Disentangling canopy and soil effects of a savanna tree species on its understorey

QUESTIONS: What are the relative contributions of short‐term canopy and long‐term soil effects of a savanna tree species in explaining differences in biomass, species density and composition of understorey plants (1) between trees and open areas, and (2) below trees between the northern and sout...

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Bibliographic Details
Published in:Journal of vegetation science 2016-07, Vol.27 (4), p.771-779
Main Authors: Abdallah, Fathia, Richard Michalet, Jean‐Paul Maalouf, Saad Ouled‐Dhaou, Blaise Touzard, Zouhaier Noumi, Mohamed Chaieb
Format: Article
Language:English
Subjects:
Acacia tortilis
biomass
canopy
Competition
disturbed soils
ecosystems
environmental factors
Facilitation
ions
landscapes
Life Sciences
microclimate
national parks
nutrients
Savanna
savannas
shade trees
soil analysis
soil crusts
species diversity
temperature
Tunisia
Understorey community
understory
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Summary:QUESTIONS: What are the relative contributions of short‐term canopy and long‐term soil effects of a savanna tree species in explaining differences in biomass, species density and composition of understorey plants (1) between trees and open areas, and (2) below trees between the northern and southern sides of the trees? LOCATION: Acacia tortilis tree savanna ecosystem, southern arid Tunisia (Bou Hedma National Park). METHODS: We measured environmental conditions (soil and microclimate) on the northern and southern sides of the trees and in open areas between trees. We also manipulated light on the southern side of the trees with a shade cloth, and cross‐transplanted soils between north and south sides of the trees while testing for soil disturbance. The response of the vegetation was analysed with CCA and univariate analyses. RESULTS: Differences in species composition, richness and biomass of understorey communities between trees and open areas were mostly due to long‐term soil effects of A. tortilis, mainly nutrients and water, whereas differences below trees were due to short‐term effects of the trees, in particular on light and temperature conditions. Additionally, the soil disturbance induced by our soil transplantation treatment modified species composition and density, likely because of disruption of the soil crust. CONCLUSIONS: Our study provides additional evidence that savanna trees have the potential to increase the diversity of arid systems at the landscape level. We showed that two main mechanisms are involved: (1) trees improve soil conditions, in particular nutrients and water, resulting in differences between trees and open areas; (2) within trees, there is heterogeneity of light and temperature conditions under the crown, resulting in vegetation differences.
ISSN:1100-9233
1654-1103
DOI:10.1111/jvs.12402