Very helpful pile of books on statistics
I am diving deep into the mysterious worlds of statistics to find my beautiful dataset the special analytic treatment it deserves. Luckily, I do not have to go alone on this adventure towards the very ends of statistical knowledge, there is a pile of helpful books to guide me on my quest.
And the internet, of course, the all-knowing internet, an endless source of answers.
To know what will happen to ecosystems in a changing world, we need to know the fate of the nutrients within them, like carbon and nitrogen.
As I don’t have pictures of the below-ground processes, I’ll stick to showing fungi, the brave and never failing helpers of decomposition. Pictures from Belgium.
To know the fate of these nutrients, we need to know how they are distributed and divided within such a system, and how the so-called nutrient cycles change in a warming climate.
This is not an easy task, as we miss a lot of information on many fundamental processes within these nutrient cycles, like the decomposition of dead plant parts (litter) in the soil and the release of nutrients from this soil.
We are now working towards a valuable addition to this field: we argue that soil litter decomposition is strongly related to the local climate (mainly temperature and precipitation), more than to biological factors like litter and soil type.
This is extremely useful, as it allows us to create easy and straightforward models to predict this litter decomposition.
We currently work on a paper presenting these models in Biogeoscience Discussions (Portillo-Estrada et al.), a new and open way of reviewing research. In this discussion section, it will be read by at least two reviewers, but also by everybody else interested, and all are invited to comment. Within some months, the discussion will be closed and the paper improved accordingly.
This is an exciting approach, as it means our research is already online and out there, and the whole community can help improving it.
I will keep you updated about the progress!
Reference
Portillo-Estrada et al. (under review). Biological and climatic controls on leaf litter decomposition across European forests and grasslands revealed by reciprocal litter transplantation experiments. Biogeosciences Discussion 12.
New paper published: Lembrechts, Milbau and Nijs (2015) AoB Plants.
Disturbance is important in ecology. It disrupts the status quo, improves the diversity, adds to the possibilities. It creates opportunities and disables others. As such, it is a driver of dynamics that is impossible to ignore.
Human disturbance in the mountains, Swedish Lapland
In most research, disturbance events are studied as a yes or no: the vegetation is either disturbed, or it is not. The origin and size of these disturbance events are then often varied (are we talking about grazing or complete vegetation removal, did the disturbance create gaps of a few centimeters or several meters, etc.). However, often neglected in these discussions is the fact that conditions within one such a disturbance event can vary considerably.
We argue in a recent paper in AoB Plants that vegetation gaps form a micro-ecosystem on their own, with large variation in conditions over not more than a few tens of centimeters. This variation occurs across the known variation on a macro-scale. We also argue that this small scale matters. It matters a lot, because plants colonising such gaps only experience the environment that is in their immediate surroundings, and they do not sense the conditions within the whole gap.
Temperature variation within disturbance events can vary over a scale of centimeters (National Park Hoge Kempen, Belgium)
Let us look at this concept with the help of a thought experiment. We travel to the mountains in a cold climate, where we will find a cold temperature gradient from ‘pretty fine’ in the lowlands to ‘unbearably cold’ at the highest elevations. We are lucky to have the Stress Gradient Hypothesis, a stronghold of ecology, to explain what will normally happen along such a gradient.
In a control system (without any disturbance), the interactions between species in the lowlands will be dominated by competition, a constant struggle to overthrown one’s neighbour and get (or maintain) access to life-defining resources. Towards higher elevations, on the other hand, there is another interaction that slowly gains importance: facilitation. The more stressful an environment becomes – in this case the colder it gets – the more a plant will benefit from a nearby colleague that can make this stress more bearable.
In stressful alpine environments, neighbours are often a blessing, Swedish Lapland
Vegetation is known to soften temperature extremes, providing important protection against freezing temperatures in a mountain environment, especially in the vulnerable early seedling stage.
Vegetation alters abiotic conditions on a small scale, Punta Arenas, Chile.
We can however imagine humans entering our peacefully imagined disturbance-free mountain ecosystems. They trample, they disturb, they create gaps. Open space, bare ground, fields of possibilities. But if we keep in mind the previously described Stress Gradient Hypothesis, we can imagine that our gap colonisers will now face a difficult dilemma: do they want to be close to the gap edge and their neighbours, or as far away from them as possible.
In the mild climate of the lowlands, the decision is easily made: there is not much good to be expected from the surrounding vegetation, they will just compete for light and nutrients and reduce your survival chances. The closer to the centre of the gap, the higher your chances get.
Predicted gap coloniser survival in mild (left) and stressful (right) environments, based on competition and facilitation
In the cold environment at high elevations, the dilemma gets a bit more complicated. Chances of surviving without help of a protective vegetation cover get lower, so the ideal location shifts towards the gap edge. Competition however keeps playing a role, so too close will still get you into trouble. The colder it gets, the more the balance will however shift towards the gap edge.
Final modeled coloniser survival in gaps along an elevation gradient, with a clear shift in the optimum (red) from the center of the gap to the gap edges
And all of this, my friends, is why the smallest scale matters: there is a strong gradient over which these biotic interactions weaken, and a coloniser will have the highest survival chance there were the trade-off results in an optimum.
On a mountain gradient, there are several factors that promote this gradual shift from gap center to gap edges. With increasing elevation, not only the temperature will get lower, the vegetation will also get smaller, shortening the distance over which competition and facilitation will be felt. The importance of facilitation will also increase, even more widening the difference in survival chances between gap edge and gap center.
But what does this mean? It means that at high elevations, gap colonisation will be strongly limited, as the only possible locations to colonise will be close to the gap edge, or in small gaps, while colonisers at low elevations will need larger gaps to stand a chance.
Non-native Achillea millefolium in the northern Scandes, Swedish Lapland
It will be important to keep this theory in mind and acknowledge the importance of the variation within disturbances when looking at several global change problems in mountains. For plant invasions in mountains, for example, disturbances have proven to be from major importance, as they are strongly connected to roads, paths, mountain huts etc. When they reach high elevations, however, this connection with anthropogenic disturbances might get lost, and the invaders might shift from roadsides to the natural vegetation. This shift from a limited number of locations of high disturbance to the vast area of less disturbed nature in mountains might make invasion management more challenging.
Disturbances like mountain roads serve as vectors for invading plants, Torres del Paine, Chile
From another perspective, the strong warming in alpine environments resulting from climate change will decrease the importance of facilitation at the expense of competition. Gap colonisers will then get opportunities to use a larger portion of gap surfaces, increasing the efficiency of gap regeneration and the succession rate in disturbed alpine environments. Increasing anthropogenic disturbance in mountains, in combination with climate change, might as such accelerate the observed upward movement of several species.
Experiments with small-scale disturbance in the mountains can shed light on the proposed patterns, Swedish Lapland
To summarise: as ecologists, we will need to dig deeper and look closer to find answers, even on the large scale of species distributions and movement. We will be surprised to find out how big our error has been until now.
Reference:
Good news for those ecologists studying species distributions: it turns out that the climatic niche of mountain plants is fairly conserved in space (Wasof et al. 2015).
Mountain avens, Dryas octopetala
These results come from a study on the distribution of alpine species in the European Alps and the northern Scandes, two mountain regions with very different characteristics but a significant overlap in species composition.
Orchid in the northern Scandes (Dactilorhiza majalis?)
The researchers compared the climatic niche of a large set of plant species that occurred in both mountain regions, and found that only a small percentage of these species experienced a regional effect on their niche. Especially species with disjunct populations (populations that are truly separated in space) showed high niche overlap, and the same was true for arctic-alpine species.
Dwarf birch, Betula nana
Although niches are in general surprisingly well conserved between the two regions, species occupy a wider range in the Alps than in the northern Scandes. More on the latter unexpected pattern in this informative post from Jonathan Lenoir, one of the authors.
Cloudberry, Rubus chamaemorus
Why do we care? Because the large and growing field of species distribution modelling has as one of its main assumptions that climatic niches are conservative. If they are not, any extrapolation of a limited geographic dataset to the total global distribution of a species would be invalid.
Hair’s tale cottongrass, Eriophorum vaginatum
Reference
Wasof et al. (2015) Disjunct populations of European vascular plant species keep the same climatic niches, Global Ecology and Biogeography, 24: 1401-1412.
Snowline wintergreen, Pyrola minor
On a misty autumn morning, while I was roaming through Flanders fields, I met some very fierce-looking sheep.
The look on their face, combined with the atmosphere created by the autumn fog, made me chuckle: they looked very smug and acted like the true definition of a badass.
‘Baby, don’t herd me, don’t herd me no more.’
And then I realised they deserved to have that look on their face, especially when viewed from my research’s point of view. For the plants in a grazed meadow, the grazers are their gods, and their hungry mouths define who will survive and who will not.
Grazers keep the vegetation short, and they create gaps with their hoofs. They keep the vegetation open as they prevent evolution towards the next successional stages, in which shrubs and trees inevitably take over. They thus provide good example of disturbance (an important part of my PhD, on which I will publish a paper soon).
Vegetation dominated by grazers will have a totally different species composition, where species that know how to handle these kinds of disturbances experience a strong advantage. Many grasses for example have their meristems (the important part of the plant where all growth is regulated) moved from the top of the plant to lower parts (in the nodes in the stem).
This means grazers (and the lawn mower for that matter) will mostly not hurt grasses that much, as they will only remove the replaceable parts of the plant and not the ‘expensive’ part that takes care of the growth.
At the moment, grazers have not been very well represented in my research, although reindeer are very important in our study system in the north of Sweden. The impressive looking sheep of the Belgian autumn however reminded me to keep the grazers and their important ecological role at least in mind.
Pictures taken in Boechout, Belgium
Scientific experiments take a long time. Before the very first meeting at which a research question is proposed and the publication of the final answer, there is a seemingly endless amount of intermittent steps (you can get an idea about all of them here).
For me as a PhD-student, I feel it is important to keep my vision clear along the long way. It might get misty between A and Z, with the final goal losing his clarity through countless practical questions along the way.
After almost three years, we now finally gathered all data for one of the main stories of my PhD, a story based on questions first posed by my supervisor and colleagues even before y PhD was in the picture.
Now we are almost three years later, and it is wise to admit that the original hypothesis might have been a little bit blurred over time. You all know the game of whispering a sentence from one person to another, where you end up with a totally different one after only a few trials, and there is a reason why nobody tries playing those games over a period of three years…
There is a chance that the true original hypothesis got lost in the mists of time: during the fieldwork, new questions arose that seemed more important, or the data analysis revealed other unexpected patterns that made you forget the first ideas.
While all these new questions are important when finalising a story, it is opportune to reach back to the very beginning and get a clear idea of what triggered all this work in the first place. Did we get an answer on the questions we first asked? Are these answers like we expected?
So that is what I did now, battling the fog and getting my head crystall clear, before I tackle this major question of my research. I am totally ready for it!
Pictures from Boechout, Belgium
The 3D lab 