Small‐scale genetic structure and mating patterns in an extensive sessile oak forest (Quercus petraea (Matt.) Liebl.)

Oaks (Quercus) are major components of temperate forest ecosystems in the Northern Hemisphere where they form intermediate or climax communities. Sessile oak (Quercus petraea) forests represent the climax vegetation in eastern Germany and western Poland. Here, sessile oak forms pure stands or occurs intermixed with Scots Pine (Pinus sylvestris). A large body of research is available on gene flow, reproduction dynamics, and genetic structure in fragmented landscapes and mixed populations. At the same time, our knowledge regarding large, contiguous and monospecific populations is considerably less well developed. Our study is an attempt to further develop our understanding of the reproduction ecology of sessile oak as an ecologically and economically important forest tree by analyzing mating patterns and genetic structure within adult trees and seedlings originating from one or two reproduction events in an extensive, naturally regenerating sessile oak forest. We detected positive spatial genetic structure up to 30 meters between adult trees and up to 40 meters between seedlings. Seed dispersal distances averaged 8.4 meters. Pollen dispersal distances averaged 22.6 meters. In both cases, the largest proportion of the dispersal occurred over short distances. Dispersal over longer distances was more common for pollen but also appeared regularly for seeds. The reproductive success of individual trees was highly skewed. Only 41 percent of all adult trees produced any offspring while the majority did not participate in reproduction. Among those trees that contributed to the analyzed seedling sample, 80 percent contributed 1-3 gametes. Only 20 percent of all parent trees contributed four or more gametes. However, these relatively few most fertile trees contributed 51 percent of all gametes within the seedling sample. Our study demonstrates that extensive, apparently homogenous oak forests are far from uniform on the genetic level. On the contrary, they form highly complex mosaics of remarkably small local neighborhoods. This counterbalances the levelling effect of long-distance dispersal and may increase the species’ adaptive potential. Incorporating these dynamics in the management, conservation and restoration of oak forests can support the conservation of forest genetic diversity and assist those forests in coping with environmental change.

栎属（Quercus）植物是北半球温带森林生态系统的核心组成部分，它们在其中构成演替中期或顶极群落。无梗花栎（Quercus petraea）林是德国东部与波兰西部的顶极植被类型。在此生境中，无梗花栎可形成纯林，或与苏格兰松（Pinus sylvestris）混生。目前已有大量研究聚焦于破碎化景观与混合种群中的基因流、繁殖动态以及遗传结构，但针对大型连续单优种群的相关认知则相对匮乏。本研究以一片广袤的天然更新无梗花栎林为研究对象，通过分析其成年个体与1-2次繁殖事件产生的幼苗的交配模式与遗传结构，以期加深对这种兼具生态与经济价值的森林树种——无梗花栎繁殖生态学的认知。研究发现，成年个体间的正向空间遗传结构可达30米，幼苗间的则可达40米。种子扩散距离的平均值为8.4米，花粉扩散距离的平均值为22.6米。两种扩散模式均以短距离扩散占比最高；长距离扩散在花粉传播中更为常见，但在种子传播中也时有发生。单株树木的繁殖成功率存在显著偏态分布：仅41%的成年个体产生了后代，绝大多数个体未参与繁殖。在参与本研究幼苗样本亲本贡献的个体中，80%的个体仅贡献了1-3个配子；仅20%的亲本个体贡献了4个及以上的配子。但这些数量极少的高繁殖力亲本，贡献了幼苗样本中51%的配子。本研究表明，看似均质的广袤栎林在遗传层面绝非均匀一致；相反，它们由规模极小的局域群落构成高度复杂的镶嵌体。这一现象抵消了长距离扩散的均质化效应，或可提升该物种的适应潜力。将这些动态机制纳入栎林的经营、保护与恢复工作中，有助于保护森林遗传多样性，并助力栎林应对环境变化。