SUMMARYMonoterpene and isozyme loci, used as markers to study the genetic structure of Scots pine {Pinus sylvestris L.) native to Scotland, showed that the endemic populations are not genetically impoverished, in spite of severe contraction in range and numbers as a result of both natural and anthropogenic causes. On the contrary, variability in the relict populations is almost the highest of any plant species studied, with average heterozygosities of 0-33 for monoterpenes (five loci) and 0-30 for isozymes (16 loci). The overwhelming proportion of this variability (> 95 "") was within populations, even though significant differences in gene frequencies of many individual loci existed among populations. Multiple-locus comparison of gene frequencies among populations, resolved by canonical variate analysis, showed no coherent geographic pattern of differences from population to population or region to region, with one major exception: certain populations in northwestern Scotland (Wester Ross) were distinct from all others and each other. The pattern of variability of the biochemical markers was consistent with that of metrical and physiological traits reported in the literature. These traits, in turn, show relatively little genetic affinity between eonteniporary Scottish and continetital European populations. The genetic evidence, together with the anomalous distribution of pine pollen in the British Isles during the Holocene, suggests that the Caledonian race of Scots pine originated endemically from more tban one refugium after the last glaciation.

We have used polymorphic chloroplast simple-sequence repeats to analyse levels of genetic variation within and between seven native Scottish and eight mainland European populations of Scots pine (Pinus sylvestris L.). Diversity levels for the Scottish populations based on haplotype frequency were far in excess of those previously obtained using monoterpenes and isozymes and con¢rmed lower levels of genetic variation within the derelict population at Glen Falloch. The diversity levels were higher than those reported in similar studies in other Pinus species. An analysis of molecular variance (AMOVA) showed that small (3.24^8.81%) but signi¢cant (p40.001) portions of the variation existed between the populations and that there was no signi¢cant di¡erence between the Scottish and the mainland European populations. Evidence of population substructure was found in the Rannoch population, which exhibited two subgroups. Finally, one of the loci studied exhibited an allele distribution uncharacteristic of the stepwise mutation model of evolution of simple-sequence repeats, and sequencing of the PCR products revealed that this was due to a duplication rather than slippage in the repeat region. An examination of the distribution of this mutation suggests that it may have occurred fairly recently in the Wester Ross region or that it may be evidence of a refugial population.

Variation in the non-coding region of chloroplast DNA (cpDNA) was studied to determine the route and pattern of postglacial recolonisation of native oak throughout mainland Britain. In total, 1076 mature oak trees of either Quercus petraea (Matt.) Liebl. or Quercus robur L. from 224 British ancient woodland sites were analysed, and represent the largest and most saturating molecular analysis of British oak undertaken to date. The majority of oaks (98%) possessed one of the three cpDNA haplotypes from lineage B that are commonly found in Spain and western regions of France. Thus, our findings strongly support the hypothesis that most native British Q. robur and Q. petraea originate from a Pleistocene refugium in the Iberian Peninsula. A haplotype previously thought to be the result of a de novo postglacial mutation in East Anglia, Native and Nonnative in British Forestry. Proceedings of a Discussion Meeting, March 31-April 2, 1995. University of Warwick, pp. 38-55] was found at several sites in eastern Britain, including major population clusters in East Anglia, Tyneside and northeast Scotland. We propose that this haplotype was introduced to Britain via normal postglacial colonisation processes. Less than 2% of oak trees sampled possessed haplotypes from lineages which originate from more eastern refugia (Italy and Balkans). Whilst human-mediated translocation may be responsible for the occurrence of these haplotypes in Britain, single long distance dispersal events (of between 300 and 500 km from France) cannot be excluded for at least one case. The majority of populations sampled (including those where both species are present) were fixed for a single haplotype (69%). However, significant areas of mixed haplotype woods occurred in the Welsh Marches and Scotland and the proportion of population fixation was lower and intra-population diversity higher for Q. robur (G ST ¼ 0:661; h S ¼ 0:224) than for Q. petraea (G ST ¼ 0:884; h S ¼ 0:089). The distribution of cpDNA variation in British oak populations is discussed and interpreted in the light of hypothesised recolonisation routes and dynamics, inter-specific hybridisation and chloroplast capture, and human impacts due to the management of ancient woodland. #

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