Month: March 2025

There are many popular songs about fire. Those of you who are fans of Bruce Springsteen will recognize these lyrics from “Dancing in the Dark”. They popped into my head when I was driving home from Asheville NC to Athens GA this past weekend and noticed plumes of wildfires punctuating the air along the highway. That inspired me to write this post on wildfires, which are affecting the Southeast this spring but also affects many areas of the United States and the world too, especially when those areas are in drought. In this post I will discuss how wildfires start, how the local environment may help them spread, and what you can do to protect your properties and gardens from the impacts of wildfires in your communities.

Wildfires versus prescribed burns

Fires in the environment can be caused by natural events like lightning or can be sparked by human sources. Some fires are set on purpose to clear land and reduce fuel loads so wildfires are less likely to occur and some are caused by ignition sources like sparks from dragging chains, a carelessly tossed cigarette butt, or an untended campfire. Some are set deliberately to cause damage and chaos by arsonists or are the result of careless children or adults. According to Earth.org, “40% of wildfires that affect British Columbia in an average year are human-induced. In the US, the amount is more than double, with nearly 85% of the nearly 100,000 wildland fires that affect North America every year caused by human activities, according to data from the National Park Service.”

The fires that are set to reduce fuel loads and remove overgrowth from land are called “prescribed fires” and they are regulated by most states. Farmers sometimes use controlled burns to remove cover crops and prepare for spring planting. Those who want to set a prescribed fire usually have to file a form or follow a procedure to indicate what they are going to burn and when and what the weather was at the time of the burn. They are also expected to file all the necessary permits and notices for smoke and fire hazards. In some states you must be certified to conduct a controlled burn. If the weather is too windy or the humidity too low, they are generally not allowed because the chance of a fire getting out of control is high in those atmospheric conditions. There have been instances of prescribed fires escaping their planned burn areas or causing significant hazards, including a number of deadly multi-car accidents when the aerosols from the fire attracted enough water vapor to form a “superfog” that moved across a busy highway and caused visibility to fall to near-zero feet which blinded drivers speeding down the roads. “Superfog” is especially dangerous if it occurs overnight when the humidity is the highest which causes it to be more dense.

What are the causes of wildfires and how do they spread?

The number one cause of wildfires from natural causes is lightning strikes, especially in areas of drought when the vegetation is very dry and moisture is scarce. Volcanoes can sometimes cause fires by dropping hot embers onto flammable land cover and buildings. Strong winds can quickly spread the fires to new areas downwind and provide a source of oxygen that helps them continue to burn. In areas with a lot of fuel like drought-stricken national forests or open grasslands the fires can rage out of control and cover large areas in short amounts of time.

How to know when you are threatened by wildfire

When conditions are ripe for wildfires, government agencies such as the National Weather Service and state forestry departments will often put out watches and warnings to notify people in areas that are vulnerable to wildfires to be aware of threatening conditions and prepare to evacuate if necessary. If you live in an area that is prone to wildfires, you should make a plan for how to get out quickly and safely and share it with your family and colleagues. If an evacuation order is sent out you should be prepared to move quickly to safety carrying necessary documents, medicines, and valuable property with you in a “go bag” which is assembled ahead of time.

What you can do to your gardens and properties to minimize damage from wildfires

The best way to minimize damage from wildfires is to design your homes with fire-proof or at least fire-resistant materials. In the landscape around your home, plant appropriate plants and keep combustible material at least 30 feet from your home. Create horizontal and vertical breaks in the landscape to slow the spread of flames. Make sure that you have removed low-hanging dead branches and removed any dry shrubs, pine needles, dead grass, and vegetation. You can find additional information on creating fire-safe landscaping here and here. If you live in a fire-prone area you should also be prepared to stay and defend your home if it is too late to evacuate, but this should only be done if you have no other options. If you are able, evacuation is always the best option.

After the fire – other hazards

Hazards caused by fires continue even after the flames are out. Burned-out trees have lower strength and may be prone to dropping limbs or even falling over, creating hazards to anyone or anything beneath them. Ashes may have toxic components that can be carried long distances by the wind or by vehicle tires. In one of my favorite books, The Control of Nature, author John McPhee discusses the debris flows that can occur out west when heavy rain falls on recent fire scars, leading to the destruction of buildings and blockage or destruction of streets and other infrastructure by mud and boulders.

Wildfires are a hazard which can affect any place that has flammable vegetation. Take the time to understand what your risk from wildfire is, plan your landscaping accordingly and you will be better protected from this dangerous natural (and sometimes human-made) disaster!

“Put rocks in the bottom of pots for drainage” is one of the most pervasive gardening myths, because it makes intuitive sense (as discussed in this earlier post). Understanding the science behind capillary barriers (what gardeners call perched water tables) is not only more mentally satisfying than the faulty belief but it can help you avoid other gardening practices and products that inhibit water movement within the soil (see earlier posts here, here, here, and here).

Science is not static however, and new research can change our understanding of soil-water relations. A new article was recently published in PLOS One that contradicts the well-established science about layered soils and other media impeding drainage. It’s important to give these contradictory viewpoints careful scrutiny before any deciding whether they represent a true paradigm shift or if they are fundamentally flawed. This article falls into the second category, primarily due to flawed experimental design.

The methods sections of scientific articles are, unfortunately, the least exciting. My approach to reading scientific articles is to read the abstract first and then the conclusion. (Kind of like having dessert before the salad course.) Then I read the introduction and discussion and finally the methods and results. Getting the big picture first prepares me for the nitty gritty details of how the work was done.

Red flags appeared as I read the introductory section: the author compared research on textural barriers between different soil types with their research, which was organic potting media overlaying drainage material. Differences in adjacent soil textures cause perched water tables, or as soil engineers like to call them, capillary barriers. Their presence is a well-established fact. But even given the faulty comparison there is substantial research showing that organic matter can also create capillary breaks with the underlying soil. This means there is a very large body of literature that supports the presence of capillary barriers between soils of different textures and between soils and other materials.

Eventually I got into the methods section. While reading about how to dissect methodology is not the most exciting thing in the world, learning how to do it is exciting – you never know what you will find. Ideally, methodological errors are found during peer review but sadly peer-review is not always of the highest quality. In any case, a careful reading of the methods section of this article generates more questions than it answers.

Without going into excruciating detail about experimental design (there are textbooks written on this), it’s important to understand what you will find in a rigorously designed experiment. There will be an underlying hypothesis (or research question) to explore, a well-designed experimental methodology with sufficient replicates and controls, and appropriate and objective statistical analyses. Paramount to all of this is that variability must be controlled, which means all replicates must be treated identically except for the variables being studied (in this case different drainage materials and their overlying potting media).

Below are many of the problems I identified, along with a brief explanation of why.

• “For trials with sand, a piece of fibreglass mesh (16 x 18 mesh count, approximately 1 mm spacing) was placed over the drainage hole to prevent the sand escaping.” Mesh should have been placed in ALL treatments, regardless if they were needed or not. The presence or absence of mesh has now become an uncontrolled variable (an unforced error to use sports terminology).
• “For each potting medium, trials were conducted with a layer of each drainage substrate to depths of 30 mm and 60 mm…” Weights of the materials (drainage as well as media) should have been made for each treatment replicate so that there are no differences in material weights among the replicates for each treatment. Each drainage substrate should then be shaken to eliminate any large gaps before adding the media on top. Differences in weights of the drainage material is another uncontrolled variable.
• “For each of the three potting media, a baseline moisture level was defined according to the mass of a fixed volume of medium.” These baseline moisture levels need to be reported in the methods. Furthermore, it would have been better to use fully hydrated media, as the wetting time for the different media were likely different.
• “Each filled container was irrigated from above using a watering can with a rose until the water level reached the top of the pot.” There should have been a fixed volume of water added to each container. Differences in how much water was added is another uncontrolled variable.
• “The containers were monitored until water was no longer visibly draining, which took between one minute and three hours.” The differences in time is another uncontrolled variable, as they do not appear to have been used in any of the data analysis. Among the questions one could ask is if there were differences in drainage times within the same treatment?
• “The saturating and draining process caused all the potting media to compact.”  Given that the media compacted to different levels, this introduces another uncontrolled variable. A fully hydrated media could have been compacted uniformly. Furthermore, adding water to a dry medium results in an unknown amount of water running down the inside of the plastic containers (which do not bind water), which is a loss unrelated to the experimental goal. Media hydration time varies among media. Unintended water loss is another uncontrolled variable.
• “The compacted depth was measured from one representative sample for each medium with each depth of drainage substrate…” This is a fatal methodological flaw. The depth should have been measured for each container and the average should have been calculated statistically. Furthermore, how was the “representative sample” chosen?

I did read the supplemental files (linked at the end of the article) which I hoped would contain much of the missing information I noted above. They did not – and again I had more questions arise than were answered.

The article was supposedly about drainage – and I expected there to be data generated that looked at drainage times and water loss. If a fixed volume of water was added to each container of fully hydrated substrate, it would have been easy to measure water loss over time. (You can do this at home using university extension information, such as this website from Iowa State University).  Instead, the article focuses on water holding capacity -which really doesn’t look at whether or not a perched water table exists -and on developing models.

If you’ve made it this far through my post, congratulations! Here are the takeaways:

• There were numerous design flaws and methodological errors, which introduced uncontrolled variables and created high levels of uncertainty. The data cannot be analyzed statistically and any discussion of the results is pointless.
• This is a good example of insufficient peer review. Had this been submitted to discipline-specific journal (like a journal in the soil or compost sciences), many of the problems I found would have been flagged. But the journal is a general interest journal, meaning that peer reviewers may have had little to no expertise with the science.

The cautionary tale here is don’t be a victim of SSS – single study syndrome. One contradictory article does not dismiss decades of peer-reviewed research and publications unless it meets a very high bar, which this one does not.