A little walk

Winter - 1

Rainy weather and thesis writing joined forces to lock me up inside a bit more than I would like in the first months of 2018, yet that is a pattern that I am determined to break.

Winter - 3

Because what is nicer than a stroll through a sun-blazed world? We did get lucky recently with some beautiful winter weather, in anticipation of what I strongly believe to become a perfect spring.

Winter - 7

Next week, I will exchange the cold weather for the soft Mediterranean spring of Portugal, where I will be joining a meeting of the International Biogeographic Society, to discuss the recent state of our knowledge on species distributions.

Winter - 8

No complaints about the beautiful nature of Flanders, but a bit of the Iberian peninsula will not hurt either, I suppose, so I hope I can soon offer you all some more exotic pictures and stories than those in this post.

Winter - 6

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Lagging behind

Species have been reported to be moving poleward and upward in mountains as a result of climate change. Evidence of this movement is piling up rapidly, and with every passing year the increasing speed at which species are moving up- and poleward is becoming ever so visible. Yet new studies also reveal that this species movement is often not as straightforward as it looks at first sight.

Indeed, one might think: climate warms, so species will follow. The problem is, however, that a species’ reaction to a change in their environment is not always that fast. They often need some time to adjust and move towards where climate is now suitable. This delayed reaction is especially true for sessile species, like plants, that depend almost entirely on seed transportation to travel around.


Plants and other sessile organism often show a delayed response to climate change. (Northern Scandes, Norway)

These so-called lags in species distribution shifts are currently not well understood, and even less well accounted for in our predictions of species distributions for the coming centuries. Which is why the recent review paper (Alexander et al., 2017, arising from a workshop organized by the Mountain Invasion Research Network) provides such timely steps forward for our understanding of these lags.

The paper distinguishes three different types of lags: “dispersal lags” indicate that a species has trouble to spread to higher elevations or towards the poles at the pace of the changing climate, while “establishment lags” result from problems with getting a foothold after arriving in a new environment. The last type of lag, called “extinction lags”, indicate that a species fails to disappear from an environment that might have become inhabitable.


Species often show an extinction lag, surviving for a certain time in an averse environment until time catches up with it. (Yellowstone National Park, USA)

Establishment and extinction lags seem to play a crucial role in shaping species distributions in this dynamic world. For example, closed vegetation in arctic/alpine ecosystems turns out to be very resistant to establishment of upward moving plants species. Thus even when low elevation species arrive at higher elevations, they often find a highly resistant native vegetation that is hard to overtake.  At the same time, many species seem to persist at their lower range edge, even through substantial climatic changes. Again, biotic interactions are likely at play, which are said to be more important than climate at the lower range edge of species.


Alpine species can often survive in areas at their warmer range edge if they are spared from competition with fast-growing species. (Yellowstone National Park, USA)

We humans play a critical role here as well. Surprisingly often, human influence is seen to reduce lags in distribution shifts: humans help with transportation of species to colder environments, for example through seeds sticking to clothing, and as such reduce the dispersal lag. Anthropogenic disturbance will reduce the resistance of the receiving community at high elevations as well, making establishment a lot easier for newcomers and thus reducing the establishment lag. Finally, these new invaders might indirectly reduce the extinction lag by outcompeting the native community, forcing them to retreat upward.


Humans can transport species to colder environments  via roads, and as such help them to better track climate change. (Northern Scandes, Norway)

So why do we care about these lags? Well, they are critical to understand what will happen to our nature in the coming years, with increased climate warming and unlikely-to-cease anthropogenic disturbances looming at the horizon. Ecosystems are already seen to be changing drastically, with novel communities sprouting up of species that might have never lived together before. Yet as species are likely to be lagging behind to these changing in their environment, much more change might still be on the way. For a species, lagging behind climate change might indicate an inability to keep up with the changes. Good dispersers, on the other hand, might easily be able to track the climate, only to find the novel communties they enter to lack the species they usually interact with and desperately need to survive.

Further reading:

Alexander et al. (2018) Lags in the response of mountain plant communities to climate change. Global Change Biology 24(2): 563–579.



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The season of anticipation

Winter - 6

We passed that time of year again. That moment just before spring breaks loose, when king winter gives you one last wack around the ears before hurrying back to its royal halls above the polar circle. We had a serious ‘season of anticipation’ here in Belgium last week – as I like to call it, with an extreme polar vortex driving freezing colds and even a bit of snow. Just when our little plant-friends everywhere were making the last preparations for spring.

Winter - 1 (1)

And that makes this season of anticipation a tricky balancing act. Plants everywhere are already in full anticipation of spring, but climate change is causing many species to bud earlier and earlier in the season. That in itself is not that much of a problem, tracking climate change is supposedly the best way for an organism to deal with it. A new study in Nature Communications has however shown that this warming climate might – contradictory enough – increase the frost damage experienced by these budding plants.

Winter - 1

Indeed, the warming climate does not necessarily reduce freezing spells at the end of winter or in early spring, with perhaps an important role for the increase of extreme events as a result of climate change as well. The authors – of which some of our own Global Change Ecology center – even showed an increase in frost days during the growing season for many species on the northern Hemisphere, and that especially in those regions that are shown to be heating up the most.

Winter - 3

The season of anticipation is thus most of all a season of balancing. While many of the earliest budding plant species are evolved to deal with a bit of early-season uncertainty, too much change might very well get them in trouble.


Liu et al. (2018) Extension of the growing season increases vegetation exposure to frost. Nature Communications 9:426.

Winter - 5

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Our paper in Oikos

Our latest paper on species evenness in diversity experiments is now officially published as Editor’s Choice in the March issue of Oikos! Good news for you, as that means the paper is now available open access. Find it here!


Want to have a summary of what this paper was about? Check back my earlier blogpost about it.

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There it is! The fruit of hard labour, the harvest of what has been sown 5 years ago: the draft of my PhD-thesis!

It is out of my hands now, while the jury is bowing their wise heads over it. But oh does it feel nice! To see these thoughts on paper, all neatly written down; the best thoughts of me and so many of my fine colleagues, on my favourite topic in the world.


Now on to the next steps: the bullet list for my PhD is finally getting alarmingly much shorter than it ever was. Pre-defense, re-writing, finalizing and defending, that is all there is left. But do not panic, the bullet list for the future is already put in position, I am unlikely to end up bored!

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Species distributions in a messy world

At the meeting in Zurich (introduced here for those who missed it), species distribution ecologists (like me) and people from the remote sensing community came together to meet. Troughout the discussions we had, an intriguing conclusion surfaced that I found worth mentioning here. To state it boldly: humans are making a mess of species distributions.

To take you back to the theory: where in the world we find a species, is to a large degree defined by its climatic niche, which is the set of environmental conditions in which the species can survive. Is a place too cold or too hot, too dry or too wet, then the species will not be there. Every species has different wishes in that regard, yet all of them have limits. That is what we call the fundamental niche.

There is however something else that defines where in the world will find our species in the end: other species. The interactions with other organisms will work on top of and in interaction with the environmental conditions in defining the so-called realized niche, which is usually only a part of the fundamental niche. For example, alpine plant species might be able to handle the milder climate of a valley, yet they are outcompeted there by other plant species that grow much faster and leave no space for these slow-growing little creatures. If you would give them a helping hand, by planting them in a rock garden, for example, they happily illustrate you how much broader their fundamental niche is.


An alpine species like this Saxifraga can survive and grow in harsh environments

Now there is one organism with a disproportionally huge influence on these realized niches: humans. Like no other species, we influence the landscape, change the land cover, disturb the environment. And inevitably, species are going to appear or disappear following these changes: they might avoid – or not – urban environments, benefit from the edges of fragmented forest patches, or a myriad of other negative ànd positive reactions to all these anthropogenic influences.


Agricultural land looks in no regard like the natural environment that would have been here without human influence.

If one now wants to model where a species actually is (i.e. its realized distribution, an important goal of a lot of our work here on plants), it is obviously crucial to take that human component into account. This is however rarely done, expect for local, regional trials. Most large-scale assessments still focus largely on the abiotic environment, and you can easily see how untrustworthy such predictions would be. The problem is that the human influence on the landscape results in highly heterogeneous conditions, with a lot of variation on a very small scale. And to get good and accurate information on this messy world of humans, is complicated.


Cities, like Mechelen (Belgium) here on the picture, are good for a very heterogeneous environment, due to the wide variety of structures, surfaces, and human disturbances on a small area.

Yet times are a-changing. Recent years have seen an increasing availability of highly accurate data on human land use and the accompanying land cover, thanks to rapidly developing remote sensing techniques: satellite images are improving with every launch, drones are becoming more accessible, and the accuracy of our species distribution models is rapidly following.

So yes, humans are messing with species distributions, yet by joining forces between distribution ecologists and remote sensers, we will now soon be able to assess accurately how bad this is for our species.

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This week brought us to Zürich, the magnificent city of bank buildings and rösti. We were heading for a highly interesting meeting, organised by the GMBA, the Global Mountain Biodiversity Assessment. They gathered a team of leading scientists from two different disciplines: ecology and remote sensing.

Ecologists, like I am one, are interested in the distribution of species. To understand these distributions, we need detailed information of the environment in which the species are living. The remote sensing community on the other hand uses drones, airplanes or even satellites to monitor the environment with extremely high detail.

Aha, you might say, sounds like you two are made for eachother! Yes, indeed. Yet as often, one community does not really know what the other has to offer, while the other is not entirely sure what the one community needs. This meeting tried to bridge that gap, on the one hand show ecologists which remote sensing techniques are ready to use, and what to expect in the near future, and on the other hand let us ecologists make up our mind on what we would like to get next from remote sensing.

And all that was a tremenduous success in my opinion. What a promising field is this remote sensing! You will definitely hear more on this later!


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