The Holocene treeline in the northern Andes (Ecuador): First evidence from soil charcoal

Abstract Background: The present article questions the relative importance of local- and large-scale processes on the long-term dynamics of fire in the subalpine belt in the western Alps. The study is based on soil charcoal dating and identification, several study sites in contrasting environmental conditions, and sampling of soil charcoal along the elevation gradient of each site. Based on local differences in biomass combustion, we hypothesize that local-scale processes have driven the fire history, while combustion homogeneity supports the hypothesis of the importance of large-scale processes, especially the climate. Results: The results show that biomass burning during the Holocene resulted from the nesting effects of climate, land use, and altitude, but was little influenced by topography (slope exposure: north versus south), soil (dryness, pH, depth), and vegetation. The mid-Holocene (6500–2700 cal BP) was an important period for climatic biomass burning in the subalpine ecosystems of the western Alps, while fires from about 2500 years ago appear much more episodic, prompting us to speculate that human society has played a vital role in their occurrence. Conclusion: Our working hypothesis assuming that the strength of mountain natural and local drivers should offset the effects of regional climate is not validated. The homogeneity of the fire regime between sites thus underscore that climate was the main driver during the Holocene of the western Alps. Long-term subalpine fires are controlled by climate at millennial scale. Local conditions count for little in determining variability at the century scale. The mid-Holocene was a chief period for climatic biomass burning in the subalpine zone, while fires during the late Holocene appear much more episodic, prompting the assumption that societal drivers has exercised key roles on their control.

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11 000 years of fire history and climate in the mountain hemlock rain forests of southwestern British Columbia based on sedimentary charcoal

Canadian Journal of Forest Research ◽

10.1139/x02-177 ◽

2003 ◽

Vol 33 (2) ◽

pp. 292-312 ◽

Cited By ~ 95

Author(s):

Douglas J Hallett ◽

Dana S Lepofsky ◽

Rolf W Mathewes ◽

Ken P Lertzman

Keyword(s):

British Columbia ◽

Lake Sediment ◽

Fire History ◽

Fire Regime ◽

Fire Frequency ◽

Summer Drought ◽

Rain Forests ◽

Independent Evidence ◽

The Holocene ◽

Soil Charcoal

Little is known about the role of fire in the mountain hemlock (Tsuga mertensiana (Bong.) Carrière) rain forests of southern British Columbia. High-resolution analysis of macroscopic charcoal from lake sediment cores, along with 102 accelerator mass spectrometry (AMS) ages on soil charcoal, was used to reconstruct the long-term fire history around two subalpine lakes in the southern Coast and North Cascade Mountains. AMS ages on soil charcoal provide independent evidence of local fire around a lake and support the interpretation of peaks in lake sediment charcoal as distinct fire events during the Holocene. Local fires are rare, with intervals ranging from centuries to several millennia at some sites. Overall fire frequency varied continuously throughout the Holocene, suggesting that fire regimes are linked to climate via large-scale atmospheric circulation patterns. Fires were frequent between 11 000 and 8800 calendar years BP during the warm and dry early Holocene. The onset of humid conditions in the mid-Holocene, as rain forest taxa established in the region, produced a variable fire period until 3500 calendar years BP. A synchronous decrease in fire frequency from 3500 to 2400 calendar years BP corresponds to Neoglacial advances in the region and cool humid climate. A return of frequent fire between 2400 and 1300 calendar years BP suggests that prolonged summer drought occurred more often during this interval, which we name the Fraser Valley Fire Period. The present-day fire regime was established after 1300 calendar years BP.

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Soil charcoal stability over the Holocene across boreal northeastern North America

Quaternary Research ◽

10.1016/j.yqres.2011.06.006 ◽

2011 ◽

Vol 76 (2) ◽

pp. 196-200 ◽

Cited By ~ 20

Author(s):

Guillaume de Lafontaine ◽

Hugo Asselin

Keyword(s):

North America ◽

Residence Time ◽

Fire History ◽

Mineral Soil ◽

Forest Composition ◽

Northeastern North America ◽

The Holocene ◽

Soil Charcoal ◽

Biogeographical Regions ◽

The Relationship

AbstractThe analysis of macroscopic wood charcoal fragments extracted from soils is frequently used as a palaeoecological tool for reconstructing stand-scale forest composition and fire history. Here we explored the putative loss of palaeoecological information due to charcoal degradation through time and in different biogeographical settings. We compared the relationship between charcoal mass and abundance for soil samples from five biogeographical regions of boreal northeastern North America spanning most of the Holocene period. We verified whether charcoal (Ø ≥ 2 mm) conservation differed as a consequence of different taphonomical processes between organic and mineral soil types. We also assessed the mass/abundance relationship as a function of charcoal residence time in soil. Overall, the slope of the regression between charcoal particles mass (g) and abundance (number of particles) was 0.0042. The slope was not significantly different in samples from organic and mineral soil, and all biogeographical regions had similar slope values except one (higher charcoal fragmentation, probably due to high colluvial activity). Charcoal conservation also did not vary according to residence time in soil. This study shows that macroscopic soil charcoal particles resist fragmentation over millennia in different biogeographical settings and under the influence of various taphonomical processes.

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