Exotic plant species thrive at high(er) elevations

Sometimes one needs patience to answer a research question. Lots of it. The Mountain Invasion Research Network (MIREN) already asked itself this important question back in 2006: how fast are non-native species travelling uphill along mountain roads? Now it’s 2023, and for the first time we have an answer to this, thanks to long-term vegetation monitoring by a team of researchers across the globe, and the work of MIREN master-turned-PhD candidate Evelin Iseli, whose work now got published in Nature Ecology & Evolution (!). What follows is the English translation of the press release by our university. The paper itself can be found here!

Suppose you put your hiking boots in your backpack, fly to another continent and go hiking in the mountains. Chances are that you may find that seeds of local vegetation travelled the whole way with you in the mud on the soles of your shoes. If these fall off your shoe abroad, an alien plant may sprout where that seed has fallen. Thus, without realising it, you contribute to the spread of non-native plant species.

Moving uphill

Ecologists from the global MIREN-network found that the number of non-native plant species in mountain areas around the world has significantly increased in the past decade. Until now, alien plant species were advancing less in mountains compared to their increase at lower elevations. But due to climate warming on the one hand and increasing human influence at high elevations on the other, it now appears that non-native plants in mountains are also advancing steadily uphill.

The number of non-native species increased by 16% in mountain areas.

“Although the presence of native species in mountains is relatively well documented, long-term studies of alien species in mountain areas are very rare,” says Jonas Lembrechts, biologist at UAntwerpen. Lembrechts and his colleagues have therefore been monitoring non-native species along mountain roads since 2007, in 11 mountain areas around the world: in Norway, Switzerland, the Canary Islands, New South Wales, Victoria (Australia), central and southern Chile, India, Hawaii, Montana and Oregon.

“There are big differences in the speed of the invasion, but the general increase is unmistakable,” says Lembrechts. The study of the 11 mountain regions worldwide shows an increase in the number of alien species by as much as 16% over the past decade.

Mainly European plant species

Moreover, in 10 of the 11 regions studied, the scientists found the alien species at significantly higher altitudes than ten or even just five years ago. Moving to higher altitudes to follow their preferred climate is a well-known strategy for plants to defend themselves against climate change. Only, the rate at which alien species are climbing upwards is higher than if climate alone were the culprit.

“Europe is the largest exporter of exotic plants to mountainous regions worldwide, says Jonas Lembrechts. Left: Trifolium pratense from Western Europe in the Norwegian Scandes. Right: the European Taraxacum officinale in the Chilean mountains.

“Exotic species often enter new regions through the lowlands, where most of the people are,” says Lembrechts. “From there, they find their way to the mountains. But with a little help from humans, their spread can sometimes be lightning-fast, especially along mountain roads and trails.”

Off balance

Often these are then also European plant species, research shows. “Europe is currently by far the biggest exporter of exotic plants to mountain areas worldwide,” Lembrechts explains. “Not so strange, when you consider that in recent centuries it was also mainly Europeans who started visiting mountain areas on other continents, for tourist and commercial purposes.”

However, this is not good news. “Mountain nature is often very fragile,” says Lembrechts. “Alien plant species can threaten or drive out native species, which are important in the local ecosystem, throwing the system out of balance.”

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The mystery of the Dark and Light Beetles on Possession Island

New paper out! Espel, D.; Coux, C.; Pertierra, L.R.; Eymar-Dauphin, P.; Lembrechts, J.J.; Renault, D. Functional Niche Partitioning Occurs over Body Size but Not Nutrient Reserves nor Melanism in a Polar Carabid Beetle along an Altitudinal Gradient. Insects 2023, 14, 123.

The southern Indian Ocean is home to the little known archipelago of Crozet. Despite its harsh weather and lack of substantial human presence, the island is a haven for penguins and elephant seals. Among the island’s inhabitants is a seemingly ordinary beetle, the Amblystogenium pacificum. It crawls over and under the rocks, hunting for smaller things to eat, and just lives his normal beetly life. There is just one thing with this beetle that sparked the interest of the (unusually persistent colony of) French scientists on the island: there are two colour versions of it. A light and a dark one.

Star of the show: the endemic Carabid beetle Amblystogenium pacificum

Now, we wouldn’t be scientists if we didn’t want to dig deeper into this.

Scientists have proposed several hypotheses to explain this phenomenon, including Gloger’s rule, which states that darker coloration is a common response among insects exposed to cold conditions. If Gloger’s rule were at play, we would expect to see a fitness advantage in the darker insects when it’s colder. However, it’s rarely that simple in ecology. It’s worth noting that previous studies have observed that the proportion of dark beetles increases by about 8% for every 100 meters in altitude on the island. This results in a clear distinction in the spatial distribution of the two morphotypes. More recent observations made in fellfield habitats have reported that the proportion of brown to black beetles ranges from a 2:1 ratio of brown insects at low altitudes to a 2:1 ratio of black adults at higher altitudes. This further supports the idea that Gloger’s rule may be at play. But as scientists, we can never jump to conclusions too quickly, and we must always keep an open mind to other possibilities.

Find the beetle, happily running across a soft ‘moss forest’. Picture by Diane Espel

Nevertheless, there were both dark and light individuals across the entire elevation gradient on the island. This raises the question of whether the dark beetles fare better at higher elevations (in terms of being bigger, having more nutrient or lipid reserves, etc.) and vice versa.

However, there are other rules that come into play, such as Bergmann’s rule, which states that insects tend to get larger as the temperature gets colder. This is because larger body sizes in endothermic species often correspond to a smaller surface area to volume ratio and reduced heat dispersion in colder climates. Additionally, there is the rule of sexual size dimorphism, which states that female insects are typically larger than males.

So, how does all of this play out on our windy island? The good news is that the elevation (and thus climate) gradient is responsible for many trait differences among the beetles. However, it turns out that coloration does not seem to be a major factor in determining the performance of the beetles. Bergmann’s rule does appear to be at play, as elevation does seem to boost beetle body size (although at the very top of the mountain, the extremely harsh conditions have made them smaller again). Sexual dimorphism is also present, with females having more lipid and sugar reserves (which is pretty clever of them, if you ask me).

Body size as a function of altitude for dark (blue) versus light (green) male (dashed) versus female (full line) beetles. Elevation clearly affects body size, but with virtually no difference between the two colorations or even genders.

However, a so-called ‘functional hypervolume analysis’ did not show clear niche partitioning of the insects along the studied altitudinal gradient, and we had to conclude that niche partitioning was happening for body sizes rather than coloration types.

In conclusion, the mystery of the dark and light beetles on Crozet Island remains unsolved. The absence of clear patterns in the relationship between temperature and size highlights the complexity of the interactions between insects and their environment. Factors such as low temperatures and limited resources at higher altitudes likely play a role in shaping the beetles’ functional traits. But hey, isn’t that what science is all about? Asking questions and trying to find answers, even if they’re not always easy to come by. So let’s just say, the adventure continues!

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A robot as co-author

Ok, I’ll bite. The internet is literally full of fancy people jumping on the bandwagon called ‘ChatGPT’. The amount of lists I’ve seen floating by with ‘you are only using 1% of ChatGPTs full potential’ or ‘this is how I convinced the queen to marry me by using ChatGPT and so can you’ cannot be counted. But the thing is: we HAVE to talk about it. As this thing is a game changer (whether a big or a small game changer I leave open to discussion).

The potential applications for ChatGPT are numerous, but – let’s be honets – it’s important to acknowledge that it’s not as good as it looks for many questions you could ask it. Despite the opportunities it presents, there are also risks to consider. I have gained *some* insight on the tool and its appropriate usage now, and I wanted to share my perspective as an ecologist and lab leader.

First of all, it is important to note – as many have done before – that ChatGPT should not be used to write academic papers. Despite its ability to generate coherent introductions, deeper analysis of the text reveals a lack of credibility and depth. The tool lacks the capability to cite credible sources and often creates made-up papers as a result. It is thus unlikely that a thesis written by the robot would pass scrutiny: the introduction might sound good enough, but for the methods and results, and any depth in the discussion, they are still entirely on their own.

I know some of these people, but never ever have I published in Enviornmental Modelling & Software. So Veraverbeke, Bauwens & Muys, time to get writing!

Despite its limitations, ChatGPT can be a powerful tool when used correctly. Here are a few ways I have found it useful in my work:

  • Improve first drafts. Using ChatGPT to improve first drafts can be an effective way to save time and improve the overall quality of writing. By quickly jotting down ideas and creating a rough storyline, I can then feed this rough text through ChatGPT to improve sentence structure and coherence. This added step allows me to focus on refining and polishing the content, rather than spending time on correcting grammar and sentence flow. The ability to quickly identify and incorporate the good suggestions while discarding the bad ones, has significantly reduced the time and effort required to finalize my writing. Additionally, this approach ensures that the grammar and flow of sentences are already on point when I start polishing things myself, which ultimately leads to a polished and well-written final draft.
  • Ask it to change the tone of text. Why settle for plain and boring text when you can jazz it up with a little help from ChatGPT? By using it to change the tone of your text, you can add some pizzazz to your blog posts and tweets. ChatGPT can even serve as your personal brainstorming buddy, suggesting intriguing snippets of text and clever wordplay to make your writing more attractive. And while I can’t say I use the final version it proposes, I do like to sneakily steal a few improvements here and there. So next time you’re struggling to add a touch of personality to your writing, don’t be afraid to turn to ChatGPT for a little inspiration. (Ok, I admit, all the witty wordplay is entirely ChatGPTs-doing, this paragraph was significantly more boring!)
  • Shortening texts: I asked ChatGPT to suggest how to shorten a project proposal from 8 to 4 pages. It came up with great suggestions to regroup or rewrite sentences in a more compact way, which also helps with email writing and other types of writing that need to be concise.
  • Annotate R-code. This is a relatively new discovery for me, but I think it will be a GREAT tool for my students! I just feed in a piece of R-code and ask it to annotate it, and it writes down in text what all the steps mean. For students, who are often unfamiliar with many of the tips and tricks of R that I learned over the years, this can make R-code I sent them a lot easier to understand.
  • Suggesting formatting for things I am not familiar with writing: For example, I haven’t written too many recommendation letters yet, so I ask ChatGPT for an example by feeding it some keywords for the candidate in question. This gets rid of the ’empty page’-issue where you don’t know how to start writing and lets you build on a good foundation.

My final words are perhaps the most important part of this blogpost: we HAVE to discuss this tool with our students. They are more tech-savvy then we are, so they will find out about it. Yet they might not get all the pro’s and cons, and they might especially brush over the ethics. Can they use it? Sure, I’m all in favour of getting all the help one can, the main goal of their work (in their master or PhD thesis, mind you, not in other courses) in my opinion is anyway to advance science and grow as a human in the process. They can use whatever tool they want, be it a fancy and expensive measurement tool or a chatty robot. As long as they know the strengths and weaknesses. That’s the same for that fancy measurement tool for that matter.

It’s a common question – is the text I’ve written still mine when I’ve utilized a language model like ChatGPT? I firmly believe it is. While the model may offer suggestions, I ultimately have the final say on what to include or not. Think of it as having a co-author, one who carefully reads and offers suggestions, but it’s ultimately up to me to decide what makes the final cut.

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Database progress

Last week, we bid farewell to Amber, a bittersweet goodbye that marks the end of a successful chapter in our ‘SoilTemp’ project. Yet it also provides closure to a very good story, as you’ll see.

Amber joined us as a master’s student and wrote an outstanding thesis on the air conditioning effect of nature in gardens, in the framework of our ‘CurieuzeNeuzen’ citizen science project. She then joined us part-time as a database manager for the SoilTemp database, and our achievements together during that time were nothing short of fabulous.

So how did we get Amber on board? After getting a few grant rejections, I sent out a tweet in desperation, warning the community that our planned work with SoilTemp was in jeopardy. But as fate would have it, the community rallied around us! GEO Mountains, an initiative focused on global environmental monitoring in mountains, for example, offered a concrete solution that resulted in this part-time job for Amber. Our main goals were two-fold: to make significant strides towards open access publication of the SoilTemp database and to increase its coverage in mountain regions worldwide, particularly in those hard-to-reach areas where even weather stations are scarce.

Sensor installed in my own favourite cold-climate mountain region in the northern Scandes, where it monitors birch forest understory temperature in a dense field of Empetrum and Vaccinium heathland

Amber sailed through the backlog of data submissions like a database diva and reprocessed all 35,000 time series in a format that will allow them to be entered into our upcoming relational database. The latter is being accomplished together with Rémy from iDiv (Germany), another epic story for another day. And our second goal? A mountain of success. We equipped a whole lot of regions participating in the Mountain Invasion Research Network (MIREN) with sensors, and we’re seeing increasing monitoring in many cold-climate mountains, tropical mountains, and especially African regions. The large white gaps on our map are shrinking fast!

So, thanks Amber, and thanks GEO-Mountains, we definitely made the best of it!

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Battling my emails

I started tracking my time at work in detail at the start of my postdoc in 2018, using the amazing app ‘Timeular’. This series of stories provides some insights into postdoc life using that data.

A traumatizing aspect of academia to many post-PhD scientists, perhaps: the inbox! Throughout my postdoc career, I noticed soon enough that the tide of emails was swelling, especially from the moment – in 2019 – that I put myself at the steering wheel of SoilTemp, a network of several hundred scientists. An increasingly international network with increasingly many collaborations, and you can imagine how many emails would come in! Yet, how much of my time was actually going into emailing?

Numbers, please!

Percentage of my time spent emailing since the start of my postdoc in 2018, tracked minutiously using the Timeular tracking software.

At the start of my postdoc, the mailbox (and its fancy relatives like Slack, Microsoft Teams, or even Facebook Messenger for some colleagues) only ate up a blissful 7% of my time. By 2020, with SoilTemp in full swing, I rounded the magical number of 20%. In a 5-day week, that’s one full day of emailing… Daunting! And no wonder I started to consider my efficacy.

If that amount of emailing is truly problematic, that’s a different story, of course. Not only was I managing this large network with its seas of useful and important emails, a lot of my other tasks were also increasingly replaced by an advisory role. Statistical analyses and paper writing as done in my PhD and at the start of my postdoc was now turning into assisting students or colleagues to do just that. Many of their questions could often be answered in a short – or longer – email, and them taking over lead authorship on many papers implied that my own time spent on these papers was reducing.

Nevertheless, I was realizing that I needed to be smart and efficient to keep that tide of emails at bay. I decided to step away from the immediate answering that I was used to from back in the days and delineated specific moments in which I would email. Now, I’m starting my Monday, Wednesday and Friday by working through my inbox and putting it back to zero. I answer emails that only take me up to 10 minutes of work, and schedule more demanding ones for different times, depending on their deadline.

This way, I am usually relatively fast with my response (2 days maximum), while still keeping a significant chunk of my week email-free. I do make an exception for my students, of course: their questions, thoughts, musings, or whatever they feel the need to share, will usually get a much quicker, if not immediate, response (as long as I can answer in less than 5 minutes).

Is this strategy paying off? I bet you it is! I regained some sanity, I am still on top of my inbox, and I turned the tide of emails: in 2022, the percentage was down to 14.5%, a more than 5% drop since 2020! Very happy the numbers support that decision!

Microsoft Teams – and the IT support team asleep next to it
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Hitchhiking mountain roads and trails

The Mountain Invasion Research Network (MIREN) has made itself ‘world famous’ through its protocol for the long-term monitoring of vegetation along mountain roads. We even got a recent publication dedicated in its entirety to that protocol! However, mountains – and the rest of our increasingly connected world, for that matter – are crisscrossed by a whole bunch of other ‘linear disturbances’. An obvious question thus arose: are the vegetation patterns we see along roads mirrored along these other linear disturbances, such as trails?

How problematic to nature are mountain trails – linear disturbances that protrude deep into our most precious protected nature.

To answer that question, we set up a second global vegetation monitoring protocol, yet now focussed on mountain trailsides. While our roadside protocol has been adopted in more than twenty regions worldwide, the tally for the trail protocol is currently at six. So a tad more humble in its scope, yet still more than enough to satisfactorily answer a first important general question – at the core of our MIREN business: are patterns in non-native species richness along mountain trails a mirror of those found along mountain roads?

Hiking along mountain trails can bring non-native species to surprisingly high elevations. In this stony desert above the treeline in the Chilean Andes, we found some European Taraxacum flowers!

The answer can be found in a recent publication – part of a new book on the role of tourism and recreation as drivers of biological invasions.

So how do our trails compare? Observed levels of plant invasion were substantially lower along trails than along roads, adding up to only about 20% of the species numbers. Nevertheless, the same decline in richness with elevation is found that is so characteristic of mountain roadsides across the globe, and many of the most common non-native plant species along roads are also found along trails.

Most striking, however, is the lack of decline in non-native species richness with distance to the disturbance. Along roads, we see worldwide the same characteristic pattern, with high numbers of non-natives in roadsides and then a more or less steep drop in species close to the road in the interior vegetation. Along trails, this pattern is virtually not there, which implies that levels of invasion are largely the same in trailsides and the interior vegetation.

Non-native species richness along mountain trails (red line) and in the adjacent natural vegetation (turquoise line) across six mountain regions (see map). Yellow-to-brown ‘smudges’ on the map depict the global mountain regions.

The latter has some worrisome implications, as it shows that the resistance to invasion of the interior vegetation close to trails is much lower than along roads. This could be due to the sparser vegetation (most studied trails were at higher elevations in the mountains than the roads), but most likely also to the differences in disturbance dynamics: while roadsides are often highly disturbed close to the road, trailsides are less disturbed in general, yet the ‘disturbers’ often wander off the trail more, spreading its impact further into the interior vegetation.

European dandelion in the alpine zone of the Chilean Andes

The results of our first global comparative analysis of roads and trails are thus both encouraging and worrying. Encouraging for our trailside managers is the fact that levels of invasion are lower here than along roads. Nevertheless, the lower resistance against invasion of the surroundings asks for strong preventive action to limit the impact of invasions along mountain trails, especially those in vulnerable protected areas.


Barros et al. (2022). The Role of Roads and Trails for Facilitating Mountain Plant Invasions. https://doi.org/10.1079/9781800620544.000. Full text here!

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