Changes in radial tree growth for Picea abies, Larix decidua, Pinus cembra and Pinus uncinata near the alpine timberline since 1750

Abstract

Changes in radial growth of the four coniferous species growing in the French Alps near the upper treeline are investigated. Thirty-seven populations of Norway spruce [Picea abies (L.) Karst.], European larch (Larix decidua Mill.), Swiss stone pine (Pinus cembra L.) and mountain pine (Pinus uncinata Mill. ex Mirb.)were sampled by taking 1320 cores and analysing treering widths. Sites were chosen in various climatic conditions (macroclimate and aspect) and on two kinds of bedrock in order to take into account the ecological behaviour of these species. Belledonne, Moyenne-Tarentaise, Haute-Maurienne and Briançonnais areas were sampled along increasing gradients of summer aridity and winter continentality. The calculation of time series after removing the age trend brings strong evidence for an increase in radial growth during the two last centuries, but with different stages and fluctuations for each species. This growth trend is significantly enhanced since 1860 for the spruce, and since 1920 for the two pine species. Furthermore, it also appears on Larix decidua with the same pattern despite periodical growth reduction due to attacks of the larch bud moth (Zeiraphera diniana Gn.). The analysis of ring-widths at a given cambial age reveals that this enhanced phenomenon is observed especially during the tree's early years (25-75 years). The analysis of four regional climatic series, and three longer series of temperature (in farther single sites) reveals synchronous decadal fluctuations and an evident secular increase in minimum temperatures (especially in January and from July to October), that may be involved in treegrowth enhancement. Thermic amplitudes are significantly reduced during the whole growing period, what is more pronounced in Belledonne, the most oceanic region. Long term growth changes are well described by stepwise regression models, especially for the pine species. These models involved both a linear trend (CO 2 concentration or N-deposition) and low frequency of Turin monthly temperatures. However, they show different patterns than those observed from response functions at a yearly scale.

Human land-use, forest dynamics and tree growth at the treeline in the Western Italian Alps

“…they receive less light because of the canopy cover and face fiercer competition at the ground and root level. In fact, under similar conditions in the Val Varaita similar results emerged [40], while in other areas of the Alps, various authors [4,42,48] have found growth rate increases that affected all age classes. However accurately interpreting trends in tree ring series and cambial age-stratified data is neither simple nor unequivocal, especially since the data is subject to numerous methodological biases [27,40].…”

“…The growth of small trees (h < 3 m) at the treeline may respond differently to climate than taller trees [19,33] but, in the study area, the growth change has been observed in the same time in individuals of different height (0.5-3 m) and of different age (> 40 years of age range) representing the occurrence of an "event" more than a "trend" [50]. Besides microclimate associated with microsite could control growth during the early stages of tree development [32,48] but the study site has a very regular slope and morphology and microsite influence is low.…”

“…A smaller number of studies, however, have also shown that these limits are relatively stable [25]. In the same time tree-growth increments at the tree-* Corresponding author: renzo.motta@unito.it line have been observed in many mountains around the world [20,27,44,45,48].…”

Complex climate constraints of upper treeline formation in the Pyrenees

“…Radial growth enhancement has been observed in many treelines being mostly attributed to warmer temperatures (Rolland et al 1998;Camarero and Gutiérrez 2004;Salzer et al 2009). …”

Climatic factors affecting the tree‐ring width of Betula ermanii at the timberline on Mount Norikura, central Japan

“…Thus, the growth is a useful indicator to examine how climatic conditions affect regeneration of trees at the timberlines. Although many researchers investigated the effects of climatic conditions on the tree growth at the timberlines in North America and Europe (e.g., Kienast et al 1987;Rolland et al 1998;Szeicz & MacDonald 1995;Paulsen et al 2000;Carrer & Urbinati 2004), there are few studies reported in Japan. Increased knowledge of the climate-growth relationships at the timberlines is of great importance for understanding the effects of global warming on the tree regeneration at the timberlines, especially in Japan, where there are many high mountains.…”