Due to the bark beetle calamity, which has hit the Czech Republic hard during the last 10 years and decimated fragile spruce monocultures, many patches of forest have been cut down. This situation makes forest floors vulnerable, which is particularly problematic in the context of global warming since forests are more needed than ever as stable carbon storage. As described in our previous article, forest soil contains about two thirds of the total carbon stored in the forest. Scientists from Mendel University, the Research Institute of Forest Management (VULHM) and the Czech University of Life Sciences in Prague (CZU) are therefore working together to monitor the situation closely and better understand the processes occurring in soil decomposition. Photos credit: Coline Béguet / Brno Daily.
Czech Republic, July 19 (BD) – Forests are widely understood as “the lungs of our planet”. But what is less understood by the public is the importance of forest soils, where the majority of forests’ carbon is stored. Vegetation itself is more than half composed of carbon, which is taken from the atmosphere by photosynthesis: plants build themselves with the carbon they catch in the air. Then, when dead leaves, branches or entire trees die and fall to the ground, they continue to hold the carbon inside their cells, until they slowly decompose, eaten by insects and the forest microbiome. This creates a first layer of soil, called the forest floor, full of dead vegetal matter and therefore carbon.
“In the whole forest ecosystem, you generally have one third of carbon stored above ground, in vegetation, and two thirds in the soil, especially in organic soil matter,” explains Radek Novotny, scientific researcher at VULHM and coordinator of this current research project on forest soil carbon. In the meantime other plants grow, capturing carbon again, which creates a life cycle in which carbon is stored in a stable way.
However, when a forest is damaged by factors related to climate change, such as drought, forest fires, or over-proliferation of wood-eating insects such as bark beetles, it disrupts not only the process of carbon capture by vegetation, but also the storage of carbon in the forest soil. “If the forest stand is healthy, then the ground is shaded by tree crowns; the sun’s rays cannot directly reach the forest floor and soil organic matter can decompose more slowly,” says Novotny. But when the vegetation is not present to create a microclimate and protect the soil from the direct radiation of the sun, the decomposition process accelerates. Sunlight and heat allow insects and microbiomes to multiply more quickly, just as global warming caused the population of bark beetles to explode.
Moreover, these parameters are very complex, and interact with other factors, which is why the current study has begun, dedicated to monitoring the phenomenon. “We have huge clearcuts, and it is clear from the outset that these clearcuts influence the water regime of the landscape, which means air humidity and the amount and quality of stream water,” continues Novotny. “But the next question is how these clearcuts influence carbon sequestration and the balance between carbon sinks and carbon pools. So that’s why we prepared and established this project.”
“The project is only for three years, which is a very short study, and we are in the first year of this project. This year and next year we are sampling soils, analyzing and collecting the data,” he explains. “Then, during the third year we will have to prepare some conclusions for state administration and try to provide answers on how much organic soil matter is decomposed in clearcuts, how quickly the ground decomposes, and finally how dangerous the situation is.”
For this study, the team are using the plots and methodology of the international ICP forest monitoring project, which was initially created to monitor the effect of air pollution on forests, but serves now as a framework for studying many other aspects of forest ecosystems. In this project, different kinds of samples are taken regularly all over the country and various observations are made. “We can then test and find relationships between parameters and tree or ecosystem conditions. For example, how does temperature influence tree increments? Or, how does the amount of water in the soil influence tree vitality?” says Novotny.
Teams from around Europe then upload their data to European-level databases, allowing all participating researchers to work with a huge set of data, assessing spatial, temporal, or any other relationships between forest stand parameters, such as growth, nutrition, concentration of elements in soil, and so on. For this reason, it is crucial that all countries should work according to the same methodology, so the data from all European countries can be used to explain how forest ecosystems work and how they are coping with current challenges such as climate change.
“So this year, in our project, we established plots with organic matter decomposition experiments across the whole country. We selected two different management strategies of the clearcuts that we are comparing. When trees are harvested, the stems are sold and branches cut. You can then clear all the logging residues from the clearcuts, which means branches and bark, or you can chop them with special equipment and cover the cut area with these small chips of wood. So we have experimental plots on these plots with chopping, without chopping, and control plots in healthy forest.” In this way, Novotny and his team hope that they will be able to compare how quickly organic soil matter decomposes in clearcuts managed via these two different approaches, and in healthy, standing forests.
The second part of the project involves a comparison of the chemical and biological composition of forest soils, up to 30 cm of depth. The team will analyse all soil layers separately, from the surface of the forest floor, then the soil from 0 to 10 cm, from 10 to 20 cm and from 20 to 30 cm. The analysis will measure the concentration of elements as well as biological activity. The third part of the project is soil pits, where the soil is analysed to a depth of one metre, and fourth part is the evaluation of water chemistry in stream water in small forest catchments. “We have two or three small forest catchments which we have been monitoring for more than 10 years. Within these catchments are new clearcuts and we would like to try to compare the chemistry of the stream water after clearcutting, to see if this causes some changes in the water chemistry.”
For the second part of the project, the soil pits, the researchers dig large holes of one cubic metre. After rescuing all the frogs that have fallen into the hole during the night, Věra Fadrhonsová, forest engineer at VULHM, takes detailed notes of the visual aspect of each layer of the soil. The colour and the texture can provide some initial indications about the composition and type of soil.
She then takes samples at different depths which will be analysed at the laboratory. They are taken starting from the bottom, in order to avoid contamination if pieces of soil fall. They are taken at ever closer intervals as they get nearer to the surface level, because the layers of soil are finer and their compositions more varied. Deeper layers are mainly made of mineral matter, and upper layers of organic matter. When examining the carbon content of the soil, these upper layers are also the most important, because this is where the majority of undecomposed dead plant matter, and therefore carbon, is found.
Next, in order to avoid bias and to make the collected data more reliable, additional samples are collected at regular intervals around the main hole. This allows for conclusions to be reached corresponding more to the general state of the soil in the given research plot, without being influenced by the small variations between one specific spot and another, or from one metre to another. For these, a manual coring device is used and, again, samples are taken at defined depth intervals and are then mixed with the first ones.
Finally, to obtain more precise information on this precious first layer of the soil, one more type of sample is taken. A metal square serves as a measure; it is placed on the ground several times in different places around the large main pit, in order to cover the different small variables present in the area studied: under a tree, in the grass, under brambles, on bare ground, and so on. After removing everything that is alive (i.e. the leaves, blade of grass and insects), the totality of each of the first two layers of soil is harvested separately and packed in a plastic bag. This will make it possible in particular to assess the amount of carbon they contain.
Each sample is finally divided in three parts: “At Mendel University they are analysing microbiota activity in soil organic matter and in the first 10 cm of mineral soil,” says Novotny. “In our institute we are analysing, according to ICP forest methodology, the concentration of carbon, nitrogen and sulphur. We use a combustion method and a so-called weak solution – weak acid which is able to dissolve parts of elements which are available in the soil for tree nutrition, known as “available elements”.” The Czech University of Life Sciences in Prague, meanwhile, has special instruments for analysing the total amount and concentration of elements in the samples, so together these processes can calculate the “available” and “total” amounts of each element present, to determine how much is soluble and available for tree nutrition, and what is the whole concentration on the site and the ecosystem as a while.
“And we compare the same soil pits after some time,” Novotny continues. “We try to see if some changes in soil chemistry are visible one or two years after clearcutting, and between plots with forest stands and without. Because changes in soil do not happen so quickly; in soil the processes are slower than in air or trees, for example. So we need to observe the situation one, two or three years after the clearcuts. We expect that most changes are happening in the surface, meaning the first layer, the forest floor, and in the first 10 or 20 cm of soil.”
