Genetic comparison between natural and planted populations of Pinus brutia and Cupressus sempervirens in Syria

Authors: BATOUL N. AL-HAWIJA, VIKTORIA WAGNER, ISABELL HENSEN

Abstract: There is wide consensus that ongoing deforestation contributes to global warming and poses a threat to species diversity. Less understood is whether the practice of creating plantations might also erode genetic diversity and undermine the genetic structure of tree populations. We tested these hypotheses in natural and planted populations of Pinus brutia Ten. subsp. brutia and Cupressus sempervirens L. var. horizontalis (Mill.), 2 important forestry species in the Mediterranean region. We used plant material from 3 different bioclimatic regions in Syria. Using RAPD markers, we evaluated the genetic diversity and structure of 12 populations of P. brutia (6 natural, 6 planted) and 9 populations of C. sempervirens (3 natural, 6 planted). Expected heterozygosity (H_e) and percentage of polymorphic loci (PPL) were high in both species (P. brutia: H_e = 0.241, PPL = 81.2%; C. sempervirens: H_e = 0.241, PPL = 78.8%). In accordance with our assumptions, plantations of P. brutia manifested significant reduction in mean genetic diversity; this result, however, was not revealed in C. sempervirens. Analysis of molecular variance (AMOVA) demonstrated that the genetic structure of plantations differed from that of natural populations. Interestingly, plantations of both species harbored more genetic differentiation among them than natural populations. The partitions created by AMOVA also showed a significant differentiation between 2 groups, natural populations versus plantations in the 2 species, and among bioclimatic regions only in C. sempervirens. This result was corroborated by cluster analyses, which indicated a closer relationship among populations from the same geographic region. Genetic distance was positively related to geographic distance only in natural populations of P. brutia. Plantations in our research showed a significant reduction in genetic diversity, particularly in P. brutia, and stronger among-population genetic differentiation compared to natural populations. We recommend that forest management incorporates genetic diversity and differentiation as an important criterion for selecting appropriate tree stock material.

Keywords: Deforestation, genetic differentiation, genetic diversity, genetic structure, plantations, Syria

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