Treeline (Pinus sylvestris) landscape evolution in the Swedish Scandes – a 40-year demographic effort viewed in a broader temporal context

Figures & data

Fig. 1. Location of the study area and the permanent plots (circles) and the pine treeline in the Handölan valley by the early 20th century, according to Kullman (1981) (line with filled black circles)

Fig. 2. Annual records of winter (December–February) (upper graph) and summer (June–August) (lower graph) mean temperatures from Storlien-Visjövalen weather station

Fig. 3. Evolution of the pooled population size (all 18 plots) during the period 1973–2012

Table 1. Summer and winter air temperatures (°C ± SD) for periods with different population trends

Period	Summer (June, July, August)	Winter (December, Janauary, February)	Trend
1973–1987	10.1 ± 0.8	−7.5 ± 2.4	Decline
1988–2005	10.8 ± 1.3	−5.3 ± 1.1	Increase
2006–2012	11.1 ± 1.1	−6.0 ± 3.4	Decline

Fig. 4. Recruitment (upper bar chart) and mortality (lower bar chart) expressed as the number of pines during a specific year

Fig. 5. Annual minimum soil temperature (upper graph) and maximum soil temperatures (lower graph)

Fig. 6. Annual laboratory tests of pine seed germinability

Fig. 7. Annual assessment of the frequency of pines (18 plots) that had suffered more than 20% defoliation (winter desiccation)

Fig. 8. Upper: one of the permanent plots with a dense sapling population, severely impacted by winter desiccation during the winter of 1994–1995 (Photo: Leif Kullman, 15 July 1995); Lower: young pines that had grown substantially in height and that had recovered almost completely by 2013 (Photo: Leif Kullman, 28 January 2013)

Fig. 9. A pine (Pinus sylvestris) sapling outside the permanent plots, displaying characteristically unusually long and vital needles (Photo: Leif Kullman, 7 May 2004)

Fig. 10. Upper: permanent plot centred on a mature pine that germinated in the 1830s (Photo: Leif Kullman, 16 March 1983); Lower: the monitored increase in the pine populations' height and density in the study period (Photo: Leif Kullman, 28 January 2013)

Fig. 11. Upper: permanent plot with a few low-growing saplings surrounding a putative ‘mother’ tree (Photo: Leif Kullman, 21 April 1985); Lower: the stand expanded in terms of size and number of individuals since 1985 (Photo: Leif Kullman, 28 January 2013)

Fig. 12. Upper: the southernmost pine stand in the Handölan valley (690 m a.s.l.) by the early 20th century (Photo: Harry Smith, 12 April 1914); Lower: trees and saplings that had increased within the circumference of the old trees by 2013 (Photo: Leif Kullman, 29 January 2013)

Fig. 13. Solitary pine tree (840 m a.s.l.) representing treeline shift 10 km southwards down the Handölan valley and 140 m upslope since the early 20th century; coring at the ground-level dury the study indicated that the pine germinated in the late 1930s (Photo: Leif Kullman, 24 April 2011)

Fig. 14. Pine forest limit in the Handölan valley, which has remained virtually stable since the early 20th century except for densification and increased vigour (Kullman 1986) (Photo: Leif Kullman, 18 February 2013)

Fig. 15. Pine tree remnant located above the present-day tree line (during the Medieval Warm Period); Mt. Täljstensvalen in the Handölan Valley, 770 m a.s.l. (Photo: Leif Kullman, 9 September 2012)