Ruben E. Roos & Kristel van Zuijlen: different drivers for plants on mountain slopes

In harsh mountain conditions, what drivers affect alpine plant communities? And how do their traits change across a gradient? In this insight, Ruben E. Roos & Kristel van Zuijlen discuss their recent paper, Contrasting drivers of community‐level trait variation for vascular plants, lichens and bryophytes across an elevational gradient.

About the paper

Ruben and Kristel in the field
Ruben and Kristel in the field

What is the background behind your paper?

High up in the mountains, organisms have to deal with harsh physiological conditions, for example low temperatures, snow cover, and disturbances such as rock slides. The primary producers at high elevation have therefore adapted to deal with such conditions. However, alpine climate is changing, and this may impact the composition and functioning of alpine ecosystems. However, if we can understand how communities and their traits change across elevation gradients, we may use that knowledge to predict what communities will be present and how they will function under future climatic conditions.

What’s your paper about?

In our paper, we examined how functional traits of alpine plant communities change across an elevational gradient in an alpine landscape in Norway. We were particularly interested to know whether such changes are driven by species composition and/or intraspecific variation. Because alpine communities consist for a large part of lichens and bryophytes (mainly mosses) in addition to the more commonly studied vascular plants, we compared the functional trait responses to elevation for each of these three primary producer groups.

What are the key messages of your article?

We found that trait responses to elevation differed between functional traits, and between primary producer groups. Specifically, intraspecific variation was important for nutrient variables for vascular plants and lichens, but not for bryophytes. However, non-chemical traits and pH were mainly driven by changes in species composition (which we refer to as species turnover), for all three groups. For some traits, intraspecific variation was more important in lichens than in vascular plants and bryophytes, indicating that the lichens across our gradient show a great deal of intraspecific variation. Although we do not know if our results hold true across other elevational gradients, it suggests that the lichen community could be more resistant to climate change than the bryophyte and vascular plant community.

About the research

The Finse Alpine Research Center
The Finse Alpine Research Center

Why is it important and how does our paper contribute to the field?

Non-vascular primary producers are often overlooked in trait-based studies, even though they are almost always present. We don’t remember seeing a terrestrial ecosystem without lichens, mosses, liverworts, algae, etc. Maybe they aren’t included due to unfamiliarity with the species, or because we simply don’t know what traits to measure and how.

Our study is an important contribution to the trait literature, since it is the first study – as far as we know – comparing functional traits of three important primary producer groups across the same environmental gradient. We show that for some traits, vascular plants, lichens and bryophytes show similar responses, while for other traits, they may respond completely different. This indicates that it is important to include non-vascular groups in community-level trait studies, especially in places where they are important contributors to primary production and ecosystem processes, such as alpine environments. Further, our study shows that it is important to measure intraspecific variation, because it may be more important than changes in species composition for some traits.

What were the challenges while gathering your data?

Beforehand, we knew that it would be a lot of work to do the vegetation survey, harvesting and trait measurements, but we underestimated how much time it would take, especially sorting the material to species and measuring the traits. The further we went up in elevation, the smaller the plants and lichens are, and thus the longer we had to sort the biomass to gather enough material for measuring traits. In addition, we decided to measure SLA (specific leaf area) in bryophytes the same way as it is done for vascular plants, which is not an easy task since bryophyte “leaves” are often really tiny and fragile. Another challenge was the weather during field work. The Norwegian mountains are very rainy and windy. But with enough chocolate you can do anything!

About the authors

What are you currently working on?

Kristel – I am working on getting the other studies of my PhD project published. One of them is based on the same elevational gradient as the one we used for the Functional Ecology paper. For that study, we looked at decomposability of lichens and bryophytes across elevation, and how this is related to functional traits. For another study we set up a lichen transplant field experiment to study how different mat-forming lichens and their traits affect microclimate and decomposition.

Ruben – Just like Kristel, I have lot of data left from my PhD projects to work on. My focus will be on soil micro-arthropods; how their community composition and abundances change with elevation, their associations with lichens, and how they respond to and recover from experimental climate change. I’m very happy to be in a position where I can keep working on what I build up during my PhD, and try to get it all published of course.

What is the best thing about being an ecologist?

Ruben collecting trait material
Ruben collecting trait material

Kristel – What I like the most is trying to find out how plants (including mosses and lichens) can thrive under harsh environmental conditions, such as in alpine ecosystems, and how they in return affect their environment and ecosystem processes. This is especially relevant for mosses and lichens, since they often grow in places where vascular plants cannot persist. As a scientist, I like the combination of field and lab work, data analysis, and writing, and not having to do the same thing every day.

Ruben – I find inspiration in being outdoors, in the systems we study. I believe we sometimes sit in our offices too often, while we should be out in the world we try to understand. I also like going through the whole process of collecting data, lab work, statistics, and writing. I enjoy working at a university, and I think teaching is an important (and difficult, but fun) part of our job as ecologists. Where would we be without enthusiastic students?

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