New Monitoring Tool Reveals Declining Forest Health Across Germany

New Monitoring Tool Reveals Declining Forest Health Across Germany
by Robert Schreiber
Berlin, Germany (SPX) Aug 13, 2024

Germany's forests, covering approximately one-third of the country's land area, have been thoroughly mapped in terms of distribution and dominant tree species. However, there has been a lack of comprehensive data on the overall condition of these forests across large regions and how this is changing over time. "What we are missing to date are specific information on large-scale and area-wide forest condition which still include regional aspects and its change dynamics," says UFZ remote sensing specialist Dr. Daniel Doktor.

To address this, the Helmholtz Centre for Environmental Research - UFZ has developed a new forest condition monitor. "We have developed an index representing the dynamic condition changes in Germany's forest areas. This index is displayed as seasonal and annual maps within our monitor," Dr. Doktor explains. Unlike the German Federal Ministry of Food and Agriculture's (BMEL) forest condition report, which provides statistical samples from roughly 400 forest plots with a 16-kilometer resolution, the UFZ monitor offers more detailed spatial and temporal data.

The UFZ researchers utilized Sentinel-2 satellite data from the European Space Agency (ESA) to assess forest conditions. "Sunlight is reflected differently by each tree species over the course of the year. This can be captured very well by the satellites, which store the information as numerical values. They depict vegetation characteristics, e.g., pigment and water content or canopy structure," says Dr. Maximillian Lange, the study's lead author.

By comparing the reflectance data from 2016 to 2022 against reference values for healthy populations of the four dominant tree species-oak, European beech, Norway spruce, and Scots pine-the researchers developed a "forest condition anomaly index." This index measures deviations from expected reflectance values, indicating how much the current forest condition differs from what is typical. The monitor provides this information for all forested areas in Germany at a 20-meter resolution, though challenges remain in calibrating the index and minimizing uncertainties.

The UFZ forest condition monitor not only maps forest condition but also tracks the distribution and phenology of the four dominant tree species, including details like bud burst and leaf coloration. The platform also includes multiple vegetation index maps highlighting specific vegetation properties and modelled tree species distribution maps based on three climate scenarios outlined by the Intergovernmental Panel on Climate Change (RCP 2.6, RCP 4.5, and RCP 8.5).

The primary feature of the UFZ monitor is the forest condition anomaly maps, which quantify conditions on a scale from -1 to 1. Positive values, shown in green, indicate improving conditions such as increased chlorophyll and water content, while negative values, ranging from yellow to dark violet, signify damage or stress. For instance, values below -0.15 are generally associated with severe damage from factors like drought, windthrow, fire, or insect infestations.

The maps reveal a dramatic increase in forest damage in central Germany, including the Harz region, Thuringian Forest, Sauerland, and Saxon Switzerland, particularly after 2018. By 2022, the monitor showed that 52 percent of Germany's forests-and 76 percent of conifers in the Harz region-suffered severe damage. In contrast, only 9 percent of forests and 8 percent of conifers were severely damaged in 2017. UFZ researcher Anne Reichmuth explains, "Heat, drought and insects as well as their interaction negatively affect the forest and result in subsequent damage such as windfall and elevated risk of fire."

Post-1945 spruce plantations in central German uplands have been particularly hard hit, but significant losses have also been recorded among pines, beech, and oak trees. Insect outbreaks are a major factor in the decline of conifers, while deciduous trees are increasingly affected by complex diseases that weaken their immune systems.

The UFZ monitor also shows how extreme climate events have varying impacts across regions. For example, the forest condition in the Black Forest and Erzgebirge (Ore Mountains) remained relatively stable from 2016 to 2022. The silver fir, common in the Black Forest, appears better adapted to climate change compared to the Norway spruce. Central and northeast Germany, however, experienced more severe drought impacts, though higher elevations in the Erzgebirge were less affected.

"The UFZ forest condition monitor especially seeks knowledge transfer to the authorities, such as the federal state forests and the national park authorities," says Dr. Doktor. The maps provide a clear visual representation of how climate extremes are driving changes in forest ecosystems.

Research Report:A continuous tree species-specific reflectance anomaly index reveals declining forest condition between 2016 and 2022 in Germany