The role of shade in maintaining alternative stable states between open- and closed-canopy vegetation

Fire is commonly identified as strong driver of alternative stable states such as adjacent open- versus closed-canopy vegetation types. The absence of open-canopy species from closed-canopy understoreys, where light availability is low and dynamic, however, suggests shade tolerance is an integral determinant of such vegetation boundaries. While the importance of light dynamics between alternative stable states has been acknowledged, the physiological mechanisms behind sun versus shade-tolerance are unclear. Here we investigated the differences in light interception and carbon assimilation of open- and closed-canopy species, and whether this contributes to the maintenance of alternative stable states.

Evergreen forest and fynbos species were grown under three light availability treatments (24%, 54%, 100%) in a glasshouse with their photosynthetic response to continuous and fluctuating light, dark respiration, root respiration, biomass and leaf traits quantified.
 
Fynbos species dis...