We investigated the relationship between shoot branching, shoot growth, leaf phenology and seasonal changes during three consecutive seasons in three natural populations of Argania spinosa ((L.) Skeels) in south west Morocco. Rainfall showed two peaks in autumn and winter but summer was dry. Locality, climatic season, genotype (tree/locality) and observation date influence differently all traits. Shoot branching, shoot elongation and leaf emergence were mainly dependant on cumulative rainfall recorded in autumn and winter. When water stress is high, trees were stressed and leaf fall was more intense since 75.4% and 78.9% of leaves were lost in late summer in dry seasons. But after lower or moderate water deficit, leaf drop was less important since only 57.7% of leaves were lost in humid seasons. If dry conditions were spread over a longer period, trees are completely defoliated. Thus, among the 90 trees in the three stations, 45.6% were completely defoliated in autumn in dry season, while only 2.2% were completely defoliated in autumn in humid season. This result suggests that some genotypes are resistant to dry conditions and will be useful for selecting plus trees which are essential for management and conservation practices of genetic resources in argan forest.
Key words: Argania spinosa, defoliation, budburst, shoot growth, leaf drop.
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