Accurate predictions of seed dispersal kernels are crucial for understanding both vegetation communities and landscape dynamics. The influences of many factors, including the physical properties of seeds, the time-averaged wind speed and the wind turbulence, on seed dispersal have been studied. However, the influence of local wind speed reduction around a single shrub element (e.g. a small patch of scrub) on seed dispersal is still not well understood. Here, the spatial distribution of the wind intensity (represented by the wind friction speed u*) around a single shrub element is described, with an emphasis on the variation in the streamwise direction, and assuming that the time-averaged lateral and vertical speeds are equal to zero. The trajectories of the seeds were numerically simulated using a Lagrangian stochastic model that includes the effects of wind turbulence and particle inertia. The patterns of seed deposition with and without the effect of local wind reduction were compared. The variation in seed deposition with changing wind intensity, release height and shrub porosity were also simulated. The simulation results revealed that the local wind reduction increased seed deposition in nearby regions and therefore decreased seed deposition in the regions farther away. Local wind reduction had a greater impact on short-distance dispersal than on long-distance dispersal. Moreover, the dispersal in the circumferential direction decreased once the motion of a seed moving in the streamwise direction was reduced due to the local wind reduction. As the wind intensity and release height increased, the effect of local wind reduction on seed dispersal weakened. Seed dispersal was both wider and farther as the shrub porosity increased. These results may help explain the disagreement between the mechanistic models and the fitting curves in real cases. In addition, the results of this study may improve the currently used mechanistic models by either increasing their flexibility in case studies or by helping explain the variations in the observed distributions.

中文翻译：

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局部减风区对植被稀疏土地上单一灌木元素种子传播的影响

种子传播内核的准确预测对于了解植被群落和景观动态至关重要。研究了种子的物理性质、时间平均风速和风湍流等多种因素对种子传播的影响。然而，围绕单个灌木元素（例如一小块灌木）的局部风速降低对种子传播的影响仍然没有得到很好的理解。这里，描述了单个灌木元素周围的风强度（由风摩擦速度 u* 表示）的空间分布，重点是流向的变化，并假设时间平均横向和垂直速度为等于零。使用拉格朗日随机模型对种子的轨迹进行数值模拟，该模型包括风湍流和粒子惯性的影响。比较了有和没有局部减风影响的种子沉积模式。还模拟了种子沉积随风强、释放高度和灌木孔隙度的变化。模拟结果表明，局部风的减少增加了附近地区的种子沉积，因此减少了更远地区的种子沉积。局部风力减弱对短距离扩散的影响大于对远距离扩散的影响。此外，由于局部风的减少，一旦种子沿流向运动的运动减少，则沿圆周方向的扩散减少。随着风强和释放高度的增加，局部减风对种子传播的影响减弱。随着灌木孔隙度的增加，种子传播的范围更广、更远。这些结果可能有助于解释机械模型与实际案例中的拟合曲线之间的分歧。此外，这项研究的结果可以通过增加案例研究的灵活性或帮助解释观察到的分布的变化来改进当前使用的机械模型。