Reducing vulnerability to wind damage in forest management planning

December 11, 2024
A Caucasian woman with long, straight brown hair and brown eyes smiles in front of a neutral background.
Irene de Pellegrin Llorente. Photo courtesy of de Pellegrin Llorente.

Research Assistant Professor Irene de Pellegrin Llorente is investigating how to create a forest management plan that reduces a forest’s vulnerability to wind damage. The project is based in southern Sweden in a private forest dominated by Norway spruce (78% of volume), Scots pine (18%), and birch (4%). This research is funded by the Mistra Digital Forest and is in collaboration with the Department of Forest Resource Management at the Swedish University of Agricultural Sciences (SLU). It is expected to be published in the new year.

Here, de Pellegrin Llorente speaks with us about her work.

What research question are you asking?

Forest management planning models are strategic guidelines for how a forest is going to be managed for the following 50, 70, or 100 years. Because they tend to account for large areas, this type of modeling usually cannot carry a lot of detailed information, such as the spatial arrangement of the stands in a forest. Adding spatial information can make any management problem much harder to solve because management decisions for one stand must also include considerations of what is happening in neighboring stands.

Managing a forest to reduce vulnerability to wind damage is a spatial problem. That means that management decisions made for one stand can impact the wind-damage vulnerability of adjacent stands. But wind damage vulnerability can be reduced by carefully planning where and when different forest management activities, such as harvesting or thinnings, are scheduled.

With this research, the question we are assessing is: Can we create forest management plans that look at the production of timber and, at the same time, minimize vulnerability to wind damage?

Bare deciduous trees dusted with snow in a forest. The ground is also dusted with snow.
Photo by Gustav Bergman and published on Flickr (https://z.umn.edu/9yq5).

Why is this important?

Windstorms have been an important natural disturbance in Europe in the last decades causing, at times, extreme timber losses. Two of the most recent and severe storm events in Sweden were Gudrun in 2005 and Per in 2007. Both had big economic impacts. The volume felled by the Gudrun storm event was close to Sweden’s annual harvest volume today (75 million cubic meters). Even though no large changes in storm frequency and intensity are expected during the rest of this century due to the changing climate, the susceptibility of boreal forests to wind damage is expected to increase due to the shortening of the frozen soil period, which weakens the anchorage of trees to the ground.

Besides shortened frozen soil periods, the risk of wind damage also depends on many other factors defined at the tree, stand, and landscape level. For one, different tree species have different vulnerabilities to wind damage due to their canopies and root structures. In general, conifers tend to be more susceptible to damage from wind than broadleaves. In Sweden, Norway spruce is one of the most vulnerable conifers when it comes to wind damage. The height of the trees is a key factor as well. There is a higher probability of wind damage in forest stands with tall trees compared to stands with shorter trees. In addition, increased growth rates due to longer vegetation periods in boreal forests may lead to larger tree heights at younger ages and, consequently, an increased probability of wind damage at younger ages. Other variables affecting the risk for wind damage are stand density, site characteristics, forest fragmentation at the landscape level, local wind climate, and the removal of biomass through thinning and final felling.

How are you approaching the topic?

The first part of the project is theoretical: developing a wind damage index, which represents how vulnerable a stand is to wind damage. The index is developed by taking into account stand properties, such as tree species, the height of the trees, the relationship between the height and the diameter of the trees, the time since the last management activity was performed in the stand, and other density-related measurements.

After the index is parameterized to Swedish conditions, such as weather and soil, it gets integrated into a landscape-level forest management model. These types of long-term, large-scale models tell landowners how and when to schedule forest management decisions to achieve a certain goal. By tracking the wind damage index of each stand over time, we can then see whether the management activities potentially scheduled to happen will increase or decrease the overall vulnerability of the forest to wind damage. After integrating this information, the forest planning model selects the best management alternatives that optimize timber production over time, while also maintaining or reducing the vulnerability to wind damage.

In other words, this model aims to provide a tool for foresters, landowners, and decision-makers to help schedule different management activities in their forest lands that are spatially coordinated in order to reduce the vulnerability to wind damage while still meeting the overall forest management goals and objectives. 

~ This article is part of the Fall 2024 Forest Scene newsletter (Issue 32). Access additional articles in the table of contents that follows the image description.   

Image descriptions:

  • Image 1: A forest in winter with bare deciduous trees. Snow dusts the ground and frost covers the trees' branches. The sky appears almost white. 
  • Image 2: A light-skinned woman with long dark hair and brown eyes. smiles with her mouth closed in front of a gray background.
Cover of Forest Scene Issue 32, Fall 2024.

The Forest Scene newsletter is published biannually in the spring and fall, featuring stories, research briefs, and updates from the Department of Forest Resources. 

Click the following links to read articles from the Fall 2024 edition of Forest Scene (Issue 32):