Province of Lleida, Catalonia, Spain (Image Credit: Julia Ramsauer, CC BY 2.0, Image Cropped)

As carbon emissions rise globally, finding ways to reduce emissions and store carbon are coming to the forefront of modern science. Forests are huge carbon stores thanks to the copious amount of photosynthesis they conduct. As climate change increases temperatures, trees become a very important tool in the fight against rising emissions. One study even described forest restoration overwhelmingly more powerful than all other proposed climate change solutions. You might think: “So let’s go and plant trees!” Unfortunately, it’s not so easy.

Trees themselves will struggle with the changing climate. Depending on the tree species, they are adapted to specific physiological balances, especially of air (i.e. temperature) and water (i.e. precipitation). When these balances change, as is to be expected in the course of climate change, the persistence of single trees and even whole forest ecosystems will be threatened.

This means that important decisions about where to plant trees and which kind of species will have to be made. So let’s take a broad look at the future of forests, specifically those in Europe. I’ll go through how scientists actually study the possible impacts of climate change, what kind of uncertainties we are dealing with, and the main impacts of climate change on Europeans forest ecosystems.

How Do Scientists Investigate Climate Change Impacts?

First of all, I want to clarify how scientists study the potential impact of climate change on forest ecosystems. This is important because by understanding how predictions are made, we can quantify the uncertainties underlying such predictions and why we should not blindly assume they are exactly what’s going to happen. Scientists use different types of models to predict how parameters, like tree species distribution or forest productivity, will change within a specific time frame (typically only until 2100, as uncertainties tend to become much larger as time proceeds). The Intergovernmental Panel on Climate Change produce large-scale reports on a regular basis, which prescribe different climate change scenarios ranging from the best to the worst cases in terms of greenhouse gas emissions and temperature increase. Scientists use these scenarios to model climate change impacts on forests in their study area, be it a single forest stand, a country, a continent, or even the whole world.

Below are a list of the changes that will likely occur in Europe, a continent with very diverse forests ranging from boreal to Mediterranean biomes. I chose this focus because I’m researching in Europe and thus my knowledge is based mostly on the research in this part of the world. However, due to the variety of biomes that can be found in Europe, the following can be extrapolated to a certain extent. Overall, the impacts of climate change will depend a lot on regional climatic and local site conditions but a common scientific ground about what will likely happen in forests does exist.

Linnansaari National Park, Finland (Image Credit: Héctor Abarca Velencoso, CC BY 2.0)

Forests are very dynamic. On the one hand, they provide habitat for many different animal species, regulate water and air quality, and protect soils. On the other hand, they are exposed to extreme weather events like windstorms and can suffer from forest pests, diseases, and pathogens. If you are in the Mediterranean basin, fire is another factor that occurs frequently. In a functioning ecosystem, these forest dynamics are well balanced but throw climate change into the game and soon enough this delicate balance will be disturbed. So based on climate change models, what are the main impacts on forests that can be expected over the next centuries?

• Increased forest growth and productivity: due to increased CO₂ in the atmosphere, forests are expected to grow faster. However, only if other parameters like water availability are not limiting this.
• Tree species movements: the relaxation of temperature constraints at the leading edge of a species range will allow slow migration to newly suitable habitats. On the opposite, the rear-edge habitat might become unsuitable due to changed conditions (i.e. lack of water). Scientific evidence suggests that the latter is happening faster than the former, potentially leading to the decrease of forests. Additionally, models only predict the future habitat suitability of a species while the actual response and migration capacity of species is not known.
• More frequent or extreme disturbances: An increasing level of fire danger, especially in the Mediterranean region but also in Central Europe, is predicted. Pest outbreaks will increase directly through the effects of increased temperatures on insect population growth and increased habitat availability and indirectly by affecting the vitality of the trees due to drought and water stress. Natural extreme events like windstorms, flooding, landslides, and droughts are predicted to increase. However, we have to keep in mind that all the before mentioned disturbances are stochastic events and thus not easy to include in climate change projections. Due to this, current research usually neglects their possible impact. Additionally, climate change predictions usually present mean values over a specific time horizon as results, but forests only partly respond to changes in climate means. Many changes in forests happen as a response to extremes. Thus, the lack of such extremes in current modeling schemes causes considerable uncertainties when assessing the likely response of forest ecosystems. In combination with other uncertainties like the actual adaptation and migration capability of tree species, make predictions only reliable to a certain extent.
• Implied effects on the environment: More severe and frequent wildfires will lead to the release of carbon into the atmosphere. Fires, other natural hazards, and disturbances like forest pest outbreaks will likely lead to the loss of biodiversity, changed water regulation functions, and increased soil erosion.

Our Role Going Forward

Forests are crucial for the fight against climate change. However, forests in Europe and many other parts of the world, have been managed by humans for many centuries, to the point that Europe has precious little natural forest left. Thus, a very powerful tool to reduce the impact of climate change, a human-induced phenomenon, is again in the hands of humans. Tree growth and forest adaptation take time, thus management decisions that are taken now will not show their effect immediately but only within the next couple of centuries. Another complication is the fact that forest stands which are great at storing carbon are often poor for biodiversity. For more on this issue, read yesterday’s paper review.

Due to this, forest managers need to implement strategies regarding climate change right now without knowing if their measurements are the right ones. The goal would be to create more resilient forests that will be adapted to changing future conditions. Climate change models are a powerful tool to support such decisions. Nevertheless, uncertainties are inherent to the system we are trying to forecast and thus unavoidable. As waiting for improved evidence and information cannot be the solution, scientists and forest managers are faced with a lot of challenges. You are probably thinking right now (at least I hope so) about what humans can do to prepare our forests for the changes to come. The good thing about the existence of models that include climate change predictions is that they allow potential solutions to be investigated. So fear not, my next article will at least answer some of your questions!

Julia Ramsauer is a landscape ecologist currently working on the integration of ecosystem services in the Mediterranean region. To keep up with her work, or listen to the latest episode of her podcast, Environmental Science Careers, you can follow her on Twitter here.