Data from: Stochastic and deterministic effects on interactions between canopy and recruiting species in forest communities

1. Interactions between established (canopy) and recruiting individuals (recruits) are pervasive in plant communities. Studies on recruitment in forests have mainly focused on negative density-dependent conspecific interactions, while the outcomes of heterospecific canopy-recruit interactions have received much less attention and are generally assumed to be driven by stochastic processes. 2. Herein, we explore the relative influence of stochastic (abundance) and deterministic (species identity and phylogenetic distance) effects on the frequency of canopy-recruit interactions, and characterise the interactions in terms of their spatial consistency and effect on recruitment (depressing, neutral or enhancing). 3. In 12 plots (50  50 m) of mixed pine-oak forests in Southern Spain we identified all saplings recruiting beneath 56 shrub and tree species, and in open areas not covered by woody plants. We used generalised linear mixed models to investigate the influence of stochastic and deterministic processes on the frequency of canopy-recruit interactions, on their spatial consistency and their effects on recruitment, and applied neutral null models to evaluate the spatial consistency in the occurrence of interactions across plots. 4. Deterministic and stochastic interactions were equally common emphasizing the prevalence of non-neutral effects. Among the realized interactions, 36.8% enhanced recruitment, 49.05% were neutral, and 14.1% depressed recruitment. Many potential interactions (42.08%) were not observed in any study sites, presumably due to the scarcity of the interacting species. Moreover, the probability that two species formed a canopy-recruit interaction, the frequency of their interaction, and the probability that the interaction had an enhancing effect on recruitment, all increased with the phylogenetic distance between the interacting species. However, the prevalence of these effects depended on the recruitment environment (heterospecific, conspecific or open). Recruitment-enhancing interactions between heterospecifics were more consistently realized in different sites than neutral or depressing interactions. 5. The establishment of canopy-recruit interactions (which species recruits beneath which others, and how often) is not simply determined by stochastic events. Indeed, due to their prevalence we argue that deterministic canopy-recruit interactions are important drivers of plant community dynamics.

1. 冠层（canopy）成体个体与更新幼苗（recruits）之间的相互作用在植物群落中普遍存在。针对森林更新的研究多聚焦于负密度依赖的同种相互作用，而异种冠层-幼苗相互作用的相关结果则受到的关注甚少，且通常被认为由随机过程驱动。
2. 本研究探讨了随机因素（种群丰度）与确定性因素（物种身份及系统发育距离）对冠层-幼苗相互作用发生频率的相对影响，并从空间一致性及其对幼苗更新的作用（抑制、中性或促进）角度对该类相互作用进行了表征。
3. 我们在西班牙南部12块50米×50米的松栎混交林样地中，对56种灌木和乔木冠层下方以及无木本植物覆盖的开阔区域内的更新幼苗进行了全面鉴定。我们采用广义线性混合模型（generalised linear mixed models）探究随机与确定性过程对冠层-幼苗相互作用频率、空间一致性及其对更新作用的影响，并运用中性零模型（neutral null models）评估不同样地间相互作用发生的空间一致性。
4. 确定性相互作用与随机性相互作用的发生频率相当，凸显了非中性效应的普遍性。在已观测到的相互作用中，36.8%可促进幼苗更新，49.05%为中性相互作用，14.1%则会抑制更新。另有42.08%的潜在相互作用未在任何研究样地中被观测到，推测其原因在于相互作用物种的种群稀有性。此外，两个物种形成冠层-幼苗相互作用的概率、其相互作用的发生频率，以及该相互作用促进幼苗更新的概率，均随物种间系统发育距离的增加而升高。不过，此类效应的强弱取决于更新微环境（异种、同种或开阔区域）。异种间的更新促进相互作用在不同样地中的发生一致性高于中性或抑制性相互作用。
5. 冠层-幼苗相互作用的建立（即哪些物种在哪些物种冠层下更新，以及更新频率）并非仅由随机事件决定。事实上，鉴于确定性冠层-幼苗相互作用的普遍性，我们认为其是驱动植物群落动态的关键因素。