Having just seen a blog put together by a colleague I greatly respect outlining his thoughts and discoveries over the last 13 years, I felt this was a good as time as any to start one. Where to begin talking about pyroecophysiology? Although I have been working in fire science for over 20 years, let's start in 2016. This is when I pitched an idea in a comment paper where I outlined how we could conduct fire severity research differently. To provide some content. At the time, most fire severity studies would present observations of how fires affected some post-fire measure such as canopy cover, plant mortality, or soil impacts. They would often visit a fire after it occurred and often had never seen the site pre-fire. They would then use their best judgement to estimate how the fire had impacted the vegetation or soil at the site. They sometimes would use remote sensing imagery to also describe the effects of the fire. This imagery may have been collected between a week to a year after the fire. The temporal disconnects and unknowns always bothered me. There was a old phrase that always came to mind from the tv show "The West Wing". Namely, "post hoc ergo propter hoc" or 'after this, therefore because of this'. In ecology, this is often referred to as 'correlation, does not imply causation.' This phrase came to mind because there is often no pre-fire knowledge of the system, so all the effects that are assumed to be caused by the fire could be caused by a number of unknown factors that occurred before the fire. Likewise the temporal disconnect between the fire event and when the post-fire measures are collected was also a concern as many more factors could also interact to cause the observed effects. As I had written in an earlier paper in 2010, even if we can tease out that the fire caused the effect, the magnitude associated with just the fire remains unknown. This led me to pitch the ideas in the 2016 paper. Namely, could we explore the effects of fire on vegetation much like how scientists assess how pharmaceuticals impact living organisms: i.e. conduct 'dose-response' experiments. The idea was that known and repeatable quantities of heat from fires incident on plants would be the 'doses' and associated changes in physiology and morphology metrics or probability of mortality would be the 'responses'. Part of the idea was when fires impact humans, we know human's experience 1st, 2nd and 3rd degree burns and take longer to recover based on the degree of the burn. So why would this not be also true for fire impacting plants? We realized that we needed to explore this idea via controlled experiments. For the first experimental study, we grew saplings of both Larix occidentalis (western larch) and Pinus contorta (lodgepole pine). We had 28 of each and created 4 treatments. i.e. 7 of each species that we didn't burn. and 7 of each species that we burned at 3 different levels of heat incident from the fire. The measure of heat we settled on was fire radiative energy as we could reproduce the specific amount of heat released from known amounts of fuel that had a specific moisture content. Through this we had treatments of known heat, replicates of saplings, and unburned controls: the three essential elements of what we then described as pyroecophysiology research. What we found is that like fire impacting humans, increasing amounts of heat from fire on the tree species did lead to greater degrees of effects. Increasing the dose of heat incident on the saplings led to increased probability of mortality and in those that survived, the time to recovery and the magnitude of the post-fire impacts on future growth was increased with the greater doses of heat. The field of pyroecophysiology was born. Over the next 5 years we have continued to grow and burn more species to see if we can start understanding if and how these observations change in a wide variety of species that may have evolved better (or worse) to handle fires. We have also undertaken multiple studies looking at interactions between 'doses' of water stress (as a proxy for drought stress) and fire doses.
The term 'pyroecophysiology' has been picked up by others including a nice commentary by Daniel Johnson and Matt Jolly and the number of articles in this new field that connects heat transfer, fire ecology, and plant physiology have started to multiply. It is exciting time to see the start of something and I look forward to seeing how the field evolves as more research groups pursue pyroecophysiology research. For more reading of our works to date, check out the publication tab or follow these links: Smith et al. 2016 - The dose-response severity concept paper Sparks et al. 2016 - Study looking at long term impacts and monitoring with spectral indices Smith et al. 2017 - Results of dose-response experiments on Pinus contorta and Larix occidentalis Sparks et al. 2017 - Results of field-based dose-response experiments on mature Pinus ponderosa trees Sparks et al. 2018a - Impacts of fire and drought on Larix occidentalis Sparks et al. 2018b - Assessing dose-response relationships at landscape scales Smith et al. 2018 - Ideas paper presenting general model of flora, fauna, human responses to fire Steady et al. 2019 - Results of dose-response experiments on Pinus ponderosa Partelli-Feltrin et al. 2020 - Impacts of fire and drought on Pinus ponderosa Partelli-Feltrin et al. 2021 - Short and long term study on Pinus ponderosa with insights on mortality mechanisms Partelli-Feltrin et al. 2022 - Evaluated phloem dysfunction as a driver of fire-induced Pinus ponderosa mortality Wilson et al. 2022 - Impacts of fire intensity of Pinus palustris
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