In situ and Ex situ Conservation of Commercial Tropical Trees - ITTO

210Effects of disturbance and small population sizeDisturbance to natural populations, such as selective logging of dipterocarpspecies and ulin in Central Kalimantan, does not immediately reduce geneticdiversity of the species investigated. It does, however, reduce the outcrossingrates, which means that inbreeding will increase. Population sub-structuringwas also enhanced, as it was found that logged-over populations had differentiatedfrom original populations.Small population size, formed due to fragmentation, was characteristicof the mangrove species populations on the north coast of Jawa island, and ofthe isolated population of P. merkusii at Kerinci National Park. In those smallpopulations of mangrove species, reduced genetic diversity was observed. Asan extreme case, in the isolated population of P. merkusii, no variability wasdetected on any of the isozyme loci investigated, indicating that homozygosityhas been fixed. Another important finding from the P. merkusii study was theexistence of mating preferences between genotypes in a seed orchard. Morespecifically, trees with high outcrossing rates preferred male gametes of lowfrequencies or very rare alleles. This phenomenon could lead to changes inallelic proportions in subsequent generations.Implications for conservation programsConsidering the fact that almost all species studied are outcrossers, in situconservation programs for most tropical species should be directed atmaintaining high genetic diversity by allowing gene flow to take place amonglocal or sub-populations. This means that severely disturbed forests should berestored to form a panmictic population. Gene flow would encounter inbreedingand/or genetic drift. To avoid negative effects of fragmentation, in forestryoperations it is advisable to leave several mature individual trees, which willserve as “stepping stones” between local populations.The results of population genetic studies will help to design samplingstrategies for ex situ conservation programs. Sub-structuring of populationsand different levels of inbreeding will affect sampling processes, becausesampling depends on the amount of genetic diversity in each populations and onthe extent of genetic divergence between them. Detection of assortative matinghas the consequence that as many as possible alleles should be collected.The provenance concept provides a link between in situ and ex situconservation of forest tree genetic resources. Sampling should recognizeprovenances as units of genetic resources. As shown by a study in plantationsof Paraserianthes falcataria, any plantations that are established from