Within-tree fluctuating asymmetry of mountain birch in subarctic Sweden

Abstract: The mountain birch ecosystem forms the northern treeline in subarctic Europe. Since the treeline isextremely sensitive to temperature, stress in mountain birch can be used as an indicator of stress onthe ecosystem as a whole, and in predictions of how climate change factors will influence thesubalpine-tundra ecotone and treeline dynamics. Fluctuating asymmetry (FA) is a commontechnique for assessing stress in mountain birch. While no previous research has studied withintreevariations of FA in mountain birch, other species have shown significant variation dependingon location of the leaf within the crown, and thus leaf collection location is important to considerwhen sampling. The objective of this study is to determine if a relationship exists between leaf FAand location within the tree crown of mountain birch leaves across three elevation zones insubarctic Sweden. Leaves were collected from various locations within the crown with regards toheight (bottom, middle, top), direction (north, east, south, west), and position (inner, outer), and at3 elevation sites (valley, forest-limit, treeline). A nested ANOVA was used to analyze the data.The treeline site showed a higher amount of FA than the valley or forest-limit sites (P = 0.0228),but no significant difference was found between any of the within-tree leaf locations. This suggeststhat there is no influence from crown location on FA in the leaves of mountain birch, and thereforefuture studies involving FA can freely sample leaves from any location within the crown.