Seeking environmental sustainability in dryland forestry

Forestry systems, including afforestation and reforestation land uses, are prevalent in drylands and aimed at restoring degraded lands and halting desertification. However, an increasing amount of literature has alerted potentially adverse ecological and environmental impacts of this land use, risking a wide range of ecosystem functions and services. The objective of this paper is to demonstrate the potentially adverse implications of dryland forestry and highlight the caution needed when planning and establishing such systems. Wherever relevant, establishment of low-impact runoff harvesting systems is favored over high-impact ones, which might cause extensive land degradation of their surroundings. Specifically, both in hillslopes and channels, scraping, removal, or disturbance of topsoil for the construction of runoff harvesting systems should be minimized to prevent the decrease in soil hydraulic conductivity and increase in water overland flow and soil erosion. In order to negate suppression of understory vegetation and sustain plant species richness and diversity, low-density savanization by non-allelopathic tree species is preferred over high-density forestry systems by allelopathic species. Wherever possible, it is preferable to plant native tree species rather than introduced or exotic species, in order to prevent genetic pollution and species invasion. Mixed-species forestry systems should be favored over single-species plantations, as they are less susceptible to infestation by pests and diseases. In addition, drought-tolerant, fire-resistant, and less flammable tree species should be preferred over drought-prone, fire-susceptible, and more flammable species.