Dendroecological study of Pinus halepensis and Pinus pinea in northeast coastal dunes in Tunisia according to distance from the shoreline and dieback intensity

Growth decline is a widespread phenomenon on sandy coasts throughout the Mediterranean region. In the northeastern pine coastal woodland of Tunisia, Pinus pinea and Pinus halepensis stands originally afforested to stabilize sand dunes are often damaged. Our objective was to estimate the effect of distance from the shoreline on ring- width variation of two pine species, Pinus pinea and Pinus halepensis located in the Remel and Menzel Belgacem coastal forest land. 15 to 30 trees of each species were selected based on three dieback levels (low, moderate and severe canopy damage). The results of dendroecological analysis show a significant reduction in the mean growth of trees growing near the shoreline for both species. Most stands show a positive correlation with precipitation between October of the previous year to April of the current year. The number of months, when precipitation is correlated positively with growth, is always lower for trees growing near the shoreline than for trees growing in distant stands. However, when the maximum temperature is correlated negatively with growth, the number of months is always higher for trees growing near the shoreline (2 months) than for trees those in distant stands (1 month). Moreover, there was an increased number of missing rings in the 1980s but only in those trees growing near the shoreline and their frequency was only statistically significant for Pinus pinea in the two forest sites. The severity of canopy damage due to being close to the shoreline negatively influenced the growth of both species and could threaten their survival in these areas.