Climate and land-use change as driving forces in lowland semi-natural vegetation dynamics

Abstract

In many parts of Europe, extensive changes in vegetation have taken place during recent decades. In Norway, forest expansion is a major trend, with an increase in volume of 20.3% during the period 1994-2008. The annual increase has more than doubled since 1967. This study was carried out to gain more insight into the complexity of vegetation dynamics and alterations in a lowland area on the coast of W Norway, and to identify the driving forces behind these changes. Field surveys were carried out with aerial photo interpretation and vegetation mapping. Spatial analysis was carried out using GIS. Historical sources were identified, interpreted, and used to generate information on land-use during recent centuries. Supplementary methods consisted of soil profile analysis and dendrochronology. Climate data were used to analyse climatic trends in the past 90 years since 1923. Forest expansion was a major trend during 1956-1994. In 1956, 49.5% of the area was covered by forest, and by 1994 the coverage had increased with 53.4%. Forestation continued during 1994-2003 and 2003-2007, but at rates far lower than in the previous period (4.0 and 3.8% increases, compared to 53.4%). Forest expansion was most extensive during 1956-1994, a period with no clear trend in mean July temperatures. A distinct increase in mean July temperatures occurred during the period 1994-2003 and again in 2003-2007, when the rate of forestation was far lower than in previous decades. This is an indication that a factor other than climate change is the most important driving force for vegetation change, forest expansion in particular. Forestation did not start simultaneously throughout all parts of the study area, but at different times on different landholdings. Forestation initially started on plots where livestock grazing first came to an end (in the 1930s), and lastly on plots where grazing came to an end three decades later, in the 1960s. The different starting times of forestation is reflected in the present age structure of the forest stands on the eight landholdings studied. The conclusion is drawn that changes in land-use are the major driving force behind the distinct process of forestation that occurred during the 20 th century. Zusammenfassung: In vielen Teilen Europas ist es in den letzten Jahrzehnten zu starken Veränderungen in der Vegetation gekommen. In Norwegen ist die Expansion des Waldes der Haupttrend, mit einer Volumenzunahme auf Landesebene von 20.3% im Zeitraum von 1994 bis 2008, wobei sich die jährliche Zunahme gegenüber 1967 mehr als verdoppelt hat. Ziel der vorliegenden Studie war es, die Komplexität der Vegetationsdynamik und Veränderungen in einem Tieflandbereich an der Westküste Norwegens zu untersuchen und steuernde Faktoren zu identifizieren. Zu diesem Zweck wurde die Vegetation kartiert, Luftbilder interpretiert sowie die Landnutzung für die letzten Jahrhunderte aus historischen Quellen rekonstruiert. Die räumliche Analyse der Daten erfolgte dann GIS-gestützt. Ergänzende Methoden umfassten Bodenanalysen und Dendrochro...

A high-resolution GIS null model of potential forest expansion following land use changes in Norway

“…In local studies, it has been documented that many of the above-mentioned areas have been deforested by various forms of land use lasting for millennias, whereas natural forest regeneration and afforestation in recent decades have evidently shown the ecological potential for forests in semi-natural heaths and meadows throughout Norway (Bryn, 2008;Bryn & Daugstad, 2001;Bryn et al, 2010;Hemsing & Bryn, 2011;Lundberg 2011;Måren, 2009;Moen et al, 2006;Øyen, 2008;Potthoff, 2009;Rö ssler et al, 2008). Similar findings have been reported from local studies in the European Alps and many other mountain regions, so the process of deforestation is probably more or less the same for populated mountain regions worldwide, although with large variations in the extent of deforestation (GehrigFasel et al, 2007;Rutherford et al, 2008;Sitzia et al, 2010;Slaymaker, 2010;Tasser et al, 2007).…”

Traditional land use of the boreal forest landscape: Examples from Lierne, Nord-Trøndelag, Norway

“…Even habitats in remote areas such as inland forests in northern Scandinavia (Ohlson et al 1997) and parts of the Scandinavian mountains (Austrheim & Eriksson 2001) have been utilized for a long time. Currently, regrowth after land use changes is considered to be the major driving force behind the process of forestation in lowland semi-natural vegetation and for the expansion of the forest line upwards (Bryn 2008;Lundberg 2011;Wehn et al 2012). Thus, the distinction between 'undisturbed' and 'disturbed' landscapes is not always clear, but may still be of utmost importance for conservation success.…”

The distribution of the endemic plantPrimula scandinavica, at local and national scales, in changing mountainous environments

“…The modelled response curves indicate that abandonment of the habitats and cessation of domestic grazing will reduce the suitability of the areas. Earlier studies have shown that changes in grazing pressure by domestic animals in mountainous areas in Norway have caused radical vegetation shifts from open semi-natural vegetation to more forested and scrubby areas (Lundberg 2011;Vandvik and Birks 2004;Wehn 2009;Wehn, Olsson, and Hanssen 2012;Wehn, Pedersen, and Hanssen 2011). Livestock grazing supresses taller plant species (Wehn 2009) and thus allows more light for P. scandinavica to persist.…”

“…Norwegian semi-natural habitats have, as in other European countries, decreased due to forest expansion (Lundberg 2011;Vandvik and Birks 2004;Wehn 2009;Wehn, Olsson, and Hanssen 2012;Wehn, Pedersen, and Hanssen 2011). Approximately 40% of the species associated with alpine environments in the Norwegian National Red List are threatened because of changing land use in the alpine region (Austrheim et al 2010).…”