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The role of fire in the mid-Holocene arrival and expansion of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) in Yukon, Canada

The role of fire in the mid-Holocene arrival and expansion of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) in Yukon, Canada
The role of fire in the mid-Holocene arrival and expansion of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) in Yukon, Canada
In north-west Canada, Pinus contorta (lodgepole pine) has been migrating northwards and westwards for millennia. Its regeneration is currently enhanced by fire, which may act as a trigger for local population expansion. Using Holocene charcoal records from four small (<10 ha) lakes in southern Yukon, we investigated the relationship between long-term Pinus population dynamics and fire. Fossil stomata extracted from dated lake sediments indicate pine was present at low densities in southern Yukon forests by ~6000 cal. yr BP. At each site, the main population expansion (indicated by an increase in Pinus pollen from <5% to values as high as 60%) occurred 2000–>4000?years after the first local appearance of Pinus, suggesting a long period of stasis at low densities. Population increases – based on pollen accumulation rates (PARs) – occurred at different times at the four sites. Estimated expansion periods were ~2500–800?years, and population doubling times were ~150–600?years, similar to previous estimates. Estimated fire return intervals (FRIs) fluctuated over time. At all sites, the Pinus expansion began during a phase with a relatively short FRI, but only one difference between the mean FRIs before and during the Pinus rise was statistically distinguishable. Nor was the subsequent higher abundance of pine associated with shorter FRIs. It is unlikely that regional pine expansion is primarily linked to changes in climate or a climate-mediated fire regime, although expansion may have been triggered at individual sites during a period of high fire frequency. The long period of stasis at low population densities suggests intrinsic control of population growth; possibly Pinus expansion was initially constrained by lowered reproductive fitness (Allee effect) and/or interaction with local site-based factors
0959-6836
64-78
Edwards, Mary E.
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Franklin-Smith, L.M.
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Clarke, C.
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Baker, J.
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Hill, S.
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Gallagher, K.
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Edwards, Mary E.
4b6a3389-f3a4-4933-b8fd-acdfef72200e
Franklin-Smith, L.M.
529e32b5-0181-4dd3-ab78-187df61eaad7
Clarke, C.
68afb5e9-7966-4b54-9549-47c49e350f6c
Baker, J.
bf383151-af5c-4783-8f9b-7bff94043354
Hill, S.
84cd4c7d-ceee-4ae2-b4cf-a2517e49aded
Gallagher, K.
ff25a7df-39f2-45bb-9960-5b594e6cc245

Edwards, Mary E., Franklin-Smith, L.M., Clarke, C., Baker, J., Hill, S. and Gallagher, K. (2015) The role of fire in the mid-Holocene arrival and expansion of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) in Yukon, Canada. The Holocene, 25 (1), 64-78. (doi:10.1177/0959683614556389).

Record type: Article

Abstract

In north-west Canada, Pinus contorta (lodgepole pine) has been migrating northwards and westwards for millennia. Its regeneration is currently enhanced by fire, which may act as a trigger for local population expansion. Using Holocene charcoal records from four small (<10 ha) lakes in southern Yukon, we investigated the relationship between long-term Pinus population dynamics and fire. Fossil stomata extracted from dated lake sediments indicate pine was present at low densities in southern Yukon forests by ~6000 cal. yr BP. At each site, the main population expansion (indicated by an increase in Pinus pollen from <5% to values as high as 60%) occurred 2000–>4000?years after the first local appearance of Pinus, suggesting a long period of stasis at low densities. Population increases – based on pollen accumulation rates (PARs) – occurred at different times at the four sites. Estimated expansion periods were ~2500–800?years, and population doubling times were ~150–600?years, similar to previous estimates. Estimated fire return intervals (FRIs) fluctuated over time. At all sites, the Pinus expansion began during a phase with a relatively short FRI, but only one difference between the mean FRIs before and during the Pinus rise was statistically distinguishable. Nor was the subsequent higher abundance of pine associated with shorter FRIs. It is unlikely that regional pine expansion is primarily linked to changes in climate or a climate-mediated fire regime, although expansion may have been triggered at individual sites during a period of high fire frequency. The long period of stasis at low population densities suggests intrinsic control of population growth; possibly Pinus expansion was initially constrained by lowered reproductive fitness (Allee effect) and/or interaction with local site-based factors

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Accepted/In Press date: 24 September 2014
Published date: January 2015
Organisations: Palaeoenvironment Laboratory (PLUS)

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Local EPrints ID: 377217
URI: http://eprints.soton.ac.uk/id/eprint/377217
ISSN: 0959-6836
PURE UUID: a98063fb-44e2-478b-9abe-d21442fad9d3
ORCID for Mary E. Edwards: ORCID iD orcid.org/0000-0002-3490-6682

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Date deposited: 28 May 2015 10:22
Last modified: 15 Mar 2024 03:13

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Contributors

Author: Mary E. Edwards ORCID iD
Author: L.M. Franklin-Smith
Author: C. Clarke
Author: J. Baker
Author: S. Hill
Author: K. Gallagher

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