Tree-to-Shrub Shift Benefits the Survival of Quercus mongolica Fisch. ex Ledeb. at the Xeric Timberline

Jingyu Dai,Yang Qi,Surui Lu,Hongyan Liu

doi:10.3390/f13020244

Jingyu Dai, Yang Qi + Show 2 more

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https://doi.org/10.3390/f13020244

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Abstract

Woody species are either trees or shrubs, with the exception of approximately 9.2% “trub” species exhibiting both tree and shrub growth forms. Little is known thus far about the ecological importance of plant growth-form plasticity under a drying climate. Quercus mongolica Fisch. ex Ledeb., a dominant tree species of temperate forests in East Asia, typically shows tree-to-shrub growth-form shifts at the xeric timberline and is suitable to test whether growth-form plasticity can physiologically benefit plant drought acclimation. We quantified the tree architecture, drought stress, physiological drought tolerance, and nonstructural carbohydrates of Q. mongolica trees and shrubs on the opposite slope of the same mountain at the xeric timberline in July 2018. Compared with Q. mongolica trees on shady slopes, the shrubs on sunny slopes had less available water to use and were more severely threatened by drought. Moreover, the shrubs had stronger tolerance to drought but still tended to have less nonstructural carbohydrate accumulation. The tree-to-shrub shift effectively benefits the survival of Q. mongolica under a dry climate and may strongly contribute to forest dynamics and even fire regimes under climate drying, especially for sensitive ecosystems such as the xeric timberline, which will be vulnerable under future climate change scenarios.

Highlights

Woody plants commonly grow in either a tree form with a tall and single stem or a shrub form with multiple short basal resprouts
The ‘shrub’ plot was in a pure Q. mongolica forest without any other woody plants, while in the ‘tree’ plot, Q. mongolica occupied over 70% of the total woody plant coverage, and Populus davidiana Dode and Betula platyphylla Sukaczev existed in the forest
Q. mongolica trees were significantly taller than the shrubs (6.20 m vs. 4.30 m; p = 0.01, Forests 2021, 12, x FOR PEER REVIEWFigure 2b)

Summary

Introduction

Woody plants commonly grow in either a tree form with a tall and single stem or a shrub form with multiple short basal resprouts. Multiple potential growth forms should allow woody plants to have better environmental acclimation and survive in more diverse environments than those with weak morphological plasticity [2]. There have only been limited studies revealing how growth-form plasticity helps plants acclimate to harsh environments, such as the shrubby form that helps Acacia karroo Hayne in arid areas to prevent access to large herbivores [3]. Whether tree-to-shrub growth form transformation benefits drought acclimation of woody plants remains an open question, which needs to be addressed through combining studies from tree physiological, architectural, and environmental aspects [7,8]

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