A Pleistocene Clone of Palmer's Oak Persisting in Southern California

Michael R May,Norman C Ellstrand,Andrew C Sanders,Mitchell C Provance,Jeffrey Ross-Ibarra,Edward Newbigin

doi:10.1371/journal.pone.0008346

Michael R May, Norman C Ellstrand + Show 4 more

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https://doi.org/10.1371/journal.pone.0008346

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Abstract

BackgroundThe distribution of Palmer's oak (Quercus palmeri Engelm.) includes numerous isolated populations that are presumably relicts of a formerly larger range that has contracted due to spreading aridity following the end of the Pleistocene.Principal FindingsWe investigated a recently discovered disjunct population of Palmer's oak in the Jurupa Mountains of Riverside County, California. Patterns of allozyme polymorphism, morphological homogeneity, widespread fruit abortion, and evidence of fire resprouting all strongly support the hypothesis that the population is a single clone. The size of the clone and estimates of annual growth from multiple populations lead us to conclude that the clone is in excess of 13,000 years old.ConclusionsThe ancient age of the clone implies it originated during the Pleistocene and is a relict of a vanished vegetation community. Range contraction after climate change best explains the modern disjunct distribution of Q. palmeri and perhaps other plants in California.

Highlights

Numerous woody species of plants in the southwestern United States exhibit scattered distributions characterized by small, isolated populations, often occurring in suboptimal habitats [1]
The ancient age of the clone implies it originated during the Pleistocene and is a relict of a vanished vegetation community
We present allozyme data confirming the clonal nature of the stand at Jurupa, as well as indirect estimates of the age of the clone that suggest its persistence since the Pleistocene

Summary

Introduction

Numerous woody species of plants in the southwestern United States exhibit scattered distributions characterized by small, isolated populations, often occurring in suboptimal habitats [1]. One explanation for these scattered distributions is range contraction resulting from spreading aridity and increased temperatures following the end of the last glacial period in the late Pleistocene [2]. One species that demonstrates this scattered distribution is Palmer’s Oak (Quercus palmeri Engelm., = Q. dunnii Kellogg). The distribution of Palmer’s oak (Quercus palmeri Engelm.) includes numerous isolated populations that are presumably relicts of a formerly larger range that has contracted due to spreading aridity following the end of the Pleistocene

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