Articles containing the keyword 'lightning'

The writer reports in this discussion article of four stands in Finland that have died due to a bolt of lightning. A death of a group of trees because of lightning has been relatively uncommon for the forest professionals. The trees may not have no lightning marks. The four sites are presented in detail. Characteristic for this type of death of trees is, for instance, that trees have died within a circular area (of usually 30 m of diameter), only conifers have died, trees die from the top down, sometimes marks can be found in trees in the centre of the area, and under the bark may be brown patches or stripes.

• Nuorteva, E-mail: mn@mm.unknown

Earlier studies have shown strokes of lightning as the reason for 42% of forest fires in Finland. The frequency in northern Finland has been three times higher than in more southern parts of the country or 1.5 times higher than in Sweden. Taking the climatic factors into account these figures don’t seem to be accurate.

The study is based on the statistics about thunders in northern Finland and the information on the forest fires. We know that though there has been a lightning it is not always that the lighting strikes on land and lights a fire.

From the statistics it can be seen that the most forest fires that are thought to be kindled by lightning, have occurred in the same time when there has been thunder and lighting. Thunders and strokes of lightning striking to the land are the most common reason for forest fires during the warmest summer in northern Finland. The knowledge that a proceeding thunder storm may kindle several forest fires in a row must be acknowledged when planning the fire fighting resources. 

The volume 34 of Acta Forestalia Fennica is a jubileum publication of professor Aimo Kaarlo Cajander.

• Keränen, E-mail: jk@mm.unknown

Fires are major disturbances in boreal forests, and forest fire risk is projected to increase in Finland. Despite this, comprehensive large-scale analyses evaluating multiple potential drivers of fire ignition and size remain scarce. The aim of this study was to assess how selected environmental and human-related factors influence the relative ignition probability and fire size in Finnish boreal forests. We utilized data on forest fire occurrence and size, the Finnish Forest Fire Index (FFI), and ignition cause, compiled by rescue authorities across mainland Finland during 2014–2023. We supplemented it with spatial data describing environmental factors (site trafficability, slope, canopy cover, and dominant tree species) and human-related factors (human population density and distance to nearest road). The dataset contained 10 284 forest fire observations and an equal number of pseudo-absence observations. We fitted one generalized additive model (GAM) each to explain relative ignition probability and fire size. The relative ignition probability model explained 51.6% of the deviance and achieved a classification accuracy of 83.7%, while the fire size model explained 21.5% of the deviance. Human-related variables were among the most influential in both models, with human presence increasing relative ignition probability but reducing fire size. Seasonality and weather were also significant, suggesting a major influence of weather and vegetation dynamics on fuel moisture, whereas dominant tree species affected only fire size and slope only relative ignition probability. The contrasting effects of humans on forest fires suggest potential for reducing future fire risk through targeted fire management strategies.

• Knaappila, University of Eastern Finland, School of Forest Sciences, FI-80101 Joensuu, Finland https://orcid.org/0009-0007-7130-1141 E-mail: aleksi.knaappila@uef.fi
• Lindberg, Häme University of Applied Sciences, School of Biotechnology and Natural Resources, FI-13100 Hämeenlinna, Finland https://orcid.org/0000-0001-9045-2673 E-mail: henrik.lindberg@hamk.fi
• Tanskanen, Karelia University of Applied Sciences, FI-80200 Joensuu, Finland https://orcid.org/0009-0008-1619-7000 E-mail: heidi.tanskanen@karelia.fi
• Aakala, University of Eastern Finland, School of Forest Sciences, FI-80101 Joensuu, Finland https://orcid.org/0000-0003-0160-6410 E-mail: tuomas.aakala@uef.fi