Genetic Variation in Tropical Tree Species and Plantations: A Review

The global efforts to restore tropical forests and their productive and ecological

functions through plantation forestry largely depend on the available genetic

variation in the tree species used to establish the plantations. However,

there is limited information on the levels and trends of the genetic variation

and variability of different plantation tree species in the tropics. Therefore,

this study reviews several marker-based studies that have investigated genetic

variation. Most of the top economic species like Eucalyptus tereticornis and

Mansonia altissima are attributed to low levels of genetic diversity, while others

like Pinus caribaea and Swietenia macrophylla still exhibit high expected

heterozygosity across different populations. However, the levels of genetic diversity

assessed may depend on the markers used. Microsatellites, i.e., simple

sequence repeats (SSRs), mostly give higher estimates when compared to other

polymerase chain reaction-based markers. Other factors that typically contribute

to the directional pattern of genetic variation in tropical tree species and

populations include their distribution, density, seed dispersal, succession, and

reproduction. Also, anthropogenic impacts like logging and fragmentation have

contributed to the vast genetic base reduction of many tropical species and populations.

Having adequate genetic variation within the plantation populations is

significant in improving their fitness, resilience, fecundity, productivity, and

other ecological functions. It also provides a basis for tree improvement and

breeding in plantation forests. Although clonal forestry is becoming widespread

and considered highly productive, it is attributed to specific economic,

technical, and ecological risks, such as the increased spread of pests and diseases.

Therefore, further discussions and recommendations to maximise genetic

diversity in tropical (clonal) plantations are provided.