RIYADH: As the Saudi Green Initiative moves from setting targets to delivering results, a central challenge remains: How can the Kingdom grow more than 600 million trees by 2030 without placing further pressure on its scarce water resources? More than 159 million trees had been planted and 1 million hectares of degraded land restored by early 2026, the Ministry of Environment, Water and Agriculture announced in March. Thomas Crowther, professor of environmental science and engineering at KAUST, told Arab News that the target is achievable, but success will depend on more than planting trees. “That scale of regeneration is undoubtedly possible, but the key to success will not only be the ‘planting’ of trees,” he said. Regeneration, he explained, involves removing the pressures that prevent nature from recovering, allowing trees and other vegetation to return naturally. In parts of the Kingdom where severe drought and overgrazing have been addressed, ecosystems have demonstrated considerable potential for recovery. Saudi Arabia aims to plant more than 600 million trees by 2030, as part of its wider goal of 10 billion trees. More than 159 million trees had been planted and 1 million hectares of degraded land restored by early 2026. Native species, treated wastewater and rainwater harvesting are central to making large-scale planting sustainable. Alexandre Rosado, professor of bioscience, environmental science and engineering at KAUST, shared that assessment. “Yes, I think it is achievable,” he told Arab News. While describing the target as ambitious, Rosado said the Kingdom’s diverse landscapes offer opportunities for different restoration approaches. Success, he stressed, depends on matching native species to suitable locations and available water resources. He said the program’s use of native species, rainwater and treated wastewater, alongside efficient irrigation and natural regeneration, provides a sound foundation. Rosado also emphasized the importance of soil health and the microorganisms that help plants grow and withstand environmental stress. Identifying successful restoration sites, learning from them and maintaining long-term care will be essential to ensuring lasting ecological benefits. The 600 million-tree target is an interim milestone toward the 10 billion trees announced when SGI was launched in March 2021. The initiative’s 2023 roadmap outlined the scale of the challenge, noting that Saudi Arabia's rainfall, arable land and forest area are all below global averages. The area of restored land has expanded from 18,000 hectares at the initiative’s launch to 250,000 hectares in 2024 and 1 million hectares by early 2026, according to Minister of Environment, Water and Agriculture Abdulrahman Al-Fadhli. The 2030 target is 2.5 million hectares. “This achievement proves that land restoration is possible even in the most challenging environments,” Yasmine Fouad, executive secretary of the UN Convention to Combat Desertification, said in the ministry's statement. The first months Crowther identified drought and overgrazing as the main obstacles to tree growth in the Kingdom. “If young saplings can grow in areas where they have access to some natural moisture — like wadis (valleys) and river beds — then they can grow well,” he said. Allowing vegetation to recover also requires keeping grazing pressure at sustainable levels, he added, giving young plants the opportunity to establish themselves and eventually provide shade for other vegetation. “The first months are critical because the roots are still developing,” Rosado said. Even drought-tolerant native species need support during their establishment, he explained. Healthy nursery-grown saplings, planting during cooler months, targeted watering and protection from grazing animals can significantly improve survival rates. Rosado’s team is studying microorganisms adapted to extreme environments to determine whether they can help species such as Sidr establish roots and withstand environmental stress. The research aims to establish whether these microbial partnerships can improve survival and potentially reduce irrigation requirements over time, although their effectiveness must be demonstrated through field trials. The water question “A program on this scale will need water, especially during establishment, but careful planning can substantially limit pressure on freshwater resources,” Rosado said. He described the initiative’s emphasis on water reuse and efficient irrigation as essential. Treated wastewater can provide a valuable supply where quality and delivery systems are suitable, while rainwater harvesting and irrigation adjusted to soil moisture levels can help maximize available resources. The ministry has also highlighted rainfall as an important resource. In its March statement, Al-Fadhli said projects using dam water and harvesting rainwater were helping advance the 2030 land restoration target. Vice Minister of Environment, Water and Agriculture Mansour Al-Mushaiti said the National Cloud Seeding Program had increased rainfall and contributed to a 50 percent reduction in dust storms in 2025 compared with the previous year. Rosado said monitoring water consumption as trees mature, particularly during dry years, would be equally important. Tracking soil salinity alongside water requirements would allow restoration teams to adjust irrigation before conditions deteriorate, protecting vegetation while conserving water. Crowther also pointed to the wider environmental benefits of successful regeneration. Sustainable vegetation growth can lower surrounding temperatures and improve water retention, he said, with local agriculture among the sectors that stand to benefit most from these effects. The mangrove advantage “Mangroves are absolutely vital ecosystems, providing habitat for thousands of fish and invertebrate species, and also protecting the land from extreme events,” Crowther said. Restoring mangroves across suitable natural habitats could strengthen fisheries and support communities whose livelihoods depend on coastal ecosystems, he added. Rosado said mangroves were an important component of the initiative because they deliver multiple environmental benefits, including carbon storage, coastal protection and nursery habitats for young marine species. “They also have a particular advantage in a water-scarce country: In suitable coastal locations, seawater and natural tidal exchange support their growth without the freshwater irrigation inland planting may require,” he said. His team also studies the microorganisms beneath mangrove forests, which help recycle nutrients and influence plant health and carbon cycling in coastal sediments. Understanding these processes, he said, can improve restoration strategies. Mangrove restoration is most effective when natural tidal flows are maintained, sediment conditions are suitable and young seedlings are protected, Rosado explained. Combining new planting with the conservation of existing forests can extend these benefits along the coastline. Beyond the count For Crowther, the number of trees planted is not, on its own, a sufficient measure of success. “Successful regeneration is when ecosystems are returning to their own momentum,” he said. Rosado said planting figures indicate the scale of activity, but survival rates and the benefits trees deliver to ecosystems provide a more meaningful assessment of progress. “For me, success is healthy vegetation that supports biodiversity and naturally regenerates,” he said. Crowther said planting can help initiate ecological recovery in some areas. In others, vegetation can return naturally once the environmental pressures preventing its growth have been removed.