Pedoclimatic and Landscape Conditions of Tunisian Olive Groves

Tunisia is simultaneously a Mediterranean and a Saharan country, with soils reflecting such climatic, morphological, and geological diversity. According to the French system of soil classification, the soils of Tunisia are classified as podzols, vertisoils, red Mediterranean soils, calcic-magnesic soils (dominant soils), brown and isohumic soils, and saline and hydromorphic soils, along with poorly evolved soils in the most arid regions. The climate is characterized by a soft winter and a hot summer. Precipitations are irregular and present a gradient between north and south with the highest precipitation in the northwest (1500 mm/year). The center of the country is characterized by a semiarid climate, and mean annual precipitation is moderate (200–400 mm) and occurs between October and May. The southern climate is dry (60 mm/year). Olive tree crops include deep brown or alluvial soils with a well-balanced tex ture. These soils are found across various bioclimatic areas. Olive trees extend over 1.8 million ha. Clay soils are placed mainly in the north where bioclimatic areas range between humid and semiarid. In semiarid regions, soils are poor in organic matter (less than 1%), rich in calcium carbonate, with alkaline pH (>7.8), and moderately calcareous (>15%). Also, the cation exchange capacity is low, and the nutrient circulation and penetration are limited. Tunisian soils are subjected to severe climatic conditions, including drought (regularly affecting over 3/4 of the surface of the country), short duration torrential rainfall, and increasingly impactful anthropogenic factors along the coast. All these factors turn the soils fragile and increase their sensitivity to their degradation, either mechanical or chemical. Olive tree crop lands were traditionally protected from runoff through hydraulic infrastructures (terraces, tabias, Meskat system, and Jessours), benefiting from additional water along the rainy periods in the central and southern regions. All the above conditions allowed for olive trees to be planted in marginal zones characterized by alternating production. The challenge currently is to adopt novel strategies such as agroforestry based on cropping and green manures, in order to improve soil structure and enhance soil fertility rates as basis for enhancing the sustainability of olive grove landscapes.