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Indirect facilitation by a liana might explain the dominance of a small tree in a temperate forest
Madrigal-Gonzalez J; Rios RS; Aragon CF; Gianoli E
Journal of Plant Ecology
Aims\r\nLianas are expected to influence composition structure and functioning of forest systems due to unequal distribution across the potential set of host plants. However our understanding of mechanisms associated with preferences for specific hosts is still limited and so is our ability to discern between endogenous and exogenous forces driving forest dynamics in the long run. In this paper we evaluated whether the dominant liana Hedera helix can indirectly contribute to the eventual dominance of the small multi-stemmed tree Corylus avellana in a remnant temperate forest in central Iberian Peninsula from comparatively reduced liana infestation on C. avellana relative to co-occurring woody species.\r\n\r\nMethods\r\nThrough principal component analysis and co-occurrence analysis we studied the distribution and spatial association between woody species and the liana H. helix. We analyzed the relationship between the number of species in a plot and the number of species infested by the liana to test the hypothesis that H. helix is a generalist liana. Through generalized linear mixed models we tested the dynamic-multi-stemmed growth form of C. avellana as a plausible life strategy to withstand in the long run the liana infestation. In particular we tested (i) the relationship between stem size and the probability of H. helix infestation including all the tree species within plots and (ii) the relationship between stem size and mortality as evidence of the stem turn over in the tree C. avellana.\r\n\r\nImportant Findings\r\nOur results indicate that H. helix and C. avellana significantly co-occur in mature stands of this remnant temperate forest where pioneer woody species are absent. Hedera helix severely infests all the woody species whenever stem size exceed ˜25 cm perimeter and there is physical contact at the base of the stem. This implies that all the trees in the community are potential hosts for H. helix. Mixed models indicate that both infestation by H. helix and stem mortality are positively related to C. avellana stem perimeter. Reduced long-term infestation of the liana by means of a multi-stemmed growth form with high stem turnover in C. avellana might be an advantage with respect to unipodial tree species. Thus the liana-tree coexistence pattern may be interpreted as an indirect positive interaction that contrary to previous findings results here in species dominance instead of species coexistence.
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