Our May issue includes a new Special Feature: Facilitative mechanisms underlying the effects of biodiversity on ecosystem functioning. A photograph showcasing the experimental setup for one of the Special Feature articles also features on this month’s cover!

Here Guest Editor, author and cover photographer, Alexandra (Sasha) Wright & fellow Guest Editor, Ray Callaway, talk about the inspiration behind this Special Feature. You can also read their Editorial for this Special Feature, to find out more about the facilitative mechanisms that underlie positive biodiversity-ecosystem functioning relationships and for more details about all the articles included in this collection.

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Special Feature: Facilitative mechanisms underlying the effects of biodiversity on ecosystem functioning 

In September of 2019 I phoned Ray Callaway – “Ray I’m looking for more community-building in my professional life, do you have any advice?”

This conversation started what has become a multi-year effort to bring people together from around the world to focus on Biodiversity-Ecosystem Functioning (BEF) and traditional facilitation theory. In March of 2017 Ray and I finished working on a collaboration with Drs. Aurora Gaxiola and David Wardle. We published a paper (The overlooked role of facilitation in biodiversity experiments) where we put forth multiple hypotheses about the ways in which we thought facilitation might modify BEF relationships in different contexts. It was a completely remote New York/Montana/Singapore/Chile collaboration (back in the days before everything was a completely remote collaboration) that was wildly exciting and successful. We wanted to keep the momentum going.

The problem: Historically, BEF science is not well intertwined with facilitation science. This, of course, comes with some notable exceptions (Knops et al. 1999, Caldeira et al. 2001, Mulder et al. 2001, Schnitzer et al. 2011, Wright et al. 2015). As a result, the origins of BEF science have been deeply tied to competition theory and have often left facilitation as an afterthought. As BEF scientists began examining biodiversity questions through a lens of resource competition, overyielding, and Loreau and Hectors (LH) additive partitioning method (Loreau and Hector 2001); scientists that study facilitation focused on the relative interaction index (RII, Armas et al. 2004) and the stress gradient hypothesis (Callaway et al. 2002). The sub-disciplines were not far from each other, but in terms of shared vocabulary, experimental methods, and guiding theory, the two groups diverged.

As we move into a 2^nd or 3^rd generation of BEF science, we need all-hands-on-deck in terms of what expertise we bring to the table. Biodiversity continues to decline at unprecedented rates and this will likely come with a loss of some ecosystem functions upon which humans rely. But the mechanisms that explain the relationship between biodiversity loss and loss of ecosystem function remain poorly understood (particularly in some contexts).

The solution: As one step towards bridging this gap, we organized this special feature. We hoped to bring attention to some of the ways in which these fields are unique and thus could come together to create a shared vision that is greater than the sum of its parts. We are also in the process of organizing an in-person conference (that is currently indefinitely delayed) with Dr. Christian Schöb. If you are involved in research at the interface of BEF and facilitation we would love to hear from you! If you are a strict BEF theoretician or a strict facilitation theoretician who sees the value in this work, we also want to hear from you.

Images from Special Feature articles: (Left) Losapio et al. 2021 Photograph: Elizabeth Norton Hasday. (Centre) Cavieres, 2021 Photograph: Lohengrin A. Cavieres. (Right) Aguirre et al. 2021 Photograph: Alexandra Wright.

The special feature includes articles from multiple biodiversity experiments around the world (Jena Experiment in Germany and the Forest and Biodiversity experiment at Cedar Creek Ecosystem Science Reserve) as well as observational biodiversity gradients in drylands.  We discuss the role of the LH additive partition, calculating relative interaction indices, Grime’s humpbacked model, and network theory. The authors in the special feature explore multiple mechanisms of facilitation (microclimate amelioration, alleviation of photoinhibition, canopy structure effects on boundary layer conditions, enhanced nutrient/water supply, and higher order interactions with pests and soil organisms). We hope the special feature serves to inspire new directions for research and new collaborations across research groups!

Cover

The cover image shows an example of how we might reimagine our BEF experiments with mechanisms that are informed by facilitation theory, not just competition theory. The image shows an experiment that is highlighted in the Special Feature (Aguirre et al. 2021) wherein the authors manipulated humidity in an outdoor field experiment. The “fog” in the image is the humidity addition in an open-top chamber. The authors postulated that drought may drive more facilitation in higher diversity plant communities because these higher diversity communities can humidify the microclimate and alleviate high evaporative demand aboveground. In order to test this, the authors needed to manipulate evaporative demand (not just soil moisture). This led to the first manipulation of humidity in an outdoor field experiment in history. A great advance for multiple branches of ecology.

Sasha Wright California State University, USA
Ray Callaway University of Montana, USA

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You can read all the articles in our new Special Feature here: Facilitative mechanisms underlying the effects of biodiversity on ecosystem functioning

The article related to the cover image is “The experimental manipulation of atmospheric drought: Teasing out the role of microclimate in biodiversity experiments” by Aguirre, Hsieh, Watson & Wright.