Remote sensing - Monitoring ecosystem disturbances

Defoliating insects

Insect attacks can be dynamic events by defoliating insects where trees usually survive the attack and sometimes refoliate later in the growing season. An example is the sub-arctic birch forest in northern Sweden that are attacked by defoliating birch moth larvae with cycles of 9-10 years.

We have developed a method to monitor these defoliation events in near real-time with MODIS data (250×250m spatial and 8-days temporal resolution) and we have studied how these defoliation events influence carbon uptake with a Light Use Efficiency (LUE) model. 

European spruce bark beetle

Another example of insects is the European spruce bark beetle that attack and kill spruce trees. The bark beetles are naturally present in the forests and at low populations they only attack and kill weakened trees.  Windstorms, when large numbers of storm-felled trees provide the bark beetles with breeding material, and droughts, that decrease the trees’ defense capacity, might trigger major outbreaks. Such disturbances may have large numbers of trees being killed. 

To prevent the beetle population build-up it is important to detect infested spruce trees early and remove them from the forest. We are using Sentinel-2 to study how early we can detect attacked trees and how many trees need to be attacked to enable detection.

Drought events

We study how ecosystems are influenced on a larger scale by drought events. Many European countries have suffered from severe summer droughts and have experienced multi-year droughts in the first two decades of the 21st century. In 2018, Northern Europe experienced a significant drought, resulting in severe forest fires and a decline in crop yields in Sweden. The impact on forest productivity continued into 2019. Over the entire Europe, vegetation growth responds to drought differently depending on growing stage and aridity, with higher sensitivity to drought in autumn or arid regions.