Seed source variation : assessment of potential for improving plantation forestry in Rwanda

Mugunga, Canisius P. (2002-04)

Thesis (MScFor)--Stellenbosch University, 2002.

Thesis

ENGLISH ABSTRACT: Nine species in ten different seed source trials were evaluated with the aim of understanding their potential as exotics in improving plantation forestry in Rwanda. Assessment was based on tree growth and stem quality, juvenile-mature and trait-trait phenotypic correlations as well as the relationship of seed source performance and the locational variables of seed origin. Eucalyptus saligna, E. urophylla, Pinus maximinoi and P. tecunumanii proved to be very promising as plantation species and are highly recommended. P. patuia and Grevillea robusta are also recommended for plantation and agroforestry purposes respectively. P. caribaea and P. kesiya proved to be very poorly adapted under local conditions and should be retested if resources were available. All trials except E. urophylla, and P. maximinoi (the two had very few degrees of freedom) showed significant differences of varying degrees in different traits between seed sources indicating their potential for genetic improvement through selection and breeding. Similarly, all trials except E. urophylla, and P. maximinoi indicated significant juvenile-mature phenotypic correlations of varying degrees in different traits, with height showing strongest relationships. On average, trait-trait relationship was observed to be strongest between diameter and volume, followed by height and volume, height and branching pattern, stem form and branching pattern, stem form and height, branching pattern and volume, and diameter (and volume) and stem form in that order. Based on juvenile-mature phenotypic correlations, tree height at 15 and 16 years can be predicted as early as at three years for E. tereticornis (r :::0;.4680) and P. kesiya (r:::;0.5530) respectively, while that at 14 and 16 years in P. tecunumanii (r:::;0.4820) and P. patuia (r:::;0.5562) can be predicted using height at four years. This however may only be true where genetic and phenotypic relations are strong (as may be the case in E. tereticornis since high heritability estimates were obtained). The following additional recommendations are made under this study: To study the effect of growth rate on wood properties of very fast growing pine species; to introduce other tropical species such as E. deglupta and P. oocarpa so as to diversify species; carry out studies to better understand the effect of altitude on the adaptability of the exotic tree species in the tropical and sub tropical environments and lastly, carry out genetic tests in future so as to ascertain the obtained results on age-age and trait-trait correlations in this study.

AFRIKAANSE OPSOMMING: Nege spesies in tien verskillende saadbronproewe is geëvalueer met die doeI om hulle potensiaal as eksotiese spesies te verstaan sodat plantasie-bosbou in Rwanda verbeter kan word. Die evaluering is gebaseer op boomgroei en stamkwaliteit, jongeling-volwasse en eienskap-eienskap fenotipiese korrelasies, sowel as die verhouding tussen saadbronprestasie en die omgewingveranderlikes van saadoorsprong. Eucalyptus saligna, E. urophylla, Pinus maximinoi en P. tecunumanii blyk baie belowend te wees as plantasiespesies en word sterk aanbeveel. P. patuia en Grevillea robusta word ook aanbeveel vir die doeleindes van plantasie- en agrobosbou onderskeidelik. P. caribaea en P. kesiya blyk baie swak aangepas te wees onder plaaslike omstandighede en moes weer getoets te word, sou die hulpmiddele beskikbaar wees. Alle proewe (behalwe E. urophylla en P. maximinoi - dié twee het baie min vryheidsgrade gehad) het beduidende verskille van afwisselende grade getoon tussen saadbronne in verskillende eienskappe. Dit dui aan dat hulle potensiaal het vir genetiese verbetering deur seleksie en teling. Eweneens het alle proewe behalwe E. urophylla en P. maximinoi beduidende jongeling-volwasse fenotipiese korrelasies van afwisselende grade in verskillende eienskappe getoon, met hoogte wat die sterkste verhoudings getoon het. Oor die algemeen was die eienskap-eienskap verhouding die sterkste tussen deursnee en volume, gevolg deur hoogte en volume, hoogte en vertakkingspatroon, stamvorm en vertakkingspatroon, stamvorm en hoogte, vertakkingspatroon en volume, en deursnee Cen volume) en stamvorm, in daardie volgorde. Op grond van jongelingvolwasse fenotipiese korrelasies kan boomhoogte op 15 en 16 jaar op so vroeg as drie jaar voorspel word vir E. tereticornis Cr 0 0.4680) en P. kesiya Cr 0 0.5530) onderskeidelik, terwyl boomhoogte vir P. tecunumanii Cr 00.4820) en P. patuia Cr 0 0.5562) op 14 en 16 jaar voorspel kan word op vier jaar. Dit kan egter net juis wees waar genetiese en fenotipiese verhoudings sterk is (soos die geval kan wees met E. teretiornis, aangesien hoë erflikheidskattings verkry is). Die volgende addisionele aanbevelings word in hierdie studie gemaak: om die effek te bestudeer van die groeitempo op die houteienskappe van denspesies wat baie vinnig groei, te bestudeer; om ander tropiese spesies soos E. deglupta en P. oocarpa ook te betrek ten einde die spesies te diversifiseer; om studies uit te voer ten einde die effek van hoogte op die aanpasbaarheid van die eksotiese boomspesies in die tropiese en subtropiese omgewing beter te verstaan; en laastens, om in die toekoms genetiese toetse uit te voer ten einde die resultate wat in hierdie studie op ouderdom-ouderdom en eienskap-eienskap korrelasies verkry is, te bevestig.

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