Growth and water relations of riparian poplar forests under pressure in Central Asia's Tarim River Basin

Abstract

The riparian forests in the Tarim Basin (NW China) are mainly composed of poplar species (Populus euphratica, Populus pruinosa). In the hyper‐arid climate of this region, the trees are phreatophytes, which rely on access to groundwater. Essential ecosystem services (ESS) of these forests comprise provisioning, regulating, and cultural services. The ESS of the forests are threatened by overuse and a continuous decrease in the groundwater level due to excessive use of water for agriculture, which resulted in a severe reduction of the poplar forest area during the past decades. Studies revealed that the wood of the forests could be sustainably used through a moderate harvesting intensity. Rejuvenation of the forests from seeds is only possible after sediment deposition and wetting of the soil surface upon flooding and at relatively short distances to the groundwater. At sites with larger groundwater distances, trees can only regenerate vegetatively through root suckers emerging from underground root spacers. With increasing distance from the water table, the stands become older and sparser and, ultimately, are doomed to die off. The research results can contribute to develop suitable management schemes for the conservation and protection of Central Asia's riparian forests. The lower reaches of the Tarim River have been subjected to a water release programme for the past 20 years. We recommend focusing the diversion of such additional (“ecological”) water to stands with a short distance to the groundwater to keep these forests fully functional and to maintain their ability to regenerate from seeds.

Biogeography of global drylands

“…Their shifting sand dunes are devoid of vegetation, but more stable areas are colonized by the small halophytic tree Haloxylon ammodendron and the perennial shrub Reaumuria songarica (Gong et al ., 2019). The permanent Tarim River crosses the Taklimakan, creating the conditions for well‐developed riparian forests of Populus euphratica and Populus pruinosa (Thomas & Lang, 2021). The dryland belt of northern Eurasia also includes important arid and semiarid areas.…”

Riverine landscapes: Challenges and future trends in research and management

“…Trade‐offs existed between but also within ES categories, for example, between stagnotopic and rheotopic communities. The focus on a few dominant land use types in the catchment, such as for agricultural food production, can lead to the loss of the multifunctionality of riparian areas, as is shown by Thomas and Lang (2021). In their study in NW China, the excessive use of groundwater for agriculture resulted in severe losses of poplar forests, reducing the variety of regulating, provisioning, and cultural ES.…”

Population Structure and Spatial Distribution Pattern of Populus euphratica Riparian Forest Under Environmental Heterogeneity Along the Tarim River, Northwest China

“…Over the past decade, numerous studies examined the effects of natural flooding disturbance on the rising groundwater level, plant diversity, survival, and growth rate of the P. euphratica population within different environmental conditions ( Keyimu et al, 2017a ; Thomas et al, 2017 ; Zeng et al, 2019 ; Thomas and Lang, 2020 ). The P. euphratica occurrence has decreased with increasing distance from river channels ( Halik et al, 2006 ; Aishan et al, 2013 ; Zhang et al, 2019 ).…”