Forest ecosystems that have developed over time line the major rivers of Central Asia. The peoples of the region call this distinctive natural heritage tugai. In Uzbekistan’s dry, hot climate, tugai provides a unique natural habitat that sustains a vital ecological balance. Tree roots stabilise riverbanks, trees and shrubs protect the soil, and their shade moderates the summer heat. Birds nest here, and many animals find food and shelter. Dozens of rare animal species, including the Bukhara deer, depend on these habitats. Desert poplars, willows, oleasters and tamarisk scrub maintain a distinctive natural balance between river and desert. In recent decades, however, climate change and extensive human activity have placed these riverside forests among the world’s most threatened ecosystems.
The value of tugai becomes more apparent as its extent shrinks. Historically, along some of Central Asia’s rivers, tugai forests extended two to three kilometres inland from the banks. Today, in many places, they survive only as narrow, disconnected green strips. Areas where trees, shrubs, reedbeds and wet meadows once joined together have broken into small, separate fragments. For every plant and animal, this means less living space, food and shelter.
Scientists at the Academy of Sciences of the Republic of Uzbekistan have completed a long-term programme of comprehensive research into tugai along the Amu Darya, Syr Darya and Zarafshan rivers and the shores of the Aydar–Arnasay lake system. Field observations were combined with analysis of historical records, satellite imagery and tree rings. The research revealed the richness of these riverside ecosystems, which support 632 plant species.
The research showed that the pressures threatening this diversity are closely interconnected. Warming is increasing evaporation, drought is depleting soil moisture, and earlier snowmelt and shrinking mountain glaciers are affecting the water feeding rivers. Where seasonal inundation becomes less frequent, natural regeneration of tugai becomes more difficult. Land conversion, excessive grazing and the regulation of river flows add to these pressures. Climate change compounds existing stresses and narrows the opportunities for recovery.
The life of a riverside tree often begins hundreds of kilometres away, high in the mountains. Snow accumulated during winter and glacier ice supply rivers with water in the warmer months. Warming is reducing winter snow accumulation and bringing earlier snowmelt, changing the distribution of water throughout the year. Shrinking glaciers weaken the supply of water in summer over the longer term. Faster melting may initially increase runoff, but this temporary rise does not mean that mountain ice reserves are recovering. As those reserves decline, the risk of water shortages during the hottest months grows.
Changes in the mountains thus reach tugai far downstream. When trees need more water, the supply from the river and soil falls short. The condition of tugai depends not only on the total volume flowing down the river each year, but also on whether that water reaches riverside habitats during the growing season.
Under natural conditions, the seasonal rise of a river sustains tugai. Water spreads across the low-lying land beside the river — its floodplain — moistening the soil, replenishing groundwater and creating wet sandy and silty surfaces where seeds can germinate. After the water recedes, moisture retained in the soil helps young plants grow. The next generation of tugai trees depends on this natural cycle.
When inundation becomes shorter, shifts in timing or no longer reaches particular sites, that connection is disrupted. Mature trees may still carry green canopies, but fewer young plants are available to replace them. A seedling whose roots have not yet reached deeper soil dies during its first dry, hot summer. Water flowing in the channel therefore does not mean that all neighbouring tugai receives enough moisture.
Rising temperatures intensify the problem. Long-term analysis for the Zarafshan valley shows warming and declining summer relative humidity. Rainfall in winter or spring does not always compensate for summer water shortages. In hot weather, soils dry faster and plants must replace lost moisture through their roots. When water is scarce, growth slows, trees weaken and surviving dry years becomes more difficult.
Sensitivity to climate was also evident along the Aydar–Arnasay shores. At the study sites, increases in spring rainfall relative to the previous year were associated with a tendency towards greener vegetation in summer; hotter summers showed the opposite relationship. The conclusion drawn from the research is that proximity to a large lake alone does not protect vegetation from heat and inadequate soil moisture.
Salinity compounds moisture shortages, placing tugai under even greater stress. Where water is not sufficiently renewed and salts are not flushed out, strong evaporation increases salt accumulation in the soil. Plants then find it harder to take up water even when some moisture remains. Trees experience water shortage and the effects of salinity at the same time.
Research in the lower Amu Darya and its delta revealed what this transformation looks like. In some areas, desert poplar stands are thinning and moisture-demanding plants are declining, while shrubs and herbs tolerant of drought and salinity are becoming more prominent. As woodland gives way to areas dominated by shrubs and salt-tolerant herbs, the shade, conditions for moisture retention and wildlife habitats also change. Unfortunately, the presence of vegetation where a forest once stood does not mean that the forest itself has survived.
This distinction also matters in Zarafshan tugai. Grasses and other herbs may spread, making a site look green even while its trees are weakened or dying. Greenness alone is therefore insufficient to assess the condition of tugai. The key criterion is whether healthy trees, natural regeneration and species characteristic of the habitat are being maintained.
The findings from three tugai stands along the Syr Darya in the Fergana Valley illustrate the scale of loss. Their combined area fell from approximately 754 hectares in 1975 to 377 hectares in 2025. Over half a century, these Syr Darya tugai stands lost almost half their area. Warming and drought are making the survival and recovery of the remaining fragments even more difficult.
In their research on tugai along the Amu Darya, Syr Darya and Zarafshan, Academy of Sciences scientists found that tree-ring width in the Amu Darya basin declined from 6.96 millimetres in 1949 to 2.46 millimetres in 2022. In the Syr Darya basin, it fell from 11.26 to 1.95 millimetres between 1965 and 2022. Radial growth declined by 65% relative to its historical maximum in the Amu Darya basin, by 83% in the Syr Darya basin, and by nearly 49% during the recent phase in the Zarafshan basin. The sharp decline in radial growth observed in tugai is not an ordinary climatic fluctuation, but a biological signal that ecosystem stability is being disrupted.
The research showed that fragmentation makes tugai increasingly vulnerable. Animals find it harder to move between isolated patches of woodland, while plants have fewer opportunities to spread. Nearby healthy tugai and seed sources are important when a damaged patch needs to recover after fire or prolonged drought. Where trees disappear and the soil becomes exposed, sunlight and wind have a greater effect, encouraging further moisture loss.
Accumulated dry grasses, reeds and branches also increase fire danger. Hot, dry weather creates favourable conditions for fires to start and spread, while dryness and heat can contribute to ignition. Recovery after a fire requires water too. Where moisture is scarce, damaged woodland takes longer to recover or is replaced by another type of vegetation. Warming, water shortage and fire danger are therefore becoming mutually reinforcing pressures.
Research by Academy of Sciences scientists helps identify where action is needed and which measures are appropriate for conserving tugai. Studying plant communities and tree condition, monitoring soil moisture and salinity, and mapping sites with high fire danger make it possible to identify the most vulnerable areas. This evidence is intended to match protection and restoration to the actual needs of each place.
The first priority is to protect the natural integrity of surviving tugai and prevent further loss through land conversion. Restoration should use native species suited to local soils and moisture conditions, while natural regeneration needs protection from excessive grazing. Where feasible, the floodplain’s connection with the river and scientifically informed seasonal wetting should be restored. Whether planted trees survive subsequent hot summers must be one of the main measures of success.
These tasks are inseparable from the responsible use of the region’s water resources. Water must be conserved, losses reduced and available supplies measured more accurately, with the needs of natural ecosystems considered in water allocation. Alongside water for households, agriculture and industry, provision must be made for the flows that sustain life in river floodplains. Planting trees alone cannot save a tugai deprived of water.
For the countries of Central Asia, conserving tugai is a shared responsibility. Mountain snow and ice reserves, rivers, valleys and their wildlife are interconnected. Stronger cooperation is therefore needed in sharing scientific data, monitoring water and ecosystems, protecting habitats of rare species and restoring tugai. Each country’s practical contribution helps sustain the region’s environment.
Global climate change also requires greater solidarity from the international community. Limiting warming, expanding the use of water-saving technologies and supporting research and ecological restoration are ways for countries worldwide to help protect these unique ecosystems. Joint action for biodiversity must produce tangible results: water reaching riverside habitats, young trees growing to maturity and wildlife retaining the places it needs to survive.
The future of tugai, now reduced in many places to narrow green strips, depends on how we treat water, land and nature. Protecting it requires us to put solutions informed by science into practice together. With that commitment, life along our rivers can continue for the generations to come.
- Sh. Khabibullaev
Head of Laboratory, Institute of Botany,
Academy of Sciences of the Republic of Uzbekistan, PhD, Senior Researcher.