Climate continentality and treeline species distribution in the Alps

Abstract

The distribution of tree species and the elevation of the alpine treeline are strongly affected by climate continentality. In the present work we performed a detailed survey of the upper limits of tree vegetation in two areas with contrasting climate located in the central Italian Alps, in order to evaluate the structure of the treeline under different degrees of continentality. Tree and krummholz (stunted) individual position, their dimension and life form were recorded from the upper limit of the closed forest to the species limit. The results were compared with an estimation of tree species distribution at the treeline in the whole Lombardy Alps, performed by a survey of tree species occurrence in areas of known climatic traits. The structure of the treeline (upper limits, life form altitudinal arrangement) and its ongoing dynamics were different in the two areas: climate continentality assessed by hygric and thermal continentality indices influenced the distribution of some treeline species. Although the influence of human and geomorphologic disturbance could not be excluded, the importance of the degree of continentality must be stressed when evaluating the response of the treeline to past and present climatic change.

A comparison between different treeline types shows contrasting responses to climate fluctuations

“…Growth season temperatures are widely considered the main factor affecting the position of both latitudinal and altitudinal treelines (Tranquillini 1979;Körner 1998;Körner & Paulsen 2004;Körner & Hoch 2006); however, also the role of winter temperatures and of precipitation regimes has proved to be critical (Jobbagy & Jackson 2000;Camarero & Gutierrez 2004;Bader et al 2007;Caccianiga et al 2008;Harsch et al 2009;Kharuk et al 2010). Körner (1998Körner ( , 2008 Successive statistical modelling confirmed data from in situ measurements suggesting a minimum growth season temperature of 6.4°C globally (Paulsen & Körner, 2014).…”

“…In our case, a lack of recruitment seems to be important, which can be due to high seedling mortality, low germination rates or to a less effective dispersal strategy of Larix decidua compared with zoochorous Pinus cembra (Holtmeier & Broll 2007;Lingua et al 2008). Species composition seems to be determining for treeline behaviour, and is probably linked to climatic continentality, Pinus cembra being less adapted to relatively oceanic climates (Theurillat & Schlüssel 2000;Caccianiga et al 2008). The overall low density of the population may also play a role.…”

Climate Warming and the Recent Treeline Shift in the European Alps: The Role of Geomorphological Factors in High-Altitude Sites

“…The study area is in the western Italian Alps, an area where the Alpine mountain range represents a barrier to the warmer and wetter air masses coming from the Atlantic Ocean carried by the western winds. Here the climate is semi-continental and treelines grow at higher altitudes than in areas characterized by more oceanic conditions (Caccianiga et al 2008). In this region, the treelines are mainly constituted by the European larch (Larix decidua L.), a widespread species in the European Alps adapted to poor and shallow soils, which has a wind-dispersed strategy for seeds.…”

Spatial Interpolation of Ewert’s Index of Continentality in Poland

“…Recently, continentality indices have been applied in environmental analyses, particularly as a variable supporting the analysis of variability and spatial distribution of, e.g., air temperature (Hogewind and Bissolli 2011), evapotranspiration (Marti and Gasque 2010) and bioclimatic changes (Torregrosa et al 2013). The analytical usefulness of continentality indices has also been corroborated in the investigations of glacier mass balance (Holmlund and Schneider 1997), plant species range and the treeline (Caccianiga et al 2008), and plant pollen in northern Europe (Salonen et al 2012).…”