# The Role of Trees in Sand Dune Rehabilitation: Insights from Global Experiences
## 1 Introduction  
Afforestation of arid sandy regions has long been employed as a strategy to combat sand encroachment threatening agricultural and inhabited areas. The establishment ofvegetation on dunes mitigates sand movement, promotes the deposition of fine particles, and enhances soil fertility through organic litter decomposition. Additionally, it improves soil structure and water retention capacity, thereby contributing to ecosystem stabilization. Sustainable forest management in these environments not only supports timber and fodder production but also serves as an important tool in the fight against desertification [1]. Dune ecosystems are inherently dynamic and harsh, shaped by factors such as high solar radiation, persistent winds, proximity to marine influences, and episodic disturbances like drought and sand burial [2]. Plant species that colonize dunes typically exhibit early successional traits, including rapid establishment and wide dispersal, but tend to be poorly adapted to shade and intense competition [3]. This ecological profile renders dune vegetation vulnerable to invasion by more competitive species capable of tolerating these environmental constraints. Sand dunes, formed by the influence of wind and climatic extremes, are a dynamic component of arid and semi-arid landscapes from all around the world. Their mobility causes an important threat to infrastructure, agriculture, and livelihood. To combat these influences, as well as desertification processes, afforestation has been introduced in the last century as a suitable strategy. Through afforestation, trees and woody shrubs have anchored shifting sands, increased surface roughness, as well as built microhabitats that improve the overall ecology. These interventions have been proven to mitigate sand movement, as well as improve soil properties, especially fertility, water retention, and organic content, becoming an essential method in the long-term rehabilitation of ecosystems. At a global level, sand dunes cover many regions and areas. If we group them by size, some of the largest sand dunes are found in China (Badain Jaran Dunes), Argentina (Duna Federico Kirbyus), France (Dune du Pilat), Namibia (Dune 7), Oman (Ramlat Jadilah), and Australia (Mount Tempest). If we group them by their spectacular nature, both ecological and geological, we can mention the Star Dune and White Sands (the USA), Athabasca Dunes (Canada), Erg Chebbi (Morocco), and Mui Ne (Vietnam). Besides their size and uniqueness, these dunes are very diverse. Mostly stable dunes are present in the USA and Canada, where high precipitations and evapotranspiration sustain vegetation cover [4; 5]. The deserts in China are impressive in their coverage (over \(\sim\)600,000 km\({}^{2}\)), size (they have some of the world's tallest dunes), and distinctive dune-lake complexes [6]. Another example from China (the Horqin Sandy Land) also showcases the effect of severe anthropogenic desertification, caused by overgrazing and collecting fuelwood [7]. Another example worth mentioning here comes from Australia, where extensive inland dunefields are present, showing how even vegetated arid dunes have low rates of sand transport because of the resilient native flora [8; 9; 10]. The distribution of plant species in dune systems is closely linked to geomorphological features shaped by wind erosion, sand deposition, and dune movement [11; 12]. For instance, interdune depressions often function as \"vegetation islands,\" where psammophytes, steppe species, and limnocryptophyte-meadow plants can coexist [11]. Afforestation is among the most widely applied methods for stabilizing mobile sand dunes [13]. It not only increases plant cover and soil nitrogen content [14; 15] but also contributes to atmospheric carbon sequestration. Vegetation cover has been shown to enhance soil moisture levels [6], enrich soil nutrient content, and facilitate the recovery of plant diversity [16]. Fixation of shifting sand dunes through afforestation represents a critical first step toward ecological restoration.