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

在我们的景观中，森林正日益成为城市、郊区或农业用地“海洋”中的孤立“岛屿”。为了让它们的种群在这样的环境中生存下去，树木必须将它们的种子从一个岛屿传播到另一个岛屿。许多树利用风来传播种子。在强风中，特别是在崎岖的森林树冠上或靠近森林边缘的地方，三维的“漩涡”会随着有时向上吹的风形成。如果风的上升速度大于种子的下降速度，种子就会上升而不是下降。它甚至可能被困在一个大的上升气流中，比如在暖空气上升的地方，或者在风被山丘、森林边缘或大型建筑物偏转的地方。这样的上升气流可以把种子带到大气层的高处，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，就像在雷暴中一样，然后让种子落地。这个项目是生物学家和大气科学家之间的合作，旨在确定种子进入这些长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有多大，种子在静止的空气中落下的速度有多慢，以及在不同的环境中向上的风速是如何变化的。最后，它将通过实验来测试风是否能把种子带到森林岛屿之间的距离。以美国东北部18种风散树种为研究对象，比较了上升气流对种子传播的重要性和长距离传播的频率。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保持它们至关重要。

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.