Tree morphology responds to neighbourhood competition and slope in species-rich forests of subtropical China |
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| Authors: | Anne C Lang Werner Härdtle Helge Bruelheide Christian Geißler Karin Nadrowski Andreas Schuldt Mingjian Yu Goddert von Oheimb |
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| Institution: | 1. Leuphana University Lüneburg, Institute of Ecology and Environmental Chemistry, Scharnhorststr. 1, D-21335 Lüneburg, Germany;2. University of Halle, Institute of Biology/Geobotany and Botanical Garden, Am Kirchtor 1, D-06108 Halle, Germany;3. University of Tübingen, Institute of Geography, Rümelinstraße 19-23, 72070 Tübingen, Germany;4. University of Leipzig, Special Botany and Functional Ecology, Johannisallee 21-23, 04103 Leipzig, Germany;5. College of Life Sciences, Zhejiang University, Hangzhou 310058, China |
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| Abstract: | Trees are able to respond to their local biotic and abiotic environment with morphological adjustments which improve resource acquisition and, thus, growth. In forests, light is broadly recognised as one of the major factors determining growth, and morphological responses comprise changes in crown architecture and stem stature. On sloping terrain, the interplay of phototropism and gravitropism may further affect morphological growth characteristics. However, different tree species are expected to show species-specific responses. In this study, we analysed three growth characteristics of tree individuals belonging to four species of two functional groups (evergreen: Schima superba, Castanopsis eyrei, deciduous: Quercus serrata var. brevipetiolata, Castanea henryi) in a species-rich Chinese subtropical forest. Crown projection area, relative crown displacement and stem inclination were related to biotic (local species richness, functional richness, competition, stand age) and abiotic (slope aspect and inclination, soil depth) variables in the local neighbourhood of the tree individuals. We hypothesised that (i) there are species-specific differences in the morphological response of crown architecture and stem stature and (ii) that crown size and asymmetry as well as stem inclination are influenced by both, biotic and abiotic factors. In contrast to our expectations we were unable to reveal any species-specific differences in any of the three growth characteristics. The results of mixed effects models showed that crown area was mainly affected by the target tree's dbh and biotic variables related to neighbours (competition, functional diversity), whereas stem inclination was mainly influenced by slope. Relative crown displacement was influenced by both, biotic and abiotic variables. We conclude that growth responses resulting in crown displacement and stem inclination seem to be an important mechanism to ameliorate foraging for light in our study area, but that these responses appear to be species-independent. The interplay of stem inclination and crown displacement allows for a plastic response of tree individuals in biotically and abiotically heterogeneous environments. Our results indicate that forest management in this region should focus on functionally diverse stands which are promoting crown area positively resulting in increased growth rates of individual trees. |
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| Keywords: | Gutianshan National Nature Reserve Stem inclination Crown displacement Crown projection area Functional diversity |
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