Data from: 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, i.e. 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 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 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.

萌蘖物种（resprouter species）对地中海生态系统的恢复力至关重要，但在先锋松占主导的景观中，这类物种极为稀缺。深入了解不同松树林生境下萌蘖幼苗的功能响应与定植成功率，将有助于指导森林修复实践。本实验选取4种阔叶萌蘖物种，包括2种灌木：草莓树（Arbutus unedo）与乳香黄连木（Pistacia terebinthus），以及2种乔木：花梣（Fraxinus ornus）和欧山茱萸（Sorbus domestica），将其种植于人工构建的松覆被梯度生境中，生境范围涵盖完全开阔至高密度松林两种极端条件。研究对幼苗的存活与生长状况进行了为期5年的监测，并通过测定物候、生理及形态性状，深入解析松树与幼苗间的互作机制。互作效应因物种属性、松覆被处理及监测时间而异。轻度至中度的松覆被可促进两种乔木的株高生长，而对其地径生长与存活率几乎无影响；灌木始终面临种间竞争，而乔木则同时受到竞争与促进作用的双重影响。在松林内部，负向互作效应随松覆被占比升高而增强，高密度松林因此成为幼苗定植的最限制性生境。互作效应仅在种植后2-3年才可被观测到，且其强度随监测时长增加而不断提升。幼苗对松覆被升高的功能响应表明，其采取了遮阴环境下的碳获取优化策略：比叶面积（specific leaf area）与叶面积升高，叶干物质含量降低，这一现象在乔木幼苗中尤为显著。松覆被升高会加剧幼苗的水分胁迫，但同时降低其光化学胁迫程度。落叶物种在松林冠层下的营养生长期更长，而常绿灌木草莓树（Arbutus unedo）的多次开花率与开花量均更低。结论与应用建议：中度松覆被可促进落叶乔木的定植，但会抑制灌木的存活。该现象可归因于乔木相较灌木具有更高的耐阴性，同时乔木对光抑制（photoinhibition）的耐受性较低。据此，我们建议在开阔生境的修复中选用常绿灌木，而在松林群落多样化改造中选用高比叶面积的落叶乔木。但在高密度松林内，需先通过间伐提升光照条件，再进行幼苗定植。