Epsilon Archive for Student Projects

Abstract

Forest management in Fennoscandia has nearly eliminated natural disturbances, such as fire, from forest ecosystems. This affects the composition of tree species, the availability of deadwood, and saproxylic beetle communities. Restoration methods such as prescribed burning and tree girdling aim to replenish the deadwood supply in boreal forests. Prescribed burning creates habitats that benefit fire-dependent beetles and influences successional patterns that benefit Scots pine (Pinus sylvestris). Tree girdling adds to already existing deadwood pools and provides a high variety in decay classes that benefit many generalist beetles. Both methods were applied at three treatment areas per method across three years (2022, 2023 and 2024) in Ekopark Ejheden, an area with a long history of fire.
Deadwood volumes of six individual treatment areas, three for each treatment method and year, were calculated separately for snags and logs. Deadwood volumes, abundance, richness, diversity and composition values were used to compare between treatment methods. No significant differences in deadwood volumes were found. Deadwood abundance, richness and diversity were significantly higher in burnt plots at three years post-treatment than in girdled plots. Deadwood composition differed significantly between treatment methods and years. The indicator deadwood category composition showed that stands treated with prescribed burning produced logs and snags in intermediate decay classes. Stands treated with tree girdling produced logs in a wider range of decay classes, including very early to late decay stages.
Ecletor traps were used to sample saproxylic beetles and abundance, species richness and diversity values were used to compare treatment methods. Beetle abundance and species richness were shown to be significantly higher in areas treated with prescribed burning than in tree girdled areas at one and two years post-treatment. Beetle diversity was significantly higher for prescribed burning at two years post-treatment. At three years post-treatment, no significant differences were detected. Beetle composition differed significantly between treatment method and time since treatment. Indicator species analysis showed 19 beetle species that were almost exclusively associated with prescribed burning and three species that were exclusively associated with tree girdling.
My results show that both prescribed burning and tree girdling are effective tools for increasing the deadwood supply in boreal forests. Prescribed burning and tree girdling produce different deadwood categories, which can be interpreted in terms of how the methods act across the plot. Prescribed burning is shown to be clearly favoured by fire-associated beetle species, supporting the argument that fire as a disturbance is irreplaceable by any other method. Regardless of this, tree girdling is a valuable method for promoting the accumulation of deadwood in boreal forest ecosystems. This method should be regarded as an additional benefit rather than a replacement of prescribed burning.