From field studies to models: How to predict the invasive spread of Juniperus bermudiana in Hawaii

Background/Question/Methods Few studies link the processes that mediate avian seed dispersal with its impacts on invasive plant distribution on a landscape level. My study (1) measures the seed dispersal effectiveness (i.e., quantity and quality of seed dispersal) of an invasive plant, Juniperus bermudiana (Bermuda Juniper), dependent on avian seed dispersal and (2) determines how these estimates can help predict the spread rate and distribution of an invasive plant on a landscape level. I have conducted tree watches, seed trap studies, bird point counts and vegetation surveys in the West Maui Mountains of Hawaii to measure the quantity and quality of avian seed dispersal on J. bermudiana; I have also conducted vegetation surveys to characterize J. bermudiana density and forest types for use in spatially-explicit simulation models. Results/Conclusions Field studies revealed Zosterops japonicus (Japanese White-Eye) to be the most effective seed disperser due to its high abundance and wide distribution in the study site. The spread rate and distribution of J. bermudiana in Hawaii is not likely to be limited by the abundance of seeds nor by the presence of effective seed dispersers (i.e., the quantity of seed dispersal). Instead, it is likely that the effectiveness of avian seed deposition (i.e., the quality of seed dispersal) has limited the spread rate and distribution of J. bermudiana. I have incorporated data from these behavioral studies and field experiments into a spatially explicit, individual based simulation model that aims to predict the spread rate and distribution of J. bermudiana on a landscape level. Preliminary work on this modeling approach provides data on the sensitivity of J. bermudiana spread and distribution to the specific stages of the avian seed dispersal process. Results of this study will inform restoration and conservation management of the study site and potentially other threatened Hawaiian forests where bird-dispersed invasive plants are present.