Geographical variation on cone and seed production of natural Pinus halepensis Mill. forests in Tunisia

Aleppo pine (Pinus halepensis Mill.) is found in discontinuous bands along the Mediterranean Basin, usually at low elevations and in dry climates. This study was conducted to relate bioclimatic zones and geographic distribution with representative individual tree of populations for cone number and weight from the driest to the wettest Aleppo pine forest zones. Epidometric values were recorded in all sample stands in the monitoring plots set in 79 native populations from the Algerian border to the eastern coast of Tunisia, representing a wide range from each region in northern Africa. Simple and multiple regressions were performed on the data. Results showed that the canopy seed bank increased according to elevation, latitudinal and longitudinal gradients. The simple regression analysis showed a latitudinal effect positively relating increasing latitude to greater cone crop. Similarly, longitudinal and elevation variations were related to significant differences in cone dimensions. Higher average seed mass was related to populations located westwards or at higher elevation. The multiple regression analysis indicated that the longitudinal variations were the most determinant geo-positional factors in Aleppo pine cone dimensions and average seed mass in natural Aleppo pine forests in Tunisia.

Research highlights
► In Tunisia, the Aleppo pine forest showed a decreasing tendency in stand characteristics southward.
► This tendency was observed from the wettest zone located in the north to the driest in the south.
► Cone dimensions and seed variables were affected by bioclimatic zones and geographical gradients.
► Cone size and seed number decreased from sub-humid to semiarid with increasing aridity.
► High average seed mass was related to populations located westwards or at higher elevation.