Structural dynamics of Populus euphratica forests in different stages in the upper reaches of the Tarim River in China

Abstract

We selected four Populus euphratica Oliv. forest plots (100 m × 100 m) in the upper reaches of the Tarim River in the Xinjiang Uygur Autonomous Region of China. Each of the four forest plots was chosen to represent a different growth and death stage of P. euphratica forest: juvenile forest, mature forest, dying forest, and dead forest. In each plot, we measured the coordinates, DBH, height, and status of all P. euphratica individuals. We used (1) spatial pattern analysis to explore spatial distribution patterns and associations of live trees and dead trees, (2) a random mortality model to test whether the tree death was random or non-random, and (3) a generalized linear mixed-effect model (GLMM) to analyse factors related to tree survival (or death). In the juvenile plot, live trees were significantly aggregated at all scales (p < 0.05); while in the mature and dying plots, live trees were more aggregated at small scales and randomly distributed at larger scales. Live trees and dead trees showed a significantly positive association at all scales in the juvenile plot (p < 0.05). While in the mature and dying plots, live trees and dead trees only showed a significantly positive association at scales of 0-3 m (p < 0.05). There was significant density-dependent mortality in the juvenile plot; while mortality was spatially random at all scales in the mature and dying plots. The distance from the river showed significantly negative correlations with tree survival (p < 0.01). DBH and height had significantly positive associations with tree survival in the juvenile, mature, and dying plots (p < 0.05). In extreme drought, dying trees appeared to be shape-shifting into more shrub-like forms with clumps of root sprouts replacing the high canopies. The shift under extreme drought stress to more shrub-like forms of P. euphratica may extend their time to wait for a favourable change.Populus euphratica Oliv., the desert poplar, is a prominent component of Tugai floodplain ecosystems along river valleys in arid and semi-arid regions with a very wide range, occurring naturally from North Africa, across the Middle East and Central Asia to western China 1,2 . The P. euphratica forests, which are also known as Tugai forests, are the main component of the desert riparian vegetation in Central Asian inland rivers. These P. euphratica forests provide an important habitat for plants and animal life and harbour the highest plant biodiversity in desert regions [3][4][5] , which is likely also to enhance local biodiversity of animals, such as birds and insects. Additionally, these Tugai forests provide major natural resources (timber, fuelwood, livestock fodder, etc.) and provide critical environmental benefits such as increasing watershed protection, including stabilization of riverbanks and providing windbreaks to reduce erosion of sand and soil 1,4,6 .The expansion and decline processes of P. euphratica forests are closely related to hydrological events (e.g., river diversion, variation of river discharge, and groundwater depth) coupled...

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

“…This was also true for the ANN, DMI, and I δ indexes ( Table 3 ). These observations agree with previous work findings reported by Zhang et al (2019) and Miao et al (2020) , which showed that in the upper reaches of the Tarim River, the P. euphratica live trees were typically randomly distributed. The trees in the middle reaches were unevenly distributed, except for two plots (M1 and M2) closest to the river ( Figure 5 ), with the g( r ) function producing high values above the CSR null model confidence interval.…”

“…Various traditional field measurement methods have been used for analyzing the spatial distribution pattern of riparian forests ( Han et al, 2014 ; Xu et al, 2016 ; Miao et al, 2020 ). However, traditional methods are hard to obtain detailed structural parameters, and spatial distribution patterns of the forest stand in the same period, which hindering our deeper understanding of forest structure.…”

“…The growth of P. euphratica highly depends on the groundwater and soil moisture ( Halik et al, 2009 ; Keyimu et al, 2017a ). Under extreme drought stress, morphological characteristics of trees shift the form to extend their survival period to wait for a favorable change ( Miao et al, 2020 ). Monda et al (2008) demonstrated near mature P. euphratica trees at the Heihe River to exhibit damage at the top part of the crown, while the dieback phenomenon was observed, suppressing their height.…”

“… Zeng et al (2019) studied different age class tree distribution and found the spatial patterns of young and old P. euphratica trees in the upper reaches of the Tarim River exhibit aggregated and random distribution. Miao et al (2020) investigated the spatial distribution of live and dead trees of P. euphratica in the upper reaches and found that they showed a positive association in the juvenile plot. Most of the studies focused on investigating the spatial distribution of P. euphratica in the upper or middle reaches of the Tarim River via traditional field survey methods ( Bai et al, 2013 ; Xu et al, 2016 ; Zhou et al, 2018 ).…”

High-throughput sequencing reveals rhizosphere fungal community composition and diversity at different growth stages of Populus euphratica in the lower reaches of the Tarim River

“…However, some researchers indicated that P. euphratica population regeneration in the lower reaches of Tarim River showed a decline type, the proportion of young plants in the population decreased significantly or even lacked, population was mostly over mature forest plants and the overall performance of the decline trend ( Zhou et al, 2018 ). Currently, most studies of P. euphratica were focus on heteromorphic leaves ( Li et al, 2020a ; Li et al, 2020b ), photosynthetic physiological characteristics ( Wang et al, 2014 ), water use efficiency ( Zhou et al, 2019 ), population structure ( Miao et al, 2020 ), etc , while few studies on the relationship between plant and rhizosphere soil fungal community composition and diversity. Therefore, the goal of our work was to (1) analyze the composition and diversity of rhizosphere soil fungi of P. euphratica at different growth stages in the lower reaches of the Tarim River; (2) explore the dominant fungi in the P. euphratica rhizosphere at different stages, and the change of rhizosphere soil physical and chemical properties; (3) elucidate the correlation between fungal community composition and environmental factors.…”