Plant biodiversity in European forests is declining

(15-05-2020) In European forests, environmental changes cause forest plant biodiversity to decline, shows international research with Ghent University.

The research team published numbers on the effects of environmental changes such as climate change, enhanced nitrogen inputs in the forest ecosystem, and a change in forest management on more than 1,000 plant species in European forests. The project is especially valuable in the fight against biodiversity loss as stated in the EU’s Green Deal measures.

Based on their findings, the researchers conclude the following:

  1. Plant diversity in temperate forests is declining (published in Nature Ecology & Evolution).
  2. Tree canopies protect forest life from global warming (published in Science).

Plant diversity is declining  

Less common and specialized plant species are being replaced by more widespread species. The scientists could link this evolution to an increase in nitrogen deposition in forests.

Professor Lander Baeten (faculty of Bioscience Engineering at Ghent University) explains: “Forests receive more nitrogen than before. This changes the competitive interactions between plant species: more widespread species benefit more from the higher nitrogen inputs and grow faster, at the expense of the more specialized species that tend to have an increased risk of extinction. In the end, forests will become more homogenous, because the same suite of species is found everywhere.”

Treetops protect forest life against global warming

The scientists also proved the importance of a dense tree canopy. The cooling effect of the canopy protects forest plants and animals against extreme temperatures, which influences their ability to resist global warming. 

Professor Pieter De Frenne (faculty of Bioscience Engineering at Ghent University): “If the canopy is more dense, it buffers the climate warming for the organisms living underneath. If the canopy becomes thinner, the temperature below quickly rises.”
“All organisms have an optimal temperature. When the climate gets warmer, the warm-affinity species will benefit. They can exclude the species that function best in cooler temperatures. Because of global warming, many species are now already living in a sub-optimal temperature range”, says De Frenne.  

Important for future forest management

If a forest canopy becomes thinner – either due to climate-induced disturbances such as pathogen attacks, wind throw and drought or because of human intervention – understorey plants will experience warmer air temperatures, to which many are maladapted. Considering the expected increase in heat waves in Europe, this could change the biodiversity in forests considerably. In addition, more open tree canopies can strengthen the negative impact of enhanced nitrogen inputs, because the fast growing species get more light, which causes them to increase even more in abundance.

“Forest managers should therefore consider the effects of forest management on the light and microclimate conditions in the forest. Their work can have a considerable impact on forest biodiversity”, says Professor Lander Baeten. 

Database for plant community change in forests

The scientists at Ghent University are also the driving force behind the forestREplot-database, used globally by researchers to map the changes in the composition of herb layers and the functioning of forests.

The data are also important to judge the effects of global environmental changes such as nitrogen deposition and climate change.

This project has received funding from the European Research Council (ERC) under the European Union’s projects FORMICA led by Prof. Pieter De Frenne and PASTFORWARD led by Prof. Kris Verheyen.

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