Tag Archives: moose

Cool As A Moose?

Guest post by Katariina Vuorinen

Cool as a moose: How can browsing counteract climate warming effects across boreal forest ecosystems? (2020) Vuorinen et al., Ecology, https://doi.org/10.1002/ecy.3159

The Crux

When temperatures increase, trees grow more. When a moose struts in and eats the twigs, trees grow less. So, if we just have enough moose around, climate warming won’t be able to increase the growth rate of trees. This is what we call the “cooling” effect. Rather simple – and cool – story, right?

However, every ecologist knows that the biological theatre is more complex than this. What if snow protects saplings against browsing? What if changes in temperature affect moose in such a way that they will not feed on trees in the same way as they used to? What if trees’ response to moose is actually different depending on whether it is warm or cold? In complex ecological systems, tree growth is determined in an intricate network of interactions, where the story line is so mind-bogglingly complicated that it seems almost impossible to say what is actually going on.

Luckily, it’s not quite impossible. In this paper, we set out to model those intricate networks, taking into account everything from the climate, the tree species, the effect of time, to the presence of herbivores and their browsing intensity, in an attempt to disentangle that complex biological theatre.

What We Did

To get a baseline impression of what happens to trees when moose aren’t around, we set up fences to keep the voracious ungulates away. Originally, this fencing was started by NTNU University Museum in Trøndelag, later expanding to 62 sites scattered across Norway and eastern Canada. As moose can only browse on relatively small trees, fences were placed in clear-cut areas where we could monitor the growth of the trees from the sapling phase.

After keeping track of the height of hundreds of trees inside and outside of the fences for more than a decade, we had assembled over 16 000 growth measurements. These were accompanied by annual estimations of the proportion of browsed twigs. Based on existing knowledge about which plant species the moose preferred, we also estimated the amount of food available for moose at each site. The tree growth and browsing data were complemented with data on three climatic variables, namely, growth period temperature, precipitation and winter snow-water equivalent, as well as data on regional moose density.

To grow or not to grow: for a rowan or a birch, a protective fence (on the left side in the photo) might be a matter of life and dead (Image credit: Katariina E. M. Vuorinen, CC BY 2.0)

We analyzed the data with structural equation models (SEMs) that combine multiple predictors and response variables into one big model network. A SEM allows you to treat an environmental variable both as an explanatory variable and a response variable simultaneously. For instance, the amount of competing trees could be explained by moose presence, but it itself could explain tree growth.

Did You Know

Herbivore cooling effects are better documented in arctic and alpine systems, where smaller woody plants namely shrubs, play the role of the trees. Empirical studies have shown that for example reindeer can slow down climate-change driven shrubification that would otherwise result in loss of open tundra. However, also in the arctic, herbivore effects take multiple forms: sheep effect seem to be modified by climate, potentially via plant-plant competition.

What We Found

Three of the studied tree species played along with the simple cooling story: Canadian rowan and birch and Norwegian birch. They benefited from higher temperatures and suffered from moose. However, most of the tree species wrote their own, more nuanced narratives. Canadian fir responded more weakly to temperature when moose were missing. Norwegian rowan flipped its temperature response curve around if moose were present. Norwegian pine responded negatively to temperature, but did not seem to be bothered by moose. This is understandable, as heat turns into an enemy when it gets too hot. The soft, palatable species took more damage from moose than spiky spruce and pine.

From a tree’s point of view, the role of a moose can change from a foe to a friend if the moose browses on a neighbouring competitor tree. Canadian fir and rowan and Norwegian birch and pine benefited from the fact that moose lowered the growth of competing trees. Snow complicated the story even further. Norwegian rowan benefited from increasing winter precipitation, but only outside of the fences, suggesting that individual trees were indeed protected from browsing by a snow layer. This is potentially a result of snow lowering the proportion of browsed twigs. Interestingly, also temperature affected browsing intensity, but the effect size and direction varied between different tree species.

The bottom line given by these results is clear: the moose cooling effect exists, but how important it is really depends on ecological context.


We always need to careful when assessing results obtained by using datasets of different accuracies. Where locally estimated browsing data was highly precise, regional moose density and climate data were less so. Thus, the effect strengths may partly reflect differences in data quality rather than true differences between explanatory variables. Overcoming these weaknesses might reveal side-plots yet to be unravelled.

So What?

So, if the pathways of climate effects are this complex, what is actually going to happen in the boreal forests when temperatures rise? Some tree species may benefit from increase of temperature just to end up on the moose dinner menu. Less tasty ones may thrive, or suffer from excess heat and increased competition. If global warming brings us snowless springs, cooling potential of browsing may increase. In contrast, if we get more snow with increasing precipitation, moose may turn into a trivial side-character.

In the complex interplay of biotic and abiotic actors, only one thing is certain: that we do not know what will happen outside the observed variable boundaries. Interactions and non-linearities make any future predictions highly uncertain. If we are to place hope on herbivory as a cooler of climate change impacts, constraints imposed by species differences, snow, competition, as well as climate effects on browsing must be acknowledged – not so neat of a story, and perhaps less cool, but nearer the ecological reality.

Katariina E. M. Vuorinen is a PhD candidate at the Norwegian University of Science and Technology. She studies the effects of climate and large herbivores on plants by using data from across boreal and arctic biomes. You can read more about her work at this link.

Title Image Credit: James D. M. Speed, NTNU University Museum, CC BY 2.0, Image Cropped

On Moose Who Reproduce: To Use Or Not To Use

Guest post by Endre Grüner Ofstad

Opposing fitness consequences of habitat use in a harvested moose population (2019) Ofstad, Markussen at al., Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.13221

The Crux

At the heart of our understanding of animal behaviour is Optimal Foraging Theory. It’s related to the core concepts of population ecology, and essentially asks which life history trait a species is more concerned with – survival or reproduction. For instance, often for a herbivore, the areas where they will find the most food is also the area where the most predators will be lurking. This presents them with two options – eat lots, reproduce a lot, and die young, or eat less, reproduce less (at least per year) and live longer.

On a species level we can compare mice and elephants. Yet these differences also occur within species and populations. Some individuals are more prone to high-risk strategies, while others prefer the low-risk strategy. Which strategy is the best will depend on the prevailing environment. For instance, a situation with few predators (or hunters) will favour the more risk-prone strategy, while a strong presence of predators will favour the risk-averse strategy. Populations who experience environmental variations are expected to have a composition of strategies that varies accordingly. 

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10 Great (And Not-So Great) Social Distancers of the Animal Kingdom

In the time of a global crisis like the one we’re in now, it’s more important than ever that we pay attention to what scientists are saying.

However, my colleagues and I are ecologists, and as such don’t really have as much practical advice for you as epidemiologists and sociologists do right now. All we can really say is stay at home, and practice physical distancing (NOT social distancing, we need each other more than ever right now).

However not all species have the comfort of being social without being close to each other. So in the name of providing some entertainment in difficult times, I gathered a bunch of colleagues together to figure out how some of their study organisms would cope if the need to socially distance was imposed on them.

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Can Humans and Wild Ungulates Live Together in a European Landscape?

Guest post by Benjamin Cretois (Image Credit: Wer Mei, CC BY 2.0)

The challenges and opportunities of coexisting with wild ungulates in the human-dominated landscapes of Europe’s Anthropocene (2020) Linnell, Cretois et al., Biological Conservation, https://doi.org/10.1016/j.biocon.2020.108500

The Crux

The “land sparing vs land sharing” debate is not new to wildlife conservation and is more relevant now than ever. Land sparing entails creating areas distinctly for wildlife, commonly referred to as Protected Areas. The science of spared landscape is well developed and its principles were fundamental to early conservation biology. On the other hand, the confinement of wildlife into human-free area is possible on a very limited in a highly anthropogenic landscape like Europe. Hence, the coexistence movement, which requires both wildlife and humans to share their landscape, leading to a wide range of interactions between the too. This is especially true when it comes to charismatic large mammals including large carnivores and ungulates, whose range has large overlaps with ours.

We wanted to summarise the knowledge on wild ungulate distributions and examine wild ungulate-human interactions. Ungulates are quite varied in Europe, and this study included species such as the wild boar, European bison, moose and roe deer.

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Fredrik Widemo: The Manifold Conflicts Behind the Hunting Industry

Image Credit: USFWS Endangered Species, CC BY 2.0, Image Cropped

Rewilding is a tricky business. Bringing back species that once roamed a country as their native land may seem like a worthy cause, but it is often fraught with conflict. People don’t want predators threatening their safety, or herbivores destroying their crops. Rural vs. urban tensions come into play. Local and federal politics get thrown into the mix.

With that in mind, I sat down with Associate Professor Fredrik Widemo, currently a Senior lecturer with the Swedish University of Agricultural Sciences. Fredrik has previously worked at both the Swedish Association for Hunting and Wildlife Management (where he was the Director of Science) and the Swedish Biodiversity Centre. We explored some of the complexities behind the rewilding of wolves and its effects on the hunting and forestry industries in Sweden.

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Ecology of a Forest God

Image Credit: The Ritual, 2017

In our discussion of 2017’s The Ritual, we stumble through a large confusing forest riddled with large spinous processes and patches of burnt skin. Should you hang a corpse up in your front garden? Probably not. Not good for the soil.

00:28 – SciComm & the Insect Apolcalypse
07:16 – The Norse Gods in Cinema
15:04 – Ecology of the Forest God
43:43 – The Forest God v. Beowulf

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