Human effects on long-distance wind dispersal and colonization by grassland plants

Human effects on plant colonization capacity have not been studied mechanistically because a crucial component of colonization capacity, long-distance seed dispersal, could not be quantified. Now, development of mechanistic models has progressed sufficiently to estimate long-distance seed dispersal by wind. We used a recently developed mechanistic dispersal model to quantify seed dispersal by wind in grasslands for three important human effects on natural systems: habitat fragmentation, eutrophication, and an increase in extreme wind velocity events due to climate change. We combined the dispersal data with data on seed production and germination ability to estimate effects on colonization capacity. Habitat fragmentation decreases the number and size of populations. This does not affect the populations' seed dispersal ability, but it reduces the number and germinability of produced seeds, and hence the colonization capacity. Site eutrophication strongly reduces seed dispersal distances, but in some species it also increases seed production and germinability. Thus, long-distance colonization decreases, but short-distance colonization may increase. Wind velocity is the key determinant of dispersal distances. An increase in extreme winds increases long-distance dispersal and long-distance colonization capacity. However, increases in extreme winds predicted for climate change scenarios are not sufficient to compensate the reductions in long-distance colonization due to habitat fragmentation or eutrophication.