Influence de la structure du peuplement et de la sylviculture sur la production de cônes et de graines en plantation forestière de Pinus pinea dans le nord de la Tunisie

Pinus pinea L. is one of the most valuable species used in the Tunisian reforestation program for its ecological, aesthetic and economic value. It was successfully introduced at the beginning of the 20th century along the Mediterranean coast line. Today in Tunisia it occupies an area of 21,000 ha. Despite this importance, little is known, at least in Tunisia, about fruiting, cone yield, variations in\nseed morphology and quality of Pinus pinea and how these different processes are affected by the stand structure and silvicultural practices. It was reported that some factors such as high crop year, overgrazing and illegal harvesting influence seed production. Variation in cone size, seed number per cone, seed viability, seed quality and seed germination behaviour relative to stand conditions (age, diameter at breast height, height, crown diameter, stand\ndensity, social status of tree) were analyzed for three Pinus pinea stands in Mekna III, located in north coastal dunes in Tunisia. The cones were collected in winter 2011 on sample of 10% of trees in DBH classes, counted and weighted.\nThree cones with different sizes (small, medium and large) for each sampled tree were taken and brought to the laboratory. The length and the width (at the widest point) of the cones were measured with vernier callipers, the weight was also determined. Afterwards, seeds were released by heating the cones at 60 °C for 30 mn to 1 hour to open them. Number, size and total weight of seeds per cone were determined. Damaged or not well-developed seeds were recorded, and their viability relative to germination was tested. We will provide sources of variability in cone and seed production relative to stand density, age, social status of trees and silvicultural operations. However the data show that seed production has been low to extremely low, whatever the considered stand. Problems could arise from this deficiency in the future, not only for nut market but also for stand regeneration and species conservation on a long term scale. Therefore proper management and regulation of livestock grazing and cone collection in the Pinus pinea forests is mandatory to both sustainable nut and forest productions.