Climate change, pollution, invasive species, and forest management techniques in European forests present new growth conditions with no historical references. A change in water, nutrients, carbon dioxide, or light caused by climate change could affect how trees utilise these resources. The EU-funded DENDRONUTRIENT initiative set out to better understand how pollution and climate change will affect the growth patterns of European forests. “The main problem we are trying to solve is that we want to correctly predict the impact of global change on forest growth,” says DENDRONUTRIENT team leader Dr Federico Castillo. “We have to understand the long-term response of forest ecosystems to novel conditions such as climate change.” Pyrenees forests sampled The team studied the forests of the Pyrenees Mountains in south-west Europe to get a representative sample of European forests. They collected decomposing organic matter (leaf litter) on the forest floor along with samples of mineral soil from two distinct forests in the Pyrenees Mountains. ”Analyses of the chemical content of the litter provided data that was added to an 18-year record of the forest’s soil nutrient history. DENDRONUTRIENT members took stock of how many trees were dead, and how many were alive, while measuring their diameter and height to estimate the amount of biomass. They combined the biomass and chemical analysis data to estimate nutrients used and produced over 18 years in the forest. The team bored through trees to collect core samples, which they analysed for nutrient content and annual growth rates. They studied how nutrients had been distributed through the many years the individual trees lived since the 1980s. They used this information to calculate how the growth of the trees was affected by known environmental conditions such as the climate and CO2. Simulating forest growth Researchers developed improved software to estimate how trees grow, based on mathematical relationships between different ecological variables. They simulated each of the variables to gauge their individual influence on forest growth. DENDRONUTRIENT found that Scots pine forest growth in the Pyrenees will be reduced by 8.4 % to 12.7 % in the next 90 years. They found that nitrogen availability could either slightly increase tree growth (by 1.8 %) or reduce it by up to 11.5 %. They also found that CO2 increase will have a very small positive effect on tree growth, debunking the CO2 fertilisation effect. Obstacles overcome The project was not without its share of challenges: collecting soil, litter and wood samples in an appropriate fashion. Due to the sensitivity of the instruments, the researchers were forced to collect wood samples perpendicular to both the tree height and the mountain slope. This led to an extractor breaking on the slippery, steep slope and setting back the sampling operation. “This simple piece of equipment is made by order and therefore it would have taken several months before it could be replaced, and in that time the trees would have not stopped growing,” said Castillo. However, with patience and a bit of good fortune, the team reached all the research objectives. The future –at grass roots level The team hope to further expand on the tools they developed to understand how trees in this region grow, supplemented by a field data set spanning 18 years. They plan to better understand the below-ground component of forests, particularly roots, to produce more accurate estimations of future tree growth. Besides the scientific objectives, the DENDRONUTRIENT team has become better known at local and international level. The team now has links with the local branch of the Spanish National Radio broadcaster, who consults the team for its collaboration in popular science talk shows. “All these activities have promoted understanding of the importance of forest ecology in the province of Navarra,” Castillo says.
DENDRONUTRIENT, forest, climate change, tree growth, nutrients, Pyrenees Mountains