranean cypress, and dead leaves and branches tend to fall to the ground rather than remaining in the treetop.
Beyond the Mediterranean cypress’s extraordinary ability to withstand fire, there are other trees that burn less readily. In general, they’re trees with a high moisture content and those that can retain water longer than others.
Opinions vary. While most varieties of oak are generally considered fire resistant (more on that below), lists of fire-resistant trees can differ significantly in their contents even within the same overall region. I’ve seen two lists for California, both written by professionals, which contain different trees.
However, even in that case, the discrepancies could be down to the fact that California is a big place. As mentioned above, just because a tree is fire resistant doesn’t mean that you should plant it in your particular area.
If you live in an area at risk of wildfires — and sadly more and more places are now — I would strongly advise you to seek advice from your local arborist, fire department, or forestry agency. The information given here is no substitute for the guidance of professionals who truly know trees, fire, and the relationship between the two.
In Australia, fire-resistant trees include:
- Salt River gum (Eucalyptus sargentii)
- Lilly Pilly (Syzygium smithii or Acmena smithii)
- Silver Banksia (Banksia marginata)
- Coastal Wattle (Acacia cyclops)
- Swamp Sheoak (Casuarina obesa)
In California, trees planted to resist forest fires might include:
- Coast live oak (Quercus agrifolia)
- Blue oak (Quercus douglasii)
- Vine maple (Acer circinatum)
- Desert-willow (Chilopsis linearis)
- Western redbud (Cercis occidentalis)
- Pacific wax myrtle (Myrica californica)
- Fruit trees in general are often thought to be fire-resistant, and orchards are sometimes used by firefighting crews as natural firebreaks.
- Golden rain tree (Koelreuteria paniculata)
- Gingko (Gingko biloba)
- Various species of ash (Fraxinus spp.)
And elsewhere (and in Australia and California too):
There are a lot of lists stating a lot of different trees as fire resistant, but not all of the information is substantiated. It might be right, but it might not be.
Of the more or less verified information that I, as someone who’s neither an arborist nor a firefighter, can find, here is a selection of the main candidates.
Please note that none of these trees is fireproof. As I said above, all trees burn. These are just some of the trees that foresters and fire service professionals recommend as being safer and more resistant to fire.
- Oak, as already mentioned and as I’ll discuss further in a minute (Quercus spp.)
- Mulberry, specifically White mulberry (Morus alba)
- Chestnut (Castanea spp.)
- Olive (Olea spp.)
- Elderberry (Sambucus spp.)
- Chinese pistache (Pistacia chinensis)
- Carob (Ceratonia siliqua)
- Citrus, including lemon and orange (Citrus spp.)
- Loquat (Eriobotrya japonica)
- Macadamia (Macadamia integrifolia)
- Sycamore (Plantanus spp.)
- Walnut (Juglans spp.)
- Poplar (Populus spp.)
- Big leaf maple (Acer macrophyllum)
- Alder (Alnus spp.)
- Beech (Fagus sylvatica)
- Strawberry tree (Arbutus unedo)
- Bay Laurel (Laurus nobilis)
- Magnolia, although possibly not all varieties (Magnolia spp.)
- Fruit trees in general — apple, pear, stone fruit, etc. — as mentioned above
What do these trees have in common?
What you’ll notice about the majority of the fire-resistant trees listed here is that they’re mostly deciduous (i.e., not coniferous). Deciduous trees tend to have more fleshy and watery leaves that retain moisture well.
Fire-resistant trees may also have thick bark that provides insulation to the trunk against heat and fire. They also tend not to have branches low to the ground.
On the contrary, trees that burn well may have loose, fibrous bark. They’re often very resinous trees — in terms of both their leaves and their bark — with a high volatile oil content. Their foliage is dry and prone to drying out, and they may retain dead leaves and small branches rather than dropping them to the ground.
Many types of pine tree, most cypresses (the Mediterranean cypress is a notable exception), and many trees in the eucalypt family are all extremely dangerous in fire zones.
Are Oak Trees Fire Resistant?
Fire resistant, yes. Fireproof, no. Oak trees (Quercus spp.) always come top of lists of fire-resistant trees, and the cork oak (Quercus suber) is one of the species of oak most able to resist wildfires. The thick cork bark protects the tree from catching fire, and it also protects the tree’s cambium from damage.
The cambium is the cell layer of trees, underneath the bark and the phloem, from which new wood grows and from where new buds originate. The protection that cork bark offers to the cambium of cork oak trees means that they are often able to regrow after fires.
The problem with cork trees though is that, after the cork is harvested, the tree’s fire resistance is thought to diminish until the bark regrows. As that can take years, there must be a balance between cork oak planted for cork and those planted for fire safety.
In general, oak trees, and more specifically whatever variety of oak tree is native to your area, might be a good choice for fire-resistant planting. However, as with any tree choice for fire safety, it’s best to seek the advice of a qualified professional first.
If You Live in a Fire Zone
No tree will offer complete protection against fire, but with sensitive and considered planting, you can create a landscape that is more resistant to wildfires.
By working in conjunction with professionals in your area, you can plant trees that create a natural firebreak and give you the best chance of stopping a fire’s progress.
Planting fire-resistant trees is as important as not planting trees that have a propensity to burn, and careful research may be required to find the most fire-safe and most native trees for your area.
Wherever You Live
The increasing threat and reality of forest fires mean that we must all take responsibility for the ecological impact we have on the planet.
By working to reduce climate change and prevent further climatic shifts, everyone, whether you live in an environment prone to fire or not, can help to minimize the devastating effects of forest fires.