Assessing genetic diversity and structure of fragmented populations of eastern white pine(Pinus strobus)and western white pine(P.monticola)for conservation management

Aims Many pine populations in Canada have fragmented distributions resulting from the effects of glaciations,overharvesting and white pine blister rust infections.Forest fragmentation can modify gene flow and reduce genetic diversity.Selective logging can reduce the density of trees,thereby altering mating patterns and increasing inbreeding.The hypothesis of the present study is that forest fragmentation will not increase inbreeding and will have no effect on genetic diversity parameters in the Canadian Pinus moniticola and P.strobus populations targeted because of(i)the long life span of the pine species,(ii)outbreeding and self-incompatibility of P.monticola and P.strobus and(iii)wind pollination resulting in high gene flow among populations.We studied the genetic diversity of P.strobus across its range in Canada,and we completed a detailed analysis of the genetic structure of P.monticola populations from western Canada using microsatellites genetic markers.Methods Seed samples from 10 P.monticola populations and 10 P.strobus populations were collected from western and eastern Canada,respectively.The mother trees included in seed lots were representative of each stand.Genomic DNA extracted from each sample was amplified with microsatellite primers.The intra-and interpopulation genetic diversity parameters were assessed using Popgene and Genepop softwares and the genetic distances among populations within each species using the PowerMarker software.

Behavior of Meiotic Chromosomes in Pinus wallichiana,P.strobus and Their Hybrid and nrDNA Localization in Pollen Mother Cells of the Hybrid by Using FISH

The complete process of meiosis was investigated in Pinus wallichiana, P. strobus and their artificial hybrid （F1） using microsporocytes. It is revealed that there were slightly lower chiasma frequency, lower ring bivalent frequency, lower meiotic index and distinctly higher frequency of aberrance （chromosomal bridges, fragments or micronuclei） in pollen mother cells （PMCs） of the hybrid （F1） than those of the parental species, which showed a certain degree of differentiation between homologous chromosomes of the two parents. However, relatively higher frequency of ring bivalents and higher meiotic index in all the three entities indicate the great stability of genomes of parental species, and the differentiation of genomes between the two parents must have been slight. Total nineteen signal loci of 18S rDNA were observed in nine bivalents of the hybrid （F1）, among which one bivalent bears two loci, while the others have only one. It is suggested that distinct differentiation at genetic level existed in homologous chromosomes of the two parental species, whereas only slight differentiation at karyotypic and genomic levels take place between the parent species.

Regeneration patterns of key pine species in a mixed-pine forest indicate a positive effect of variable retention harvesting and an increase in recruitment with time

Background:Many fire-dependent forests have experienced significant declines in species,structural,and functional diversity.These changes are attributed in part to traditional management approaches that were dominated by even-aged regeneration methods such as clearcutting.Variable retention harvesting(VRH)is an ecologically based forestry practice that involves retention of some mature overstory trees and other biological structures in the postharvest stand to emulate the effects of natural disturbance events.In this study,we examined the effect of a VRH treatment on recruitment of historically dominant pine species and understory vegetation twoand six years after its implementation in a naturally regenerated mixed pine forest in the Upper Peninsula of Michigan,USA.Results:We found greater regeneration of red pine(Pinus resinosa L.)and eastern white pine(Pinus strobus L.)in VRH stands compared to the unharvested controls.Although red pine recruitment was very low during the first 2 years,both species increased significantly from year two to year six.Recruitment responses for the two species did not differ significantly between the aggregated and dispersed retention treatments.We also found high recruitment of deciduous tree species,consisting primarily of sprouts,and red pine exhibited a negative correlation with these sprouts.Treatment,time,and the interaction of treatment and time were significant factors in red pine recruitment.Time had a strong effect on the understory vegetation,with significant decreases in shrubs and ferns over time.Conclusions:The results suggest that VRH enhanced recruitment of red pine and eastern white pine and that this recruitment increased with time.We identify competition from sprouts and unfavorable seedbed conditions as the main factors that limited recruitment of red pine during the first 2 years.To reduce competing vegetation and improve seedbed conditions,we suggest following the VRH with a prescribed fire,mechanically removing sprouts,and implementing herbicide treatments.At a time when changes in global climate exacerbates the effects of traditional drivers of forest degradation,and with the need to maintain biodiversity,new ecologically based forest practices such VRH have the potential to facilitate regeneration of native trees and enhance the resilience of many fire-dependent forests.