Long-distance dispersal of tree seeds by wind. Horn, Henry S.; Nathan, R.A.N.; Kaplan, Sarah R..
Some mechanisms that promote long-distance dispersal of tree seeds by wind are explored. Winged seeds must be lifted above the canopy by updrafts to have a chance of further dispersal in high velocity horizontal winds aloft or in landscape-scale convection cells. Shear-induced turbulent eddies of a scale up to one-third of canopy height provide a lifting mechanism. Preliminary data suggest that all seeds of a given species may be viable candidates for uplift and long-distance dispersal, despite the evidence that slow-falling seeds are dispersed farther under any given wind conditions. Turbulence is argued more often and more extensively to advance long-distance dispersal than to retard it. Seeds may take advantage of 'Bernoulli sailing' to move with faster than average winds. Elasticity of branches and trees may play a role in regulating the release of seeds into unusually favorable winds. Dispersal is at least biphasic, and the study of long-distance dispersal calls for mixed models and mixed methods of gathering data.
Towards a theoretical basis for ecosystem conservation. Rozdilsky, Ian Douglas; Chave, Jerome; Levin, Simon Asagr; Tilman, David.
Humans have altered the environment so severely that extinction events are now occurring at rates unprecedented in modern history. In order to slow this trend, conservation actions must be taken to protect biodiversity, beyond just saving flagship species. Some governmental and conservation organizations have responded by committing to ecosystem conservation but, as yet, there is no coherent strategy for how this can be carried out. This report introduces many of the theoretical aspects that will need to be considered for the development of a coherent ecosystem conservation policy. The approach includes analyzing a hierarchy of interaction-based local coexistence mechanisms within a regional and historical context. This approach points toward the need for prioritizing sensitive habitats using local interaction models; considering the effects of historical exploitation mechanisms, which are now often missing; and evaluating regional diversity influences further to identify circumstances where system-wide habitat improvements deserve more emphasis.