Data from: Costs and benefits of non-random seed release for long distance dispersal in wind-dispersed plant species

The dispersal ability of plants is a major factor driving ecological responses to global change. In wind-dispersed plant species, non-random seed release in relation to wind speeds has been identified as a major determinant of dispersal distances. However, little information is available about the costs and benefits of non-random abscission and the consequences of timing for dispersal distances.
We asked: 1) To what extent is non-random abscission able to promote long-distance dispersal and what is the effect of potentially increased pre-dispersal risk costs? 2) Which meteorological factors and respective timescales are important for maximizing dispersal? These questions were addressed by combining a mechanistic modelling approach and field data collection for herbaceous wind-dispersed species.
Model optimization with a dynamic dispersal approach using measured hourly wind speed showed that plants can increase long-distance dispersal by developing a hard wind speed threshold below which no seeds are released. At the same time, increased risk costs limit the possibilities for dispersal distance gain and reduce the optimum level of the wind speed threshold, in our case (under representative Dutch meteorological conditions) to a threshold of 5-6 m s-1. The frequency and predictability (auto-correlation in time) of pre-dispersal seed-loss had a major impact on optimal non-random abscission functions and resulting dispersal distances.
We observed a similar, but more gradual, bias towards higher wind speeds in six out of seven wind-dispersed species under natural conditions. This confirmed that non-random abscission exists in many species and that, under local Dutch meteorological conditions, abscission was biased towards winds exceeding 5-6 m s-1.
We conclude that timing of seed release can vastly enhance dispersal distances in wind-dispersed species, but increased risk costs may greatly limit the benefits of selecting wind conditions for long-distance dispersal, leading to moderate seed abscission thresholds, depending on local meteorological conditions and disturbances.

植物的扩散能力是驱动生态系统响应全球变化的核心驱动因子之一。对于风传播植物类群而言，与风速相关的非随机种子释放已被证实是决定其扩散距离的关键因素。然而，目前关于非随机种子脱落（non-random abscission）的成本与收益，以及脱落时机对扩散距离的影响，相关研究信息仍较为匮乏。

本研究提出两项核心科学问题：其一，非随机种子脱落能够在多大程度上促进长距离扩散？扩散前风险成本的潜在提升会产生何种效应？其二，哪些气象因子及其对应的时间尺度对最大化扩散距离至关重要？为解答上述问题，我们结合机理建模方法（mechanistic modelling approach）与野外数据采集，针对草本风传播物种开展了相关研究。

基于实测小时风速数据的动态扩散方法（dynamic dispersal approach）开展模型优化后发现，植物可通过设定严格的风速阈值（低于该阈值则不释放种子）来提升长距离扩散的概率。与此同时，扩散前风险成本的增加会限制扩散距离的提升空间，并降低最优风速阈值的水平；在本研究采用的荷兰代表性气象条件下，该最优阈值为5~6 m·s⁻¹。扩散前种子损失的发生频率与可预测性（时间自相关性，auto-correlation），对最优非随机种子脱落函数及最终扩散距离均具有显著影响。

我们在自然条件下对7种风传播物种中的6种进行观测，发现其种子脱落同样存在向高风速偏移的趋势，且该趋势更为平缓。这一结果证实，非随机种子脱落现象广泛存在于多个物种中；在荷兰当地气象条件下，种子脱落确实偏向于风速超过5~6 m·s⁻¹的情境。

综上，种子释放的时机能够大幅提升风传播植物的扩散距离，但扩散前风险成本的增加会显著限制通过选择有利风况实现长距离扩散的收益，最终形成适度的种子脱落阈值——该阈值的具体水平取决于当地气象条件与外界干扰。