Facilitation in plant communities: the past, the present, and the future

  1. Figure 1

    Figure 1
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    Figure 1

    Examples of mechanisms of plant–plant facilitation. (a) Buffered substrate and air temperature, enhanced soil moisture and nutrient content. Cushion of Azorella monantha harbouring native and invasive species (e.g. the Andean cauliflower Nastanthus agglomeratus and the field chickweed Cerastium arvense, respectively) at the upper limit of vegetation (3600 m a.s.l) in the high Andes of central Chile. Photo: Lohengrin A. Cavieres (see Cavieres et al. 2005, 2007). (b) Protection from drought. Adult individual of the tussock grass Stipa tenacissima facilitating a sapling of Pinus halepensis in a semi-arid steppe, south-east Spain. Photo: Fernando T. Maestre (see Maestre et al. 2001, 2003a). (c) Protection from browsing. Quercus pubescens seedling within unpalatable Buxus sempervirens shrubs, southern France. Photo: Georges Kunstler (see Kunstler et al. 2006). (d) Protection from browsing and drought. Facilitation by Gymnocarpos decander of annual vegetation in a semi-arid environment, Jordan. Photo: Pierre Liancourt.

  2. Figure 2

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    Figure 2

    The number of papers examining facilitation (open bars) and competition (closed bars) as a percentage of the total number of papers published in five leading plant ecology journals (American Naturalist, Ecology, Journal of Ecology, Oikos and Oecologia) between 1995 and 2006. Data obtained from ISI Web of Knowledge (http://portal.isiknowledge.com/; 1 March 2007) using the search strings [(‘positive interaction*’ OR facilitation) AND plant*] or alternatively [(‘negative interaction*’ OR competition) AND plant*], specifying English language articles only. After Dormann & Brooker (2002).

  3. Figure 3

    Figure 3
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    Figure 3

    Indirect (dotted line) and direct (solid line) interactions in a complex system. (a) Species A suppresses species B, which affects the potential negative effect of species B on C. As suggested by Levine (1976), if the benefit from suppression is higher than the direct negative effects, indirect facilitation occurs in the community. However, the benefit from suppression can be outweighed by direct negative effects, resulting in no net indirect facilitation (Levine 1999; Pagès et al. 2003). (b) Non-transitive interactions (A > B, B > C, C > A). The suppression of species B by A causes an indirect facilitation of species C, which increases its negative effect on A. In such a system the species ameliorate each other's effects and contribute to long-term coexistence (Czaran et al. 2002; Callaway & Howard 2006).