Shade tolerance, canopy gaps and mechanisms of coexistence of forest trees

Gravel, Dominique; Canham, Charles D.; Beaudet, Marilou et Messier, Christian (2010). « Shade tolerance, canopy gaps and mechanisms of coexistence of forest trees ». Oikos, 119, pp. 475-484.

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The belief that canopy gaps are important for the maintenance of tree species diversity appears to be widespread, but there have been no formal theoretical models to assess under what conditions gap phase processes allow coexistence. Much of the empirical research on niche diff erentiation in response to gaps has focused on evidence for an interspecific tradeoff between low light survival and high light growth. The objectives of this study are first to distinguish the possible mechanisms allowing coexistence based on this tradeoff, and second, to explore their limitations. We present a theory of forest dynamics driven by small-scale disturbances as a special case of the theory of coexistence in variable environments. We demonstrate that temporal and spatial heterogeneity in light conditions that results from canopy gaps can allow stable coexistence as a result of three previously documented general mechanisms: ‘relative non-linearity’, ‘the successional niche’ and the ‘storage eff ect’. We find that temporal fluctuations in light availability alone allow the stable coexistence of only two species. Spatial variation in disturbance synchronicity and intensity allows three species to coexist in a narrow parameter space. The rate of extinction is, however, extremely slow and there is transient coexistence of a larger number of species for a long period of time. We conclude that while the low light survival/high light growth tradeoff may be ubiquitous in forest tree species, it is unlikely to function as an important mechanism for the stable coexistence of several tree species.

Type: Article de revue scientifique
Mots-clés ou Sujets: Shade tolerance, canopy gaps, coexistence
Unité d'appartenance: Faculté des sciences > Département des sciences biologiques
Déposé par: Christian Messier
Date de dépôt: 23 août 2010 13:02
Dernière modification: 01 nov. 2014 02:15
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