Potential for Timberline Advance in Northern Finland, as Revealed by Monitoring during 1983-99

Abstract

ABSTRACT. Seedling density, tree density and basal area of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) were monitored and compared in the timberline areas of northern Finland during the period 1983-99. Rows of 9-12 circular plots were established at 13 localities in four regions: pine-dominated northern and southern regions and spruce-dominated western and eastern regions. Temporal changes were monitored in three altitudinal zones: in the forest, at the coniferous timberline (where forest canopy closure ceases), and at the tree line (where coniferous trees higher than 2 m cease). Pine seedling densities decreased abruptly in the southern region, especially at the timberline, but increased slightly in the northern region. The zone · region · change interaction was significant. The change in spruce seedling densities was small in the forest and timberline zones, but the densities more than doubled at the tree line. Tree density and basal area increased in all the zones and regions. New regeneration and tree establishment during the study period indicate a potential for the tree line to advance. However, there was great heterogeneity in regeneration and seedling establishment among the localities.Key words: climate change, climatic variation, regeneration, Pinus sylvestris, Picea abies, seedling density, tree density, basal area, timberline, tree line RÉSUMÉ. La densité des semis, la densité des arbres et la surface terrière du pin sylvestre (Pinus sylvestris L.) et de l'épinette de Norvège (Picea abies [L.] Karst) ont fait l'objet d'une étude et d'une comparaison dans des zones situées à la limite de la forêt de la Finlande septentrionale durant la période allant de 1983 à 1999. Des rangées de 9 à 12 parcelles circulaires ont été créées à 13 sites répartis dans 4 zones: les régions septentrionale et méridionale où dominait le pin sylvestre, et les régions occidentale et orientale où dominait l'épinette de Norvège. On a mesuré les changements temporels dans 3 zones d'altitude différente: dans la forêt, à la limite de la forêt de conifères (là où cesse la fermeture du couvert forestier), et à la limite des arbres (là où cessent les conifères de plus de 2 m de haut). La densité de semis du pin sylvestre diminuait brusquement dans la région méridionale, en particulier à la limite de la forêt, mais elle augmentait légèrement dans la région septentrionale. L'interaction zone-région-changement était significative. Le changement dans la densité de semis de l'épinette de Norvège était faible dans la forêt ellemême et dans les zones de la limite de la forêt, mais la densité avait plus que doublé à la limite des arbres. La densité des arbres et la surface terrière augmentaient dans toutes les zones et les régions. Une nouvelle régénération et un nouvel établissement d'arbres durant la période d'étude révèlent que la limite des arbres pourrait progresser. Il y avait toutefois une grande hétérogénéité dans la régénération et dans l'établissement des semis parmi les divers sites.

Natural regeneration of Scots pine and Norway spruce close to the timberline in northern Finland

“…The present paper deepens the analyses of an earlier study (Juntunen et al 2002) by focusing on small seedlings (< 20 cm) and including data on seedling mortality in the analyses. In addition, data on seed maturation of Scots pine in relation to summer temperatures in the northern timberline (where forest canopy closure ceases) and tree line (beyond which coniferous trees taller than 2 m no longer exist) is presented.…”

“…Responses of different models vary from drastic positive effects on boreal forests and the coniferous timberline (Kellomäki andVäisänen 1995, Kellomäki et al 1997) to catastrophic incidents of dieback and regression of the timberline (Gates 1990, Hänninen 1991, Juday et al 1997. Recent studies show that tree species respond individualistically to climatic variation (Brooks et al 1997, Kullman 2001, Juntunen et al 2002. Moreover, the responses are often regionally variable in magnitude and direction (Kullman 2001, Juntunen et al 2002.…”

“…Recent studies show that tree species respond individualistically to climatic variation (Brooks et al 1997, Kullman 2001, Juntunen et al 2002. Moreover, the responses are often regionally variable in magnitude and direction (Kullman 2001, Juntunen et al 2002. Follow-up measurements on permanent plots since 1983 in Finnish Lapland have revealed that regeneration of Norway spruce (Picea abies (L.) Karst.)…”

“…Follow-up measurements on permanent plots since 1983 in Finnish Lapland have revealed that regeneration of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) has occurred in climatically extreme areas during recent decades suggesting that advancement of timberlines may occur in the near future (Juntunen et al 2002).…”

Annual cycle of Scots pine photosynthesis

“…These large variations in light and temperature are greatly influencing the distribution of plant species, especially in the northern regions. As an example, Scots pines (Pinus sylvestris L.), while abundant all over Europe, have also adapted especially well to the annual cycle of radiation and temperature in the northern climate, forming even the treeline in many regions (Juntunen et al, 2002).…”