Changes in landscape structure in the northwestern Alps over the last 7000 years: lessons from soil charcoal

Abstract

Abstract. Current land‐use a bandonment and the current rise in temperature in the Alps both suggest that tree limits may change. When it is assumed that the climate of the early mid‐Holocene between 8000 and 5000 yr before present is analogous to that of the predicted climate of the late 21st century, palaeo‐ecological studies of the early Holocene may provide data for the prediction of the vegetation pattern in a century from now. It appears that mid‐Holocene charcoal assemblages can be used to reconstruct the spatial patterns of the vegetation before, or during, the practice of slash‐and‐burn. Correspondence analysis (CA) of charcoal assemblages shows that an important ecological gradient is determined by elevation. However CA also shows that charcoal assemblages in profiles between 1700 and 2100 m a.s.l. are roughly stratified: the more recent assemblages from the topmost centimetres of soil are intermediate between the lowermost assemblages and assemblages from higher elevations. This suggests that the woody communities at the highest elevation were located at lower elevations at a later date. The taxonomic diversity of the soil charcoal assemblages has been compared to that of present‐day phytosociological relevés after transformation to charcoal‐equivalent data. This comparison revealed that the vegetation pattern along the altitudinal gradient in the mid‐Holocene was different from that at present. The assemblages indicate that some communities disappeared, that Picea is a late‐Holocene invading species, and that there is no strict modern analogue for the vegetation structure prior to that of 3000 yr ago. The past structure of the woody vegetation was also different from that of today. Although past vegetation is not a good analogue for predicting future vegetation patterns, it still has potential as an indicator for the potential presence of tree species where there is none today. If we assume a temperature rise, and take into account current trends of landscape use abandonment, then we can expect strong vegetation dynamics at the upper tree line in the future: Abies alba may expand to occupy elevations of ca. 1800–2000 m in mixed communities with Picea abies, Pinus sylvestris and hardwood species, and Pinus cembra may expand up to 2500–2700 m a.s.l.

Patterns of plant traits in Pyrenean alpine vegetation

“…A notable part of the alpine landscape is subjected to non-equilibrium situations, species replacements may therefore involve substantial shifts in coarse vegetation structure and ecosystem function. Several examples of these shifts, caused by Quaternary climatic changes, have been documented from soil and lacustrine sediments over the last millenia (Blinnikov 1994;Carcaillet and Brun 2000;Montserrat 1992;Tinner and Theurillat 2003). The present coupling of climatic change and pasture abandonment is expected to contribute to further strong shifts.…”

Disturbance history and dynamics of an old-growth mixed species mountain forest in the Slovenian Alps

“…The present structure and composition of these forests are largely a result of these past activities (Ott et al, 1997;Carcaillet and Brun, 2000;Motta and Edouard, 2005). Currently, there is interest in restoring the structure and composition of some forests towards pre-settlement conditions (Mayer and Ott, 1991;Schö nenberger, 2001), especially in forest reserves or managed forests where silvicultural prescriptions should mimic natural mortality processes (Coates and Burton, 1997;Seymour et al, 2002;Hanson and Lorimer, 2007).…”

Distinguishing subalpine soil types using extractible Al and Fe fractions and REE geochemistry

“…6000 years BP (Carcaillet, 1998;David and Barbero, 2001). Studies indicate that subalpine grasslands have succeeded the former cembra pine forests (Carcaillet and Brun, 2000), resulting in a reduced elevation of the upper treeline (Carcaillet and Muller, 2005). At the present day, subalpine grassland soils developed on Carboniferous formations with similar elevation and aspect are dominated by Cambisols (WRB, 2006), whereas soils under relatively undisturbed old-growing subalpine coniferous forests are characterized by Podzols.…”