Modelling wind and seed dispersal patterns to identify high threat willow population in Bogong High Plains

The invasion of Salix cinerea (grey sallow willow) is one of the major threats to Sphagnum bogs on the BHP. Sphagnum bogs is a threatened ecological community protected under the EPNC Act. The genus Salix is a Weed of National Significance (WONS) and S. cinerea being one of the few seed producing willows in Australia is highly invasive. Identifying the high threat locations of these willows is hence a top priority of the managers. The Salix cinerea seeds are dispersed mainly by wind but the inability to estimate this dispersal distance of these seeds makes it very hard to decide which areas of the established Salix cinerea population around the BHP pose high threat to the wetland ecosystems. Recent research has revealed that high threat seed source populations can be identified by improving our knowledge of the dispersal capability of the propogule. The literature suggests that the long distance dispersal of the seeds is mainly governed by the weather and topographical parameters of the region such as wind uplift, elevation and horizontal winds near ground. Thus, it was essential to identify the driving factors behind the dispersal of Salix cinerea on the BHP. In this project we have characterised the wind and seed dispersal patterns over the BHP region using a meso scale model (TAPM) by simulating the weather conditions from the synoptic data. As topographical variation is significant in the region of BHP, TAPM was used to model the weather patterns in the region at a smallest grid resolution of 500 m. The weather data was further analysed to study the effect of topography on the wind patterns. These weather simulations were further used to simulate various seed dispersal events all over the region with a certain set of predetermined parameters. We combined field measurements of seed production and information from literature to parameterise a seed dispersal regime which was used to run the above said seed simulations in the model to predict the seed dispersal patterns. The simulations were run for the month of November as the Salix cinerea have been known to seed during this month. Being a mechanistic model, TAPM's simulations were analysed for individual seed sources with respect to individual parameters to study a comprehensive pattern of seed dispersal in the region. This helped in identifying the key driving factors of the dispersal mechanism. It was found that weather patterns do affect the seed dispersal mechanism to a great extent and the dispersal kernel is almost always anisotropic as the prevailing winds drive the seeds along a specific direction. The dispersal pattern was found to be highly skewed with a long tail suggesting that most of the seeds were being deposited very close to the source and very few seeds were being carried to long distances on rare occasions