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

Ning Miao,Bin Hu,Zhijun Li,Maoping Li,Wenjing Tao,Timothy C Moermond,Peipei Jiao

doi:10.1038/s41598-020-60139-7

Ning Miao, Bin Hu + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-60139-7

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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.

Highlights

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]
We focused on sites of relatively undisturbed P. euphratica forest and addressed the following questions: (1) is tree mortality random or non-random over different growth and death stages; (2) in the different stages of P. euphratica forests, how do spatial patterns of live and dead trees change through time; and (3) which attributes are related to the survival and death of P. euphratica in the different stages of P. euphratica forests
In the mature and dying forest plots, mortality was spatially random at all scales (Fig. 8B,C), i.e., dead trees did not change the spatial distribution patterns of live trees, indicating that tree death was in effect a random event and generally unrelated to density-dependent effects in the mature forest and dying forest stages

Summary

Introduction

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]. Under high drought stress conditions in the dying and dead forest plots, the T. ramosissima shrubs were clearly surviving better than the P. euphratica trees.

Results

Conclusion