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Forest edge quantification by line intersect sampling in aerial photographs
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Forest Resource Management, SLU, Umeå.
2006 (English)In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 230, 32-42 p.Article in journal (Refereed) Published
Abstract [en]

There is a need for accurate and efficient methods for quantification and characterisation of forest edges at the landscape level in order to understand and mitigate the effects of forest fragmentation on biodiversity.We present and evaluate a method for collecting detailed data on forest edges in aerial photographs by using line intersect sampling (LIS). A digital photogrammetric system was used to collect data from scanned colour infrared photographs in a managed boreal forest landscape.We focused on high-contrast edges between forest (height ≥10 m) and adjoining open habitat or young, regenerating forest (height ≤5 m). We evaluated the air photo interpretation with respect to accuracy in estimated edge length, edge detection, edge type classification and structural variables recorded in 20 m radius plots, using detailed field data as reference. The estimated length of forest edge in the air photo interpretation (52 ± 8.8 m ha-1; mean ± standard error) was close to that in the field survey (58 ± 9.3 m ha-1). The accuracy in edge type classification (type of open habitat) was high (88% correctly classified). Both tree height and canopy cover showed strong relationships with the field data in the forest, buttree height was underestimated by 2.3 m. Data collection was eight times faster and five times more cost-efficient in aerial photographs than in field sampling. The study shows that line intersect sampling in aerial photographs has large potential as a general tool for collecting detailed information on the quantity and characteristics of high-contrast edges in managed forest ecosystems.

Place, publisher, year, edition, pages
Amsterdam: Elsevier , 2006. Vol. 230, 32-42 p.
Keyword [en]
Canopy cover, Edge influence, Forest fragmentation, Line intersect sampling, Photogrammetry, Tree height
National Category
Ecology
Research subject
Ecological Botany
Identifiers
URN: urn:nbn:se:umu:diva-7415DOI: 10.1016/j.foreco.2006.04.012OAI: oai:DiVA.org:umu-7415DiVA: diva2:147086
Available from: 2008-01-09 Created: 2008-01-09 Last updated: 2017-12-14Bibliographically approved
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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