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Constraints on post‐glacial boreal tree expansion out of far‐northern refugia
Author(s) -
Edwards Mary E.,
Armbruster W. Scott,
Elias Scott E.
Publication year - 2014
Publication title -
global ecology and biogeography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.164
H-Index - 152
eISSN - 1466-8238
pISSN - 1466-822X
DOI - 10.1111/geb.12213
Subject(s) - macrofossil , last glacial maximum , pollen , glacial period , boreal , holocene , taiga , range (aeronautics) , ecology , deglaciation , physical geography , geology , geography , biology , paleontology , materials science , composite material
Abstract Aim To use a variety of data sources to infer how northern boreal trees recovered their range upon deglaciation and/or H olocene warming. Location Scandinavia, A laska/north‐west C anada (eastern B eringia). Methods Mapped fossil occurrences for P icea (spruce) were assessed against available palaeoenvironmental and phylogeographic information. Results For S candinavia, L ast G lacial M aximum ( LGM ) evidence of P icea is confined to one DNA record, but late‐glacial and early‐Holocene records include scattered macrofossils. Holocene pollen data show a clear east–west increase to high values. A haplotype unique to the S candinavian P eninsula is recognized. For eastern B eringia pre‐ and post‐ LGM macrofossils occur, but the LGM fossil record comprises only scattered low pollen values. Early H olocene pollen values increase markedly c . 11 cal yr bp (north‐west C anada) and c . 10 kcal yr bp (central A laska). Also at this time three sites on the B ering L and B ridge indicate the presence of P icea where it is now absent. Several unique regional haplotypes were recorded; while most are rare one is common in some modern populations. Main conclusions Small P icea populations probably occurred in pre‐ H olocene S candinavia, but pollen patterns argue against immediate expansion with the onset of warmer conditions. Despite relatively weak fossil evidence, refugial populations are also probable in eastern B eringia, particularly given the extent of unglaciated terrain. Post‐glacial pollen patterns are more nuanced, suggesting two spatially and temporally distinct expansions, one possibly consistent with a unique central A laskan haplotype, and subsequent westerly ‘filling‐in’. The presence of macrofossils and/or neutral markers does not require that current northern populations are derived primarily from refugial ones, particularly where pollen patterns show delayed directional expansion of large populations though time. Refugial populations initially responded weakly to major post‐glacial environmental change; if subject to genetic isolation and strong selection pressure they may have had little potential to do otherwise, instead being largely replaced by in‐migrating populations with greater genetic diversity.