Bird biodiversity in relation to forest composition in Sweden

Abstract

The large development of timber activities in Sweden has induced important changes in forest composition. Today they are less old, deciduous trees and snags in Swedish forests. Such changes threaten the survival of certain bird species in Sweden. Today, bird biodiversity restoration plans try to re-establish, in harvested forests, the structural straits that will foster high bird diversity.

The aims of this study were: 1) to identify in the literature which forest composition traits are essential for forest birds in Sweden; 2) to find the environmental variables that explain the occurrence and abundance of forest bird species in Sweden, using regression analyses conducted on data from a national monitoring program. Those analyses were conducted for a group of species, considered as being indicator of forests with high quality habitats for birds.

Past studies have identified several main drivers of bird diversity, notably the presence of old standing trees, of decaying timber and the amount of deciduous trees. Lack of information on such variables limited the power of our analysis. However, regression models revealed the importance of forest edges, which can compensate the lack of deciduous trees in harvested forests. Thus in a biodiversity perspective the scope of concern should be broadened to the areas close to forests. The results of the analyses have also shown the importance of mixed forest for bird biodiversity, since such type of forest increases the nesting and foraging opportunities. The lack of clear links between the distribution of forest indicator species and forest composition traits in the data analysed also questions the practical relevance of indicator species as they are currently defined.

Popular Abstract

The population of certain bird species has decreased for the last 30 years in Sweden. Some experts directly link those losses with the human-induced transformations, which has occurred in Swedish forests.
Actually, forestry is largely developed in Sweden. Commercial forestry represents an important source of income for the Swedish economy. This sector appears to have a negative impact on bird biodiversity. As a consequence of timber activities, today they are less old, deciduous trees and snags in forests. Bird biodiversity restoration plans try to regulate timber activities in order to re-establish in harvested forests the structural traits that are essential for the survival of birds.
The first aim of the study was to clearly identify such traits, in analysing works and studies done by experts in birds' ecology. Then the repartition of certain birds species, considered as forest specialists, were statically analysed. These analyses were carried out at a national scale, using environmental data and forest maps. The goal was to understand why certain forests welcome more birds than others do, and which composition traits could explain a higher or lower abundance of birds.

It appears that it is the elements, which are pretty scarce now in Swedish forests (because of harvesting methods) that are the most important for birds (old standing trees, decaying timber and the amount of deciduous trees). The statistical analyses have revealed the importance of the areas in the surrounding of forests. Actually, in those areas, birds can find what lack inside forest: deciduous trees to nest and forage on, a foraging surface where they can find ants for example, the presence of fruit-bearing shrub and thickets because of the greater sun exposure. The results of the analyses have also shown the importance of mixed forest for bird biodiversity, since such type of forest increases the nesting and foraging opportunities. The role of old trees has not been highlighted as excepted. It may be linked to the defaults of our data and methods, but we could also conclude that harvested forests almost never get old enough to really benefit the species that require old stands.

As a conclusion of this work, 3 action plans could be suggested to managers who draw up bird biodiversity restoration plans. First it is essential to ensure the presence of old stands trees in forests. Second, it seems important to replace monoculture of coniferous trees by polyculture, and thus increase the proportion of deciduous trees. Third, biodiversity restoration plans should consider the protection and the management of forest edges.

• author: Finck, Annabelle
• supervisor: Paul Caplat; Veiko Lehsten
• organization: Dept of Physical Geography and Ecosystem Science
• course: NGEM01 20141
• year: 2015
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: timber production, bird biodiversity, indicator species, forest composition, bird occurrence, Physical Geography and Ecosystems Science
• publication/series: Student thesis series INES
• report number: 328
• language: English
• id: 4940512
• date added to LUP: 2015-01-23 14:50:47
• date last changed: 2015-01-23 14:50:47