Exploring patterns in risk factors for bark beetle attack during outbreaks triggered by drought stress with harvester data on attacked trees: A case study in Southeastern Sweden

Abstract

ABSTRACT
Raising temperatures and climate variability have intensified extreme weather events worldwide. These extremes can enhance and trigger possible pest outbreaks. Bark beetle attacks have become a major concern in regions with extensive spruce forest areas. Southeastern Sweden has faced repeated outbreaks resulting in widespread tree loss. By observing historic climate data for the main counties of Southeastern Sweden we can notice that the temperature is progressively raising. Rainfall do not manifest a clear pattern but it follows a descending trend. Water shortage can lead to drought events for the specific area.
The main triggering factors for a bark beetle outbreak are a storm damage or a drought stress. In this study we used data and try to model an outbreak that was triggered by drought stress in 2018. This study focused on proactive risk management. Data from 2018 and 2019,2020 were combined to create two main datasets. One from 2018 which was considered a drought year and one that emerge from the years 2019 and 2020 which were considered more “normal” year from a meteorological perspective.
The model used overlay analysis in ArcGIS environment between attacked trees and predisposing factors like soil moisture, topography and landcover data. Th goal was to investigate intervals of risk factors that could raise the potential risk. These factors could in some cases attribute higher danger in specific regions. Furthermore, a risk map was created by utilizing a weighted overlay model. All the abovementioned parameters were considered of equal weight.
Some final things to consider about improving the specific model. Firstly, the unique type of the dataset that contained attacked trees. This dataset was collected by harvester machines which were equipped with GNSS devices. The attacked tree was attributed the coordinates of the body of harvester or the crane. This could result in a different landcover classification than the actual and it is an uncertainty in the findings of this study. A soil wetness index was used to examine the effect of soil wetness. This was a static dataset. It was the same dataset for the 2018 and 2020. Possible correlations between risk factors were not examined. Topography and soil moisture are considered to correlate in some cases but it was hard to quantify in this study. No statistical test was used to support the findings. Finally, the spatial propagation of the outbreak was not imported as a parameter in the specific model. It is possible that the outbreak started in 2018, cumulatively raised the numbers of bark beetle in the following years.

Popular Abstract

Pop Abstract
In recent years, bark beetle outbreaks have intensified causing damage to forests in many parts of the world. Forest ecosystems of Northern Hemisphere are considered more vulnerable because of their tree composition. Vast areas are covered by spruce forests which is a favorable type for the specific pest. Forest ecosystems provide many services and secure the wellbeing of wildlife and citizens. Protecting their structure and functionality is of the utmost importance. Other factors may contribute to the damages caused to forest ecosystems like outdated forest management policies. Furthermore, land use systems and guidelines that are not adjusted to the specific characteristics of a region. Another factor to consider is the percent of privately-owned forests, in some cases, which makes it difficult to communicate the hazards and follow some harmonized standards.
Physical characteristics of a region and topography are parameters that can enhance the potential risk if other factors coexist as well. An event like a storm damage or a drought stress is usually the triggering factor for the beginning of the outbreak. The predisposing factors contribute to the rapid spatial propagation of the outbreak among with favorable climate conditions like temperature and drought. Southeastern Sweden is a region considered to fit the abovementioned description. Extreme events initialize a bark beetle outbreak which results in greater damages due to higher number of bark beetle. Climate crisis favors the breading process of bark beetle which results in higher number of bark beetle during their lifecycle.
In this study, we focused on the environmental perspective of the bark beetle outbreaks. GIS techniques were used to analyze the risk factors associated with bark beetle outbreaks. By mapping trees that were attacked by bark beetles, we were able to identify patterns and trends in the risk factors. Data about attacked trees were provided by Skogsstyrelsen (Swedish Forest Agency). Landcover data were given by Naturvårdsverket (National Landcover Data). Soil moisture and topographic data were used which were provided by Lantmäteriet and Swedish Agricultural University (SLU). The goal was to investigate intervals of risk factors that elevate the potential bark beetle. Furthermore, a risk map was created indicating high-risk regions which could help to allocate preventive measures and resources.
As mentioned above forest management and bark beetle outbreaks are multidimensional concepts that require cooperation of many professionals and specialists. Sustainable management and policies are required to mitigate and tackle the outbreaks that are favored by climate conditions like temperature and water shortage. A model that incorporates various types of criteria (social, environmental, financial), data-driven decisions and location-specific management is the way to proceed in the future.

• author: Kouskoulis, Nikolaos
• supervisor: Per-Ola Olsson
• organization: Dept of Physical Geography and Ecosystem Science
• course: GISM01 20232
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Geography, GIS, Geographic Information Science, Forest ecosystems, Bark beetle outbreak, Southeastern Sweden, Predisposing factors, Triggering factors, Drought stress
• publication/series: Master Thesis in Geographical Information Science
• report number: 164
• language: English
• id: 9137156
• date added to LUP: 2023-09-13 15:52:37
• date last changed: 2023-09-13 15:52:37