Geographic variation in growth, survival, and susceptibility to the processionary moth (Thaumetopoea pityocampa Dennis & Schiff.) of Pinus halepensis Mill. and P. brutia Ten.: results from common gardens in Morocco

Topical collection: Mediterranean Pines

Adaptation of Pinus brutia and Pinus halepensis to harsh Moroccan environments varied considerably among populations, with variation following marked geographic clines.

Context Mediterranean pines are drought tolerant species that play relevant ecological and economic roles in North Africa. Mediterranean pines harbor huge intraspecific variation in adaptive traits.
Aims Exploring the relative performance of different seed sources and analyzing the genotype by environment (G × E) interaction becomes, thus, essential for maximizing the efficiency of any reforestation program.
Methods We present the results of a comprehensive quantitative analysis of growth, survival, and resistance to the processionary moth of 57 populations of P. halepensis Mill. and P. brutia Ten. tested under severe drought conditions in two contrasting Moroccan test sites differing in water regime, soil, and physiographic conditions.
Results The results indicated the existence of considerable variation between species and among populations within species in growth, survival, and susceptibility to the processionary moth (Thaumetopoea pityocampa Dennis & Schiff.), but low plasticity across sites, despite the apparently large environmental differences between them. On average, P. brutia performed better than P. halepensis. The G × E interaction was significant for all traits and ages, but an in-depth analysis revealed that the main source of the interaction was due to large differences in residual variances across sites, while the relative population ranks remained highly consistent across sites.
Conclusion Growth and survival of Aleppo pine populations followed well-defined geographical clines, with populations from the Eastern range of the distribution, particularly those of Greece, showing outstanding performance. The two local Aleppo pine populations were, however, also among the best-growing and surviving populations. Superiority of Eastern Aleppo pine populations was not considered high enough to recommend their use in reforestation programs. Aiming to preserve local genetic resources, local seed sources are preferred for reforestation in the dry areas of Morocco. Planting middle to high elevation Turkish populations of the non-native P. brutia is also an alternative, especially in more mesic sites. The reduced G × E suggests that the above recommendations may be valid, even in the context of future climate change.

Mediterranean pines, Intraspecific genetic variation, Population differentiation, Phenotypic plasticity, Genotype by environment interaction, Drought, Herbivory resistance, Pest resistance, Climate change

Sbay, H. & Zas, R. Annals of Forest Science (2018) 75: 69.

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Data availability
The phenotypic data have been deposited in DIGITAL.CSIC repository:; DOI (Sbay and Zas 2018).

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