Pollen and charcoal in lake sediments compared with historically documented forest fires in southern Switzerland since AD 1920

Abstract

Charcoal in unlaminated sediments dated by 21"Pb was analysed by the pollen-slide and thin-section methods. The results were compared with the number and area of forest fires on different spatial scales in the area around Lago di Origlio as listed in the wildfire database of southern Switzerland since AD 1920. The influx of the number of charcoal particles > 75 pkm2 in pollen slides correlates well with the number of annual forest fires recorded within a distance of 20-50 km from the coring site. Hence a size-class distinction or an area measurement by image analysis may not be absolutely necessary for the reconstruction of regional fire history. A regression equation was computed and tested against an independent data set. Its use makes it possible to estimate the charcoal area influx (or concentration) from the particle number influx (or concentration). Local fires within a radius of 2 kn around the coring site correlate well with the area influx of charcoal particles estimated by the thin-section method measuring the area of charcoal particles larger than 20 000 gum2 or longer than 50 jim. Pollen percentages and influx values suggest that intensive agriculture and Ca.stanea sativa cultivation were reduced 30-40 years ago, followed by an increase of forest area and a development to more natural woodlands. The traditional Castanea sativa cultivation was characterized by a complete use of the biomass produced, so abandonment of chestnut led to an increasing accumulation of dead biomass, thereby raising the fire risk. On the other hand, the pollen record of the regional vegetation does not show any clear response to the increase of fire frequency during the last three decades in this area.

A continuous record of fire covering the last 10,500 calendar years from southern Sweden — The role of climate and human activities

“…According to most studies on charcoal dispersal and deposition, larger and heavier charcoal fragments settle closer to the fire edge and represent local fires, while smaller, lighter particles may be transported over long distances and, therefore, indicate regional fire events (e.g. Patterson et al, 1987;Whitlock and Millspaugh, 1996;Clark et al, 1998;Long et al, 1998;Tinner et al, 1998;Blackford, 2000;Ohlson and Tryterud, 2000;Carcaillet et al, 2001;Gardner and Whitlock, 2001). Blackford (2000) found that particles b20 μm were most reliable as indicators of regional background charcoal, while particles N125 μm were representative of local fires.…”

“…Moreover, it is known that charcoal deposition may peak several years after the maximum of forest fires, which may blur the detailed fire record (e.g. Whitlock and Millspaugh, 1996;Tinner et al, 1998).…”

“…Millspaugh and Whitlock (1995), Clark et al (1998), and Froyd (2006) suggested that particles N120-125 μm were the most useful to reconstruct fire events. Tinner et al (1998) and Duffin et al (2008) recommended using charcoal N50 μm to reconstruct local fire history.…”

Vegetation and fire history since the last glacial maximum in an inland area of the western Mediterranean Basin (Northern Iberian Plateau, NW Spain)

“…Charcoal concentrations and charcoal accumulation rates (CHAR), which are well-correlated with regional fire activity (Tinner et al, 1998), were estimated using the same approach as for the pollen.…”

“…Thus, pollen analysis is employed as a proxy for vegetation composition and biome type, anthropogenic pollen indicators (Behre, 1981;Brun, 2011) and dung fungal spores (van Geel et al, 2003;Baker et al, 2013) are related to agriculture and grazing, and microscopic charcoal particles are linked to regional fire activity (Tinner et al, 1998). The Northern Iberian Plateau constitutes a perfect study area for tracking human impacts through the last millennia, as it was strongly disturbed by anthropogenic activities.…”