Estimates of individual-tree narrow-sense heritability and additive genetic coefficient of variation of seven traits of forest trees were compiled from 67 published papers. Distributions of the values for each trait were characterized and compared by calculating medians and running Kolmogorov–Smirnov and Wilcoxon signed-rank tests. Generalizations are possible about at least some of the traits examined. Heritability of wood specific gravity was almost always above 0.3 (median 0.48). Heritabilities for other traits tended to be low: medians ranged from 0.185 to 0.26, and individual values generally ranged from 0.1 to 0.4. Evidence that heritabilities of form traits tend to be higher than those of growth traits was weak. The analysis of additive genetic coefficients of variation suggested that specific gravity tends to have lower values than other traits (median 5.1%), while height and diameter (medians 8.5 and 8.6%, respectively) had lower values than straightness (median 11.65%). Individual-tree volume showed the highest levels of additive genetic coefficient of variation (median 20.3%). The levels of additive genetic variation and heritabilities suggest that reasonable levels of genetic gain can be achieved by screening relatively low numbers of trees.

No abstract

Cedrela odorata L. (Spanish cedar), an economically important timber species native to the American tropics, is the focus of increasing conservation concern due to high rates of deforestation within its native range. To assess the extent of the genetic diversity within and between populations of this species, samples were obtained from 10 widely dispersed populations within Costa Rica and analysed for random amplified polymorphic DNA (RAPD) variation. Fourteen 10‐mer primers were used to generate 97 polymorphic RAPD bands. Presence/absence data for all bands were subjected to a pairwise genetic distance analysis, according to Jaccard's coefficient, then neighbour‐joining cluster analysis was performed on these distances, as was an analysis of molecular variance (AMOVA), to assess levels of differentiation between populations and regions, and Shannon's Diversity Index was used to quantify levels of diversity within and between populations. Results indicated highly significant genetic differentiation (P < 0.004, AMOVA) between populations originating from the North Pacific and Atlantic/South Pacific regions of Costa Rica, with 35.3% of the total variation attributable to a difference between these areas. Little differentiation was recorded between populations from within the same region (P= 0.757, AMOVA), and 65.1% of the total variance was attributable to variation within populations. Estimated values for within‐population diversity, calculated as Hpop/Hsp by means of Shannon's Diversity Index, were found to vary greatly between primers, but the overall within‐population component of genetic diversity was 0.45. Possible reasons for the high degree of intraspecific genetic variation within this species are discussed and the implications of these results for the conservation and use of its genetic resources are described.

No abstract

Swietenia macrophylla King, a timber species native to tropical America, is threatened by selective logging and deforestation. To quantify genetic diversity within the species and monitor the impact of selective logging, populations were sampled across Mesoamerica, from Mexico to Panama, and analysed for RAPD DNA variation. Ten decamer primers generated 102 polymorphic RAPD bands and pairwise distances were calculated between populations according to Nei, then used to construct a radial neighbour-joining dendrogram and examine intra-and interpopulation variance coecients, by analysis of molecular variation (AMOVA AMOVA). Populations from Mexico clustered closely together in the dendrogram and were distinct from the rest of the populations. Those from Belize also clustered closely together. Populations from Panama, Guatemala, Costa Rica, Nicaragua and Honduras, however, did not cluster closely by country but were more widely scattered throughout the dendrogram. This result was also re¯ected by an autocorrelation analysis of genetic and geographical distance. Genetic diversity estimates indicated that 80% of detected variation was maintained within populations and regression analysis demonstrated that logging signi®cantly decreased population diversity (P 0.034). This study represents one of the most wide-ranging surveys of molecular variation within a tropical tree species to date. It oers practical information for the future conservation of mahogany and highlights some factors that may have in¯uenced the partitioning of genetic diversity in this species across Mesoamerica.