Genetic conservation of Parashorea malaanonan (M. Blanco) Merr. in Mt. Makiling, Laguna, Philippines

April 14, 2006 by

Introduction



In the global market, Philippine dipterocarps are well known by their international trade name, Philippine mahogany. This group of tree species has played an important role as the primary export commodity and dollar earner of the Philippines for a long time. Of these, Parashorea malaanonan belongs to the timber group of Light Red Philippine Mahogany. The volume of log export for this species, however, had dramatically plunged during the last decade (Forestry Statistics, FMB, 1997) because of decline in supply.


P. malaanonan is not only economically-important it is also ecologically significant in that it provides shelter and support to other organisms. It commonly grows together with palms, vines, shrubs and other tree species. It is distributed from the north to the south of the Philippines (Newman et al. 1996). The study of Tsumura et al. (1996) on the phylogeny of dipterocarps indicated that Parashorea is a very close relative of the more common Shorea.


P. malaanonan is now threatened by unabated exploitation endangering not only this species but also the other associated species. Although there have been efforts to reverse the adverse effect of massive destruction of forest ecosystems as a result of excessive forest harvesting, very little attention and studies have been directed on the basic science of conservation of forest species as a whole, and much more so on remaining populations of species like Parashorea.


In Mt. Makiling, Laguna, Philippines, a natural population of P. malaanonan spread from the Makiling Botanic Gardens (200 m asl) to the area beyond the Mudspring with an elevation of about 400-450 m asl. The forest has been declared a forest reserve and the population of P. malaanonan here is probably the only remaining intact population of such species in the country.


Basic information about the genetic diversity, mating system and regeneration of P. malaanonan were determined lately by the authors for use in crafting strategies for conservation and sustainable management of the species. Very recently an analysis of inbreeding coefficient of progenies, maternal and adults of the population in Mt. Makiling and its implications to the conservation of P. malaanonan was undertaken. The monitoring of the growth and survival of regenerants in Mt. Makiling is a continuous activity that provides necessary information for updating the conservation strategy for the population of P. malaanonan in the forest reserve.



Materials and methods



In this study, the results of the population genetic analysis conducted in 2004 on 61 trees of P. malaanonan randomly selected in elevations of 250 – 450 m asl in Mt. Makiling. (Lapitan et al. 2005) were evaluated with the results of a related study on the mating system of P. malaanonan (Lapitan and Hyun 2005), and the regeneration of the species in the study site to identify conservation strategies for the population in this forest. Wright’s FIS was calculated from these data to determine the genetic differences between the samples which can be grouped into two adult populations owing to the different elevation of the area from where they were located. The inbreeding coefficient of the progenies, Fe, of the mating system study was also computed and compared with the parental F value. The formulae used are:


Fe = (1- tm)/ (1+ tm),

tm = multilocus outcrossing estimate,

and

Parental F = 1- (Ho / He) where:

Ho = observed heterozygosity,

He = expected heterozygosity under Hardy-Weinberg equilibrium

The regeneration of P. malaanonan was observed and documented. Natural stands within MFR of P. malaanonan from the Makiling Botanic Gardens (200m asl) to the area beyond the Mudspring with an elevation of about 400-450 m asl were surveyed to gather data on natural regeneration of the species. The growth and survival of 2002 regenerants in the forest reserve was particularly monitored from 2002 to 2005. The regenerants from the recent seed production, July-August 2005, were also monitored for growth and survival. The number of surviving regenerants in the reserve was determined through time and compared with survival of those raised in the nursery.


The most appropriate conservation approach and strategy for the species’ population in the MFR was determined based on the following criteria: genetic diversity of the species, mating system and regeneration characteristic, biophysical characteristics of the forest reserve, socioeconomic and institutional considerations. The latter three criteria were assessed using information from available documents and first hand information of the authors.



Results


P. malaanonan’s outcrossing rate estimate and observed heterozygosity, Ho

Table 1 lists the outcrossing rate estimates and observed heterozygosity of P. malaanonan population in Mt. Makiling. The data show the direct relation of the two values, the higher the outcrossing rate estimates, the higher the heterozygosity values. The average heterozygosity was 0.440±0.08.


Coefficients of inbreeding, F, of adult and filial populations of P. malaanonan

Table 2, on the other hand, shows the inbreeding coefficients, F, of the progenies (filial), maternal/parental and adult trees of the population in Mt. Makiling. The coefficients of inbreeding of filial populations (progenies) were for 13 families of P. malaanonan, the same families sampled for the mating system study of Lapitan and Hyun (2005). The coefficients of inbreeding of the mother trees and the progenies (Fe) were compared following the work of Murawski et al. (1994a), to elucidate the importance of mating system versus other influences (e.g. selection, migration and genetic drift) in determining the adult genotypic frequencies. The F value of the parents was –0.200 indicating an excess of heterozygotes while that of the progenies (pooled) was 0.010, which means there was a very small excess of homozygotes among the progenies.


Growth and survival through time of regenerants of P. malaanonan

P. malaanonan is widespread in Mt. Makiling. Stands surveyed indicate the occurrence of natural regeneration dating back to several decades past. Mature trees, saplings and seedlings were found within 30 m radius of 70-100 cm diameter trees (Figure 1).


The growth and survival of regenerants both in the field (Figure 2) and in the nursery (Figure 3) declined through time with those in the field declining more than those in the nursery. Lapitan and Hyun (2005) had reported a loss of about 80 seedlings/m2 directly under the canopies of mother trees from 90/m2 to 10/m2 after the first year. Gauging from the density of trees in the stands visited, the number of seedlings that usually survive to adulthood is less than 1/m2.

Latest news

Oldest news

Filed Under: Sivilculture
[logo-slider]