Taklimakan Desert—Populus euphratica Forests

Description

The nominated site is the most typical warm temperate desert in the world. The Taklimakan Desert is located in the largest inland basin in China-the Tarim Basin, which is with an area of 560,000 km², and surrounded by the Tianshan Mountains, the Kalakunlun Mountains, and the Kunlun Mountains. The whole length from east to west is 1000 km, and the width from south to north is 400 km, with an area of 337, 600 km². Taklimakan Desert is the largest desert in China and second largest in the world. Taklimakan Desert is a temperate desert, which belongs to typical continental climate. The temperature changes greatly and annual precipitation is low. The average temperature of July is 25 ℃, and that of January is about -9 ~ -10 ℃. The highest temperature is 45.6 ℃ in summer (recorded in 1997), and the lowest below -20 ℃ in winter. Diurnal temperature difference reaches over 40 ℃. The annual precipitation is less than 100 mm, while evaporation reaches 2500-3400mm. Sand movements are frequent and intense throughout the year. The sandstorm days make up one third of a year, and maximum wind speed is up to 300m/s. The geography of the sand dunes in the nominated site is complicated and includes many dune types, for example, crescent dunes, dome-shaped dunes, honeycomb-like dunes, beam-like dunes, dendritic sand dunes, composite longitudinal sand ridge, fish scale-shaped dunes and pyramid-shaped dunes etc. The average height of sand dunes is 100-200m, maximum reaches 300m. The mobile dunes cover over 80% area of Taklimakan Desert. According to research, the low sand dunes move about 20 m/y. The desert has extended about 100 km southward during the last thousand years. There are high mountain chains that enclose the basin and help to create the extremely arid desert climate in which this most typical warm temperate desert environment has been formed.

The nominated area includes the largest exotic (flowing into the inland basin) river of China. The Tarim River is the longest inland river of China, as well as being a famous river that flows into an arid basin. One-hundred-and-forty-four tributaries, attributed to 9 large water systems of the Tianshan and Kunlun Mountains, converge into the Tarim River. The Tarim River runs through the Taklimakan Desert and terminates at Lop Nur. At peak flow, it has a length of 2179 km and a main trunk of 1321 km, with and drainage area of 0.102 billion ha. The Tarim River is famed for its prominent regional character as well as its environment, including large stands of Euphrates poplar trees Populus euphratica. However, during the past 50 years, because of immoderate utilization of water resources by humans, water flows have been reduced in parts of the Tarim River, causing die-offs of poplar trees. At the same time, desertification has been more intensive, biodiversity has been threatened, the ecological barriers against the desert has been weakened and environmental challenges such as airborne dust and dust storms have become more frequent, with implications for the development of human society and economy. Fortunately, since 1990, steps have been taken to address these problems. Increased awareness of the need for environmental protection, the establishment of nature reserves and the implementation of enhanced water management, have enabled the poplar trees to thrive.

The nominated area has "living fossils" that date back to the Tertiary period.  The poplar trees in the vicinity of the Tarim River are the oldest poplar trees in the world, emerging with the upheaval of the Qinghai-Tibet plateau. This kind of poplar tree has existed for more than 60 million years. Fossils of this kind of poplar tree have been discovered in the strata of the Tertiary Oligocene located at Kuqa Thousand-joss Cave and Dunhuang Blacksmith Grove. These fossils are about 3-6 million years old. These fossil trees have physiological characteristics that make them very hardy, enabling them to withstand both chilling winters and broiling summers, aridity, waterlogging and high saline-alkali concentrations. Poplar trees are dioecious (self-propagating) plants that produce globular pollen that take root when they meet water. They also have heteromorphism (i.e. the character of the leaves changes with the age of the tree) and an extensive root network with strong ability to absorb water and withstand salt. The trees grow fast when there is enough water and the growth rate decelerates when the water resource is scanty. There is an old saying that poplar trees can thrive for 1000 years, stand firmly for 1000 years after their death and fail to rot after falling down.

The nominated area contains the typical ecosystems of temperate arid deserts. According to recognized global bio-geographical systems (Udvardy 1975), the nominated heritage is a typical representative of the Taklimakan - Gobi Desert Biogeographical Province, and the important bird area (CN115) of Taklimakan Desert within the system of 218 IBAs recognized by Birdlife International in China. Various ecological systems are found in the nominated site, such as typical desert ecosystems, wetland ecosystems and forest ecosystems. The plant and animal species within the poplar forest ecosystem are rare and the poplars are the only tall trees in this ecosystem. The companion plants are mainly halophytes and xerophytic plants, represented by Elaeagnus angustifolia L, Tamarix chinensis, Apocynum venetum, Halimodendron halodendron, Alhagi sparsifolia, bullrush and liquorice etc. The Ferruginous pochard Aythya nyroca, Black-necked grebe Podiceps nigricollis, Black Stork Ciconia nigra, Little bittern Ixobrychus minutus, and the Tarim Yarkand hare Lepus yarkandensis are among local species identified in the IUCN red list as threatened species. The big-head fish of the Tarim River is a national first-level protected animal of China and Tarim Red deer Cervus elaphus yarkandensis is endemic to this region. The poplar forests can be divided into four formations: young poplar trees on the floodplain, bullrush-jarrah-poplar mix, jarrah-poplar combination, and grass-wild hemp- Halimodendron halodendron,- poplar stands. The poplar forests can be divided into five age-types according to the growth stage i.e. relatively young forest, full-blown forest, excessively mature forest, old forest and withered forest. Poplars are distributed throughout the nominated site with ages ranging up to one thousand years old. The diameter at breast height of poplar trees is between 1cm and 2.7 m. The poplar trees indicate different forests forms with their different ages.

The nominated site has the largest distribution zone of natural euphrates poplars in the world. The Tarim Basin is the world's core area of these poplar trees which cover 352,200 ha, accounting for 90% of their total area in China and 54.29% of the global distribution. The largest natural poplar trees in the world occur in the Tarim River drainage area and large areas of undisturbed poplar forests have been preserved in this region. According to the investigations of Chinese scientists, the continuous distribution of natural poplar forest in the Tarim Basin covers millions of acres, and the volume of wood reaches over 1.5 million square kilometers.

The nominated area records the changing history of the Tarim River. The three main distributional types of natural poplar forests are as follows: the terrace along the river bank, the front edge of the diluvial fan where underground water surfaces, and the regions around lakes and wetlands. The distribution of Tarim poplar trees is mainly discontinuous in a corridor along the river banks. The distribution reflects the temperature, water and edaphic conditions and shows the narrow environmental conditions in which the poplars thrive. There are more than ten belts of poplar forests of differing ages along both the south and north banks of the Tarim River in the nominated site. The belts vary from hundreds of meters to several kilometers in width. The withered poplar forest belts and living poplar belts alternate with each other, reflecting the vicissitudes of the Tarim River.

Justification of Outstanding Universal Value

The poplar forest contains a significant species and gene pool of the temperature desert zone. Poplar trees date from the Tertiary and, therefore, have been regarded as living fossils of ancient species by botanists. They bear genes that endows them with the adaptation to withstand chilling winters and broiling summers, aridity and waterlogging, saline-alkali concentrations. Thus, these ancient rare trees, which possess great resilience, can be regarded as an invalauble natural gene pool. The specialists on forest genetics from FAO have regarded these poplar trees as the forest gene resource that demands the most crucial conservation in arid and semi-arid zones on the globe.

The poplar forests are important for maintaining the ecological equilibrium of the Tarim River. Poplar forests are the dominant species of the desert ecosystem in the temperate arid zone. They are fundamental for maintaining the stability of the river-bank forest in arid zones. Poplar forests have the ability to conserve the water resource and provide appropriate habitats for various other plants. They also provide favorable habitats and food resources for micro-organism and animals and the setting in which they can exist and propagate their population. Regions with abundant water and flourishing forest are the migration channels of migratory birds and wild animals. Thus, poplar trees enhance the complicated structure of the food chains of oasis ecosystems and contribute to the stability of oases. The poplar tree ecosystem plays an important part in fixing sand dunes, holding back desertification, alleviating dust storms, conserving biodiversity and improving the environment.

Poplar stands are an ecological barrier against dust storms. They have strong roots and the main roots reach depths of 6-8 m. Horizontally, the roots may extend for tens of meters. These attributes ensure that enough water can be absorbed by the tree. The root can also absorb salt from the soil to increase the osmotic pressure across the cell wall, which enhances the ability to absorb water and prevents salinization. Even if the main trunk is totally withered, the root can catch hold of the soil and sand firmly. Therefore, poplar trees possess a powerful ecological ability to maintain water and soil, as well as withstanding storms and fixing sand dunes. The lower reaches of the Tarim River are located between the Taklimakan and Kumtage Deserts, which are divided by a green corridor made up of poplar trees. The Loess Plateau, the edge of Taklimakan and the region around the Salty Sea are a huge source of dust for storms in the northern hemisphere. Therefore, preserving the poplar forest will play a key role in alleviating dust storms in the world. The terminal of the Tarim River has receded from the expansive Lop Nur to Taitema Lake, and the latter has shrunk in most recent years. This reflects the environment vicissitudes in the recent hundreds of years, both natural and human-induced, and provides important scientific evidence for research on global climate change and associated human impacts.

Taklimakan is the drought centre of the Eurasian continent. Influenced by uplifting of the Qinghai-Tibet Plateau, the Taklimakan Desert plays a special role in the northern hemisphere, for research on circulation systems of land-sea, land-land and environmental effects of the Qinghai-Tibet Plateau, which is irreplaceable. Strong wind and resourceful sand form various sand dune types and patterns in the Taklimakan Desert. It is the world museum of sand dunes, which is natural laboratory for research into the regulation of environment and mechanics of sand movement.

Statements of authenticity and/or integrity

The nominated heritage involves the essential segment of the middle reaches of the Tarim River and it is in this region that the poplar forest is the tallest and densest, and exhibits the least human interference. The area of the nominated site is large enough to encompass a wide variety of vital ecological processes, particularly as the population in the nominated site is small and human beings have yet to have much impact on the natural ecosystem. The nominated site includes the Xinjiang Tarim National Nature Reserve and the regional Populus EuphraticTrees Forest Nature Reserve, which are under the protection of relevant national laws. Local management organizations are already in place to ensure the resource conservation of the nominated site. In 2001, a comprehensive management plan was complemented for the Tarim River drainage area for the possible construction of a major national project. The water resource has been distributed and utilized in a reasonable way. Sufficient water is delivered downstream to maintain ecological processes and 0.2 million ha are irrigated. Thus, the poplar forest in the nominated site has been well protected.

Comparison with other similar properties

No natural heritage area of Euphrates poplar forest currently exists on the World Heritage List and this type of arid desert ecosystem is also an unrepresented ecological system. Such poplar forests are mainly distributed in central and western Asia, northern Africa and part of southern Europe, around 30°-50°N. The distribution zone crosses over 20 countries. The total area of these poplar forests in the world is about 648, 711 ha. Because of human interference, poplar forests in many countries have been destroyed, leaving only sparse and degraded forests. Nowadays, the largest original poplar forests in the world are concentrated in China and some mid-Asian countries like Kazakstan. The area of Euphrates poplar forests in China is 395,200 ha and this accounts for 61% of the total area in the world. Such forests are found in China in the western five provinces and western Inner Mongolia. Xinjiang accounts for about 90% of the total area of such forests in China. The largest and best formed example of original poplar forest in the world occurs in the Tarim River drainage area and it has suffered little from human interference and is well preserved in this region. The nominated site is the most prominent representative of natural poplar forests and it cannot be matched elsewhere in the world.