Fine Root Distribution in Dehesas of Central-Western Spain |
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Authors: | G Moreno JJ Obrador E Cubera C Dupraz |
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Institution: | (1) I.T.Forestal, Centro Universitario, UEX, Plasencia, Cáceres, 10600, Spain;(2) INRA, UMR-SYSTEM, 34060 MONTPELLIER, Cedex, France |
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Abstract: | A Dehesa is a structurally complex agro-silvo-pastoral system where at least two strata of vegetation, trees and herbaceous
plants coexist. We studied the root distribution of trees (Quercus ilex L.) and herbaceous plants, in order to evaluate tree and crops competition and complementarity in Dehesas of Central Western
Spain. 72 soil cores of 10 cm diameter (one to two metre deep) were taken out around 13 trees. Seven trees were intercropped
with Avena sativa L. and six trees were in a grazed pasture dominated by native grasses. Soil coring was performed at four distances from the
tree trunks, from 2.5 (beneath canopy) till 20 m (out of the canopy). Root length density (RLD) of herbaceous plants and trees
was measured using the soil core-break method. Additionally, we mapped tree roots in 51 profiles of 7 recently opened road
cuts, located between 4 and 26 m of distance from the nearest tree. The depth of the road cuts varied between 2.5 and 5.5 m.
Herbaceous plant roots were located mostly in the upper 30 cm, above a clayey, dense soil layer. RLD of herbaceous plants
decreased exponentially with depth until 100 cm depth. Holm-oak showed a much lower RLD than herbs (on average, 2.4 versus 23.7 km m−3, respectively, in the first 10 cm of the soil depth). Tree RLD was surprisingly almost uniform with depth and distance to
trees. We estimated a 5.2 m maximum depth and a 33 m maximum horizontal extension for tree roots. The huge surface of soil
explored by tree roots (even 7 times the projection of the canopy) could allow trees to meet their water needs during the
dry Mediterranean summers. The limited vertical overlap of the two root profiles suggests that competition for soil resources
between trees and the herbaceous understorey in the Dehesa is probably not as strong as usually assumed. |
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Keywords: | Agroforestry core-break method grasses open woodland Quercus ilex root length density |
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