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Forest edge density in a gradient of boreal landscapes in Sweden
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Forest Resource Management, SLU, Umeå.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
(English)Manuscript (Other academic)
Abstract [en]

The boreal forests in Fennoscandia are strongly fragmented by intensive forestry and other land use resulting in high amount of edge habitat. Detailed data on edge quantity is critical to assess fragmentation effects on biodiversity. We estimated the density of sharp forest edges in 28 landscapes, each 4 km × 4 km, along a 830 km gradient in northern Sweden. Data was collected from colour infrared aerial photographs using line intersect sampling and 20-m radius plots. Forest edge density was 54 ± 4.6 m ha-1 land area (mean ± SE) but variation was high among landscapes (12-102 m ha-1). Natural edges constituted 38% but created edges dominated (36% maintained and 26% regenerating). Thirty percent of edges adjoined narrow (5-19 m) open landscape elements (corridor edges) and seventy percent adjoined more exposed patches (≥20 m, patch edges). We found 34 types of patch edges, with the highest density recorded for edges in mature forest. Edge density increased with proportion of landscape disturbed by forestry and agriculture, and decreased with latitude and altitude, but natural and created edges showed contrasting patterns. The high density of sharp edges and the variability among landscapes implies that edges may have strong and diverse effects on the structure, function and biodiversity of boreal forest ecosystems. This variability must be taken into account when formulating strategies for sustainable forest management.

Keyword [en]
line intersect sampling, aerial photographs, forest fragmentation, edge influence, edge length, edge types
National Category
Ecology
Research subject
Ecological Botany
Identifiers
URN: urn:nbn:se:umu:diva-21660OAI: oai:DiVA.org:umu-21660DiVA: diva2:211433
Available from: 2009-04-15 Created: 2009-04-15 Last updated: 2012-02-01
In thesis
1. Forest edges in boreal landscapes - factors affecting edge influence
Open this publication in new window or tab >>Forest edges in boreal landscapes - factors affecting edge influence
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The boreal forest in Fennoscandia has been subjected to major loss and fragmentation of natural forests due to intensive forestry. This has resulted in that forest edges are now abundant and important landscape features. Edges have documented effects on the structure, function and biodiversity in forests. Edge influence on biodiversity is complex and depends on interactions between many local and regional factors. This thesis focuses on sharp forest edges and their potential to influence biodiversity at the landscape-level. I have developed a method for quantification and characterization of sharp forest edges by interpretation of colour infrared (CIR) aerial photographs in combination with line intersect sampling (LIS) and sample plots. The method was used to estimate density of forest edge in 28 landscapes (each 1600 ha) in northern Sweden, differing in management intensity, landscape composition and geographical location. Forest edges were described in detail using edge, canopy and neighbourhood attributes. By combining these attributes it was possible to classify edges with respect to levels of exposure. A field experiment was conducted to examine the effect of edge contrast on growth of the old forest lichen Usnea longissima. The edge quantification method is accurate and efficient for estimating the length of sharp forest edges on an area basis (edge density, m ha-1) and for collecting detailed attributes of edges and their surroundings. In northern Sweden, the forest edge density is high (54 m ha-1) but varies extensively (12-102 m ha-1) between landscapes. Edge density is strongly correlated with the level of human disturbance and increases towards the southern part of the study area, at lower altitudes were management intensity is highest. Edge orientation, contrast and neighbourhood size shows an immense variation between edges and also varies between edge types. Regenerating edges are generally of higher contrast and face larger neighbourhoods than natural edges. Maintained edges had high contrast but small neighbourhoods. A larger proportion of edges in mature forests are highly exposed to microclimatic edge influence than edges in general. The field experiment revealed that growth of U. longissima was highest near edges where the vegetation on the adjacent area was sheltering, but not shading, the lichen. In the present thesis, I have provided a valuable tool for estimating density of forest edges with potential to yield information on important factors determining edge influence at landscape-level. The large variability in edge density, edge and neighbourhood attributes imply large differences in microclimate anf thus in the potential for ede influence. Management and conservation strategies must incorporate these factors to realistically address edge influence on biota at the landscape-level.

Publisher
41 p.
Keyword
aerial photographs, edge contrast, edge density, edge length, fetch size, forest fragmentation, lichen growth, line intersect sampling, pendulous lichen, photo interpretation, skogskant, flygbild, kantlängd, lav
National Category
Ecology
Research subject
Ecological Botany
Identifiers
urn:nbn:se:umu:diva-21664 (URN)978-91-7264-756-5 (ISBN)
Public defence
2009-05-08, Lilla Hörsalen, KB3A9, KBC, Linneaus v. 6, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2009-04-17 Created: 2009-04-15 Last updated: 2009-04-17Bibliographically approved

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CiteExportLink to record
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Citation style
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  • de-DE
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  • Other locale
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Output format
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  • text
  • asciidoc
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