The coexistence of forest tree species has often been linked to differences in their response to light availability during the regeneration stage. Van Couwenberghe et al. study natural regenerated shade-tolerant Fagus sylvatica and shade-intermediate Quercus petraea seedlings and find that no rank reversal occurs between the two species along a light gradient, or along density, mixture or seedling-size gradients. The results thus do not support the classical assumption that spatial heterogeneity in a canopy opening would explain the coexistence of the two species studied. Instead, it is suggested that the main driver of the dynamics of these mixed stands is spatial variation in local size hierarchies among seedlings, which may be caused by differences in seedling emergence time or initial seedling performance.
Early life-history stages of cacti can benefit from the facilitative effects of nurse plants that reduce solar radiation and water stress. Miranda-Jácome et al. conduct a reciprocal transplant experiment, coupled with the artificial manipulation of sun/shade conditions, to test for the effects of local adaptation on germination, seedling survival and growth of the columnar cactus Pilosocereus leucocephalus. They find that significant local adaptation is mainly detected under full sunlight conditions, indicating that sun/shade acts as a selective agent in water-limited environments. Facilitation provided by nurse plants in these environments can attenuate the patterns of local adaptation among plants benefiting from nurse plant effects.