Restoration success in afforestation sites established at different times in arid lands of Central Anatolia

Abstract

Restoration of degraded lands is among the major challenges in Arid and semi-arid ecosystems. Therefore, in many regions where arid and semi-arid climates prevail, afforestation studies are carried out for restoration purposes. This study evaluated long-term afforestation practices in terms of ecosystem restoration in the arid lands of Central Anatolia, Turkey. For the study, sample afforestation sites of different ages were chosen in the Tuz Gölü-Konya basin. Species in the sites included black pine (Pinus nigra), Russian olive (Elaeagnus angustifolia), sweet almond (Prunus dulcis), black locust (Robinia pseudoacacia), narrow-leaved ash (Fraxinus angustifolia), and mahaleb cherry (Prunus mahalep). For each sampling area, the survival rates, height, and diameter values of species were recorded. Litter on the forest floor was sampled and then representative soil pits were dug at each site to sample soil from different layers (30, 60, 90, and 120-cm deep) of the profile. Bulk density, texture, lime content, pH, salinity, cation exchange capacity (CEC), and carbon (C) and nitrogen (N) concentration were determined for each soil sample. Approximately 2/3 of the black pine seedlings had died in the first 8–10 years of afforestation. The mortality rate in almond and mahaleb seedlings was approximately 20%. After 25–27 years of afforestation, 1/3 and 2/3 of the initial almond and Russian olive seedlings were lost, respectively. The mortality rate for other species was about 80% for the same period. Black pine had reached over 6.5 m, increasing its height by about 11-fold over the last 10–25 years. In the same period, the increase in the height of black locust was 2.8-fold, almond 2.6-fold, and ash 2.5-fold. The least height growth (1.7-fold) for this period was recorded for mahaleb. The amount of litter had increased 3- and 5-fold, at 15–17 years and 25–27 years of plantation age, respectively, compared to its increase in the open control site. After 15 years from planting, soil nitrogen (N) concentration at the first 30-cm depth had increased by about 1/3 compared to the open area. At the same depth, the soil pH value had decreased by 0.15 units after 25–27 years compared to the rest of the profile. These data implied that soil restoration had been initiated at all sites.