Collaborative Research: Long Distance Dispersal of Tree Seeds by Wind: Underlying Mechanisms, Mathematical Prediction and Field Quantification

我们景观中的森林正越来越多地成为城市、郊区或农业用地的“海洋”中的孤立“岛屿”。为了让它们的种群在这样的景观中生存下来，树木必须将种子从一个岛屿散布到另一个岛屿。许多树利用风来散播种子。在强风中，特别是在崎岖的森林树冠上方或森林边缘附近，会形成三维的“漩涡”，有时风会向上吹。如果风的上升速度大于种子的下落速度，种子可以向上而不是向下。它甚至可能会遇到大的上升气流，比如暖空气上升的地方，或者山丘、森林边缘或大型建筑使风转向的地方。这样的上升气流可以将种子带到大气中，在那里它会遇到更快的风。或者，上升气流本身可以移动数英里，就像在雷雨中一样，然后让种子落在地面上。这个项目是生物学家和大气科学家之间的合作，目的是确定种子进入这些远距离传播模式的频率。这将需要测量种子从树上脱落之前的风力有多大，种子在静止空气中落下的速度有多慢，以及不同环境下风速的变化。最后，它将对风是否能将种子带到森林岛屿之间的距离进行实验测试。我们将对美国东北部18种散布在风中的树种的上升气流对种子传播的重要性和远距离传播的频率进行比较。这些信息对于了解森林物种的动态，以及在人类日益破坏景观的情况下维持森林物种至关重要。

Forests in our landscape are increasingly becoming isolated "islands" in a "sea" of urban, suburban, or agricultural land. For their populations to persist in such a landscape, trees must disperse their seeds from one island to the next. Many trees use the wind to disperse their seeds. In strong winds, especially over a rugged forest canopy or near the edge of a forest, three-dimensional "whirlpools" form with winds that sometimes blow upwards. If the upward velocity of the wind is greater than the rate of fall of the seed, the seed can go up rather than down. It may even get caught in a large updraft, such as happens where warm air rises, or where winds are deflected by a hill, a forest edge, or a large building. Such updrafts can take a seed high into the atmosphere, where it encounters faster winds. Or the updraft itself can move for miles, as it does in a thunderstorm, before letting the seed settle to ground. This project is a collaboration between biologists and atmospheric scientists to determine how often seeds go into these long-distance modes of dispersal. This will require measuring how strong the wind must be before seeds break loose from the tree, how slowly seeds fall in still air, and how the upward velocity of wind changes in different settings. Finally it will test experimentally whether winds can carry seeds as far as the distance between forest islands. The importance of updrafts for seed dispersal and the frequency of long-distance dispersal will be compared for 18 wind-dispersed tree species of the northeastern United States. Such information is vital for understanding the dynamics of forest species, and for maintaining them as humans increasingly fragment the landscape.