Responses of white spruce (Picea glauca) to experimental warming at a subarctic alpine treeline

Abstract

From 2001 to 2004 we experimentally warmed 40 large, naturally established, white spruce [Picea glauca (Moench) Voss] seedlings at alpine treeline in southwest Yukon, Canada, using passive open-top chambers (OTCs) distributed equally between opposing north and south-facing slopes. Our goal was to test the hypothesis that an increase in temperature consistent with global climate warming would elicit a positive growth response. OTCs increased growing season air temperatures by 1.8 1C and annual growing degree-days by one-third. In response, warmed seedlings grew significantly taller and had higher photosynthetic rates compared with control seedlings. On the south aspect, soil temperatures averaged 1.0 1C warmer and the snow-free period was nearly 1 month longer. These seedlings grew longer branches and wider annual rings than seedlings on the north aspect, but had reduced Photosystem-II efficiency and experienced higher winter needle mortality. The presence of OTCs tended to reduce winter dieback over the course of the experiment. These results indicate that climate warming will enhance vertical growth rates of young conifers, with implications for future changes to the structure and elevation of treeline contingent upon exposure-related differences. Our results suggest that the growth of seedlings on north-facing slopes is limited by low soil temperature in the presence of permafrost, while growth on south-facing slopes appears limited by winter desiccation and cold-induced photoinhibition.

Belowground responses of Picea asperata seedlings to warming and nitrogen fertilization in the eastern Tibetan Plateau

“…The effects of warmer climate on aboveground forest ecosystems have already been studied with various techniques (Farnsworth et al 1995;Luxmoore et al 1998;Yin et al 2008;Danby and Hik 2007). However, a few studies have been conducted in situ on the effects of soil warming on belowground forest ecosystems, including the root growth and rhizosphere soil processes, using heating cables (Van Cleve et al 1990;Majdi and Ö hrvik 2004), *P < 0.05, ** P < 0.01, *** P < 0.001, NS not significant (significant difference between treatments) Dependent variable: total biomass.…”

Population Spatial Dynamics of Larix potaninii in Alpine Treeline Ecotone in the Eastern Margin of the Tibetan Plateau, China

“…In our study, Larix recruitment was strongly correlated with temperature in winter or early growing seasons, which was also observed in the Tianshan Mountains, Northwestern China [11]. Warmer winter will lead to higher soil temperature and longer snow-free periods, which could increase the vertical growth of trees [34,47]. A global model of the treeline claimed that the general critical value of mean daily temperature for the onset of wood formation was 8-9 • C [4].…”

“…For the north-facing slopes in eastern TP, treeline dynamics and recruitment appears to be limited by lower soil temperature and a short growing period [34]. In winter, the thicker snow cover on north-facing slopes could prevent winter stress by insulating root and plant tissues from wind damage, frost, and abrasion, which provides snow protection for individuals in winter [20].…”

“…Toward the treeline, the environment becomes much more stressful, so individuals tend to be clustered because there are fewer places that plants can grow successfully [42]. Therefore, climate warming will allow seedlings and saplings to more rapidly achieve a canopy height sufficient enough to withstand the negative effects when extending toward the treeline [34], providing the potential for future treeline advance; however, other limiting factors such as precipitation, topography, and wind exposure also need to be considered.…”

Study of the active layer at the Spanish Antarctic station “Gabriel de Castilla”, Deception Island, Antarctica

“…de . Análisis del estado de la capa activa en el emplazamiento… Boletín Geológico y Minero, 128 (1): 69-92 más cerca de la misma (ej., Zhang, 2005;Danby y Hik, 2007;Lewkowicz, 2008;Gadek y Leszkiewicz, 2010). Estos mismos datos son empleados para el cálculo de la temperatura máxima, media y mínima anual para cada profundidad, pudiendo realizarse perfiles de gradiente de temperatura que permiten determinar la profundidad del techo del permafrost (por definición, la profundidad a la cual la curva de la temperatura máxima anual sobrepasa la isoterma de los 0ºC), o su aproximación mediante la interpolación y extensión en profundidad de la curva de las temperaturas máximas anuales (ej.…”