Introducing resprouters to enhance Mediterranean forest resilience: importance of functional traits to select species according to a gradient of pine density.

Resprouter species are important for Mediterranean ecosystem resilience, but they are scarce in landscapes dominated by pioneer pines. Sound knowledge of resprouter seedling functional responses and establishment success across different pine habitats would help guide forest restoration efforts., Four broadleaved resprouter species, that is two shrubs - Arbutus unedo and Pistacia terebinthus - and two trees - Fraxinus ornus and Sorbus domestica - were planted under an experimentally created gradient of pine cover from totally open conditions to dense pine cover., Seedling survival and growth were monitored for 5 years. Phenological, physiological and morphological traits were measured to gain insight into the mechanisms of pine-seedling interaction., Interaction outcomes varied according to species identity, pine cover treatment and time. Light-to-moderate pine cover induced greater height growth and little or no effects on diameter and survival of the two trees. Competition was always detected for shrubs, whereas competition and facilitation were noted for trees. Within pine stands, negative interactions increased with tree cover, making dense stands the most limiting. Interactions were only detectable after 2-3 years, but increased in intensity with time., Functional responses to increasing pine cover indicated a seedling strategy of carbon gain optimization in the shade (increased specific leaf area and leaf area, decreased leaf dry matter content), particularly in tree species seedlings. Increasing pine cover induced higher water stress, but lower photochemical stress. The deciduous species had a longer vegetation season under pine canopies, whereas the evergreen shrub Arbutus unedo showed a lower polycyclism rate and flower production., Synthesis and applications. Moderate pine cover facilitates the establishment of deciduous trees at the expense of shrubs. This pattern can be attributed to a higher shade tolerance of the trees than the shrubs combined with a low tolerance of trees to photoinhibition. We therefore recommend using evergreen shrubs for the restoration of open land and high-specific-leaf-area deciduous trees for pine stand diversification. However, in dense forests, thinning is needed to increase light availability prior to seedling introduction. [ABSTRACT FROM AUTHOR]