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A morphological and volatile terpene analysis of Pinus balfouriana to test for the mountain island effect in the Klamath Mountains
Pinus balfouriana Grev. and Balf., foxtail pine, is endemic to California, occurring as two subspecies: P. balfouriana ssp. austrina in the southern High Sierra and P. balfouriana ssp. balfouriana 500 km to the north in the Klamath Mountains. Previous research has shown that the northern subspecies is characterized by higher genetic diversity than the southern subspecies. This higher genetic diversity has been attributed to the mountain island effect (MIE), whereby reproductively isolated stands that are restricted to mountain peaks evolve independently via natural selection and/or genetic drift. To date, research on morphological and terpene chemistry variation in foxtail pine has been limited to analyses distinguishing the two subspecies. No work has examined the variation among stands for these traits in the northern part of the range. Here I test if there is phenotypic evidence of the mountain island effect. Twenty anatomical, morphological, and chemical characters were sampled from twenty stands across the range of the species in the Klamath Mountains. Stands were grouped into seven regions according to which mountain they grew on. I used multivariate analysis of variance (MANOVA) to test if there were differences among stands and regions. If there were differences, I used canonical discriminant analysis (CDA) to reveal which traits contributed to the differentiation. I used cluster analysis and the Mantel test to investigate whether differences in trait expression were correlated with soil substrate and geographical distance among stands, respectively. Lastly, I used discriminant analysis to see how well trees could be classified into regions and stands within regions. Since the mountain island effect likely operates at fine scales, I expect stronger differentiation within regions than among regions. Moreover, I predicted that the set of traits that discriminates stands within each region will differ across regions. Fifty percent or more of overall variation resided among stands for most of the individual traits, and differences among means were typically quite modest. Nevertheless, I found significant multivariate differences in phenotypic traits among and within regions. As predicted for the MIE, differentiation was more pronounced within regions than among regions. Differences among stands were not correlated with physical distances and different characters discriminated stands within each region. Stands that grew in serpentine soil could not be distinguished from those not growing in serpentine, suggesting that serpentine was not a driving factor for differentiation among stands. Together with previous genetic research, my findings provide support that the MIE is generating distinct mountaintop stands in the Klamath Region.