Intraspecific variability and genetic selection of Aleppo pine
In order to explore the geographic variability of Aleppo pine, comparative multi-site plantations were used. In the present study, the emphasis was on exploiting the oldest experiments dating from the 1960s. The initial experimental network implemented by forestry research included 7 devices installed in ecologically contrasting sites. Actually, only four can be exploited, namely: Souiniet (humid), Korbous (sub sub humid), Jbel Abderrahmane (sub sub humid) and Henchir Naame (semi-arid). These trials regroup 40 provenances, including 29 from Tunisia; the other provenances are distributed unevenly between Morocco, Italy and Palestine.
Aleppo pine is one of the dominant forest species in Tunisia, favoured by its great regeneration capacity, plasticity, climatic stress tolerance, and multiple products: wood, edible seeds, vegetable seed oil, essential oils from leaves. For these reasons it has been used massively as for reforestation.
But the wide geographical distribution of the species might imply variation in adaptive and productive traits. The use of genetic material well adapted to the environment and better performing allows for valorization of the resource and offers a guarantee of success for new reforestation. In this context, selection of the best provenances from comparative trials is an interesting research issue.
Growth and quality characters sat the age 29 were analysed, namely: tree height, diameter at 1.30 m, tree shape and the wood density. The results highlighted a high variability between provenances, both at intrastational and interstational level.
For vigor, the behavior of Tunisian provenances differed in two groups, each attached to a well-defined geographical region:
- A continental region located in the West from North (Fernana) to South (Dernaîa), including the best performing provenances.
- A central and coastal region regrouping the worst performing provenances.
Nevertheless, Southern provenances show a better shape than Northern.
The large phenotypic variability on the one hand and the high heritability of the characters studied on the other allow for an elevated genetic gain by selection of provenances.
The average of genetic gains amount to:
• 14% (9-21%, depending on the experimental sites) in height;
• 25% (15-35%) in diameter;
• 7% (5-12%) for form;
• 12% (7-21%) for wood density.
The presence of marked geographic variability between the provenances tested leads, in practice, to the possibilty of making a selection for the benefit of the best performing provenances, a selection combining at the same time good survival, better growth, better shape and better quality of the wood. Therefore, under conditions similar to those of experimental sites, the harvesting of reforestation seeds should, preferably, be oriented towards the following indigenous stands:
Korbous (sub humid) : Selloum, Takrouna, Bérino, M'Guila et Ain Zeres.
Jbel Abderrahmane (sub humid) : Selloum, Ouergha, Bérino, Takrouna et Mellègue.
Souiniet (humid): Dernaïa, Oum Jedour, Semama, Mellègue et M'Guila.
Henchir Naame (semi-arid) : Selloum, Bérino, Mellègue, Dernaïa et Ouergha.
Impacts and weaknesses
Provenance experimental plantations can be exploited for two purposes: ex-situ genetic conservation and selection of provenances. The use of the best performing provenances in reforestation projects is likely to significantly improve the success and the productivity of species in plantation.
Thanks to their importance and their experimental value, the trials deserve to be well maintained and monitored regularly in order to obtain better profit.
Despite the interest of the results obtained, there had been no transfer of results in practice, being this fact sheet a first attempt. Efforts should be made by specialist researchers in collaboration with forest technicians to vulgarize research results concerning the choice of the most suitable provenances for each type of environment.