The Holocene history of low altitude Mediterranean Fagus sylvatica forests in southern France

Abstract

Questions As the dominant tree in many European forests, Fagus sylvatica functions as an ecosystem engineer, yet its istory remains little understood. Here we ask: (a) are there indications for its presence in southeast France during the last Glacial period; (b) what was the timing of the expansion and decline of F. sylvatica dominated forests; (c) which factors influenced their dynamics and in particular to what extent did past precipitation changes impact upon them; and (d) at which altitudes did these beech forests occur within the region? Location Languedoc, the French Mediterranean area. Method This article presents a well dated and high‐resolution pollen sequence covering the last 7,800 years from the Palavas Lagoon in the Languedoc together with a review of Fagus charcoal occurrences in the Languedoc and the lower Rhône Valley, and a review of pollen data from a compilation of 69 sites in southeast France. Results The Palavas pollen sequence provides a regional summary of F. sylvatica abundance changes near the Mediterranean coast. Around 6,000 years cal BP, an abrupt transition from small beech populations to well‐developed forests is recorded. The maximum development of beech forests occurred between 4,000 and 3,000 years cal BP, while F. sylvatica started to regress after 3,000 years cal BP. Conclusion Scattered F. sylvatica populations probably survived throughout southern France during the last Glacial period. F. sylvatica started to spread around 8,000 years cal BP while beech forests never expanded before 6,000 years cal BP. The complex patterns of F. sylvatica expansion in southern France after 6,000 years cal BP suggests that a combination of global (climate change) and local (human impact) factors were responsible for this major change. Recurrent abrupt climate changes, the aridity trend and human deforestation caused beech forests to decline after 3,000 years cal BP.

Mid- to Late-Holocene Mediterranean climate variability: Contribution of multi-proxy and multi-sequence comparison using wavelet spectral analysis in the northwestern Mediterranean basin

“…Pollen concentration was estimated by adding a known amount of Lycopodium spores. Pollen grains were counted and identified at 400x and 1000x amplification, respectively, with reference to pollen keys, atlases and comparison with a reference collection (Azuara et al 2015(Azuara et al , 2018.…”

“…Thus, both taxa are particularly sensitive to climate fluctuations. Decreases (increases) in pollen proportions of these two taxa synchronous with increases (decreases) in deciduous Quercus proportions have been interpreted as repetitive mountainous forest retreats toward higher altitudes coinciding with repeated expansions of deciduous Quercus at lower altitudes during dry events (Azuara et al 2015(Azuara et al , 2018. The covariations of these taxa are summarized within a single indicator called "Aridity index" ( !…”

Holocene land cover and population dynamics in Southern France

“…Southern France also possesses a large number of pollen records for reconstructing past land-cover. Although several reviews have tried to decipher the causes of long-term Mediterranean vegetation change, there is still no clear understanding of the respective role of past human activities and climate in vegetation change (Azuara et al, 2015(Azuara et al, , 2018de Beaulieu et al, 2005;Jalut et al, 2000Jalut et al, , 2009. This is partly due (a) to the chronology (age-depth models), which is still a limiting factor when comparing several pollen records, (b) to the definition of similarities and differences in vegetation patterns when exploring multiple pollen records and (c) to the difficulties of relating them to independent climatic and population proxies.…”

Millennial to centennial vegetation change

“…The first documents dramatic vegetation changes caused by European farmers in Australia's Kimberley region during the 19–20th centuries, calibrated using modern surface samples (Connor et al., ). The second study, mainly based on a single site, focuses on the history of beech forests in Mediterranean France (Azuara, Lebreton, Peyron, Mazier, & Combourieu‐Nebout, ). By reviewing additional palaeoecological studies Azuara et al.…”

“…By reviewing additional palaeoecological studies Azuara et al. () show that beech‐dominated forests were common near the Mediterranean coast at elevations as low as 200 m, and only disappeared with land‐use changes around 1,500 years ago. In the final contribution to this special feature Brussel, Minckley, Brewer, and Long () convert a Holocene pollen diagram from the north‐western USA into functional traits of the past vegetation, and find that temporal changes in some functional attributes can be related to changes in fire frequency.…”