In Insights we discover the story (and the people) behind a recent publication in Functional Ecology: what inspired the authors to do the research, how did the project develop and what wider impact might the work have?
In this week’s Insights, Tyler Refsland from the University of Illinois Urbana-Champaign, USA, talks about his paper titled: ‘Fire increases drought vulnerability of Quercus alba juveniles by altering forest microclimate and nitrogen availability’. Refsland and his colleague, Jennifer Fraterrigo present the results of an experiment where they imposed drought on natural and juvenile oak juvenile to disentangle the mechanisms underlying the effects of fire tree responses to drought. While postfire rerouting can temporarily improve water relations, fire exacerbates drought-driven declines in growth by both promoting a warmer microclimate and intensifying nitrogen limitation. Based on their results, Refsland & Fraterrigo postulate that the effect of fires ripple into the future by changing microclimate and resource condition, which could ultimately limit tree recruitment.
Your paper seems really timely, with Europe suffering from immense drought and reports of wildfires all across the globe. The message from your paper doesn’t seem to be good news for post-fire forest recovery, right?
Our study highlights that fire can have both positive and negative effects on the drought vulnerability of young trees, but that the negative effects prevail for small juveniles. An important caveat to emphasize here is that our study focused on post-fire recovery on the hottest and driest of landscape positions, upland south-facing slopes. Under the cooler and wetter conditions that characterize north-facing slopes, the effect of fire on drought vulnerability will likely be different. For example, fire intensity and thus its impact on forest structure and microclimate are all dependent on landscape context. Further research across a variety of post-fire environments is needed to better understand the generality of our findings.
Your research focusses on white oak, Quercus alba, which is a long-lived species. Do you think it could be possible to kick-start post-fire regeneration with a faster growing species that could improve microclimate and soil water relations, setting the stage for white oak?
Interesting idea. The light demands of eastern North American oak species such as Quercus alba, however, would make this difficult. White oaks do best under canopy gaps or exposed south-facing slopes where light levels are highest, rather than under the canopy of other species. At the same time, these local environments can be harsh in terms of air temperature and evapotranspiration. Oaks are generally well-adapted to these conditions, but our results show that drought in post-fire environments reduced leaf gas exchange rates and growth of small juvenile oaks.
If the prevalence of hotter and drier conditions increases in the future, I would expect the composition of oak species in this region to shift towards more drought tolerant oak species, such as post oak (Q. stellata), at the harshest sites and Q. alba to be restricted to wetter sites (north-facing slopes and lowland areas).
Can you briefly explain how your paper furthers our understanding of the functional ecology fire-impacted ecosystems?
I think among the most important findings of our paper is that repeat surface fires can alter the microclimate of relatively wet, eastern deciduous forests to such a degree that it can exacerbate drought stress in young trees. Furthermore, we find that surface fires may intensify nitrogen limitation for young trees during periods of drought. This suggests that for deep-rooted tree species (e.g. Quercus) that can access water even under severe drought, the assimilation and growth rates of young trees could instead be limited by nitrogen under the presence of fire and drought.
How has your career developed over the last few years?
Over the past couple of years, my research has slowly shifted away from lab and field-intensive work and towards meta-analysis and modelling projects. This fall, I’ll be starting a postdoc position at University of Nevada, Reno, where I hope to integrate field and modelling approaches to research drought mortality of western US tree species.
How do you balance work and downtime?
As a PhD candidate, I was NOT very successful at this! But as I wrapped up projects and finished my dissertation, I was finally able to dig myself out from the weeds and hit ‘reset’ on my personal and work life. In hindsight, I see just how critical it is to set firm expectations with your supervisor, colleagues and (most importantly) yourself concerning the hours you commit to work versus the rest of your life. This means you have to say ‘No’ quite frequently, and that’s okay.
What achievement are you most proud of?
One achievement I’m proud of is making the drought shelters for this study. Going in, I had no experience designing and making rainout shelters or throughfall structures. I think as scientists, we often find a lot of commonalities between the pleasures of research and the idea of engineering. That is until you attempt to solve an actual engineering problem and find yourself woefully naïve regarding the knowledge and skills it demands! Fortunately for me, my advisor and committee members helped me devise a plan for the rainout shelters that achieved our goals of being effective and mobile while not breaking the bank.
What do you like most about being an ecologist? What could you happily do without?
Like many ecologists, I really enjoy being in the field. This is especially true when research allows you to visit and explore amazing places you’ve never been. The obvious downside to being outside is dealing with pests and unpredictable weather. Southern Illinois, where this study took place, marks the confluence of the Mississippi and Ohio Rivers, as well as where North meets South in America. Working there as an ecologist, I saw the region in yet another way: as a major insect hub where southern (Lone Star tick, chiggers) and northern pests (Deer tick, mosquito) collaborate on your demise 😉
Can you recommend any interesting papers you’ve read lately?
I really enjoyed the paper by Alan Tepley and colleagues in the most recent Journal of Ecology that detailed the importance of fire-vegetation feedbacks in determining post-fire recovery of forests. The major take-home for me was that the impacts of climate change on future forest productivity will in part depend on the flammability of pioneer tree and shrub species characteristic of that region.
Read the paper in full here. You can read also the plain language summary: Hung out to dry: Fire can increase the vulnerability of young trees to drought on our summaries blog.