Gender expression of 145 individually marked Pinus pinea trees planted in the arid transition zone between the Mediterranean district and the Negev Desert in Israel was recorded for thirteen consecutive years (1988 – 2000), from the age of nine to twenty-one. Like several other young Mediterranean conifers, P. pinea trees frequently change their gender expression. On average, each tree expressed 5.2 gender situations during those 13 years. The proportion of all reproducing trees, and monoecious as well as female to male ratio, followed the changes in annual rainfall in the first eight flowering years. Three unusually rainy El Niño years (1988, 1992, 1995), two years that followed a rainy El Niño year, and a regular rainy year, considerably increased the trees' monoeciousness in the population. The young trees began their reproduction as males, and about half of them gradually became monoecious. This trend, which is typical also for P. pinea trees growing in humid habitats, ceased at the age of 17 years, when drought, combined with strong competition over water in a stand that should have undergone two essential thinning treatments that were not done, totally suppressed the female allocation and only some maleness remained. Maleness as a stress response can be used as a tool for forest management, especially when deciding on essential thinning. The above reflects a highly adjustable phenotypic plasticity in resource allocation to reproduction, which seems to be advantageous mainly in both young and physiologically weak small trees on the one hand, and in stressed older ones on the other.
מאת: S. Lev-Yadun
תאריך פרסום: יוני, 2021
מהדורה: 13 (2)
סוג מאמר: מאמר מחקר
קישור להורדה: journal13-2-3.pdf