Prunus serotina unleashed: invader dominance after 70 years of forest development

Propagule pressure and disturbance have both been found to facilitate invasion. Therefore, knowledge on the history of introduction and disturbance is vital for understanding an invasion process, and research should focus on areas in which the invasive species has not been deliberately introduced or managed to study unconfounded colonization patterns. Comparing the outcome of such spontaneous colonization processes for different ecosystems might provide a useful framework for setting management priorities for invasive species that enter new, uninvaded areas. We focused on the 70-year spontaneous spread of the invasive tree species Prunus serotina in a pine forest in the Netherlands. To reconstruct the invasion pattern, we combined historical maps, tree ring analysis, spatially explicit tree inventory data, seed density data, and regeneration data for both native and non-native species. Prunus serotina was the only species that showed successful regeneration: the species was present throughout the forest in the tree, shrub, and herb layer. Native species were not able to outgrow the seedling stage. Our data demonstrate that P. serotina is a gap-dependent species with high seed production that builds up a seedling bank. We also compared the results of this study with a similar study on P. serotina colonization in a deciduous forest in Belgium, where P. serotina invasion was not successful. The sharp contrast between the outcomes of the two invasion processes shows the importance of studying an invasive species and the recipient ecosystem jointly and made us raise the hypothesis that herbivore pressure may facilitate P. serotina invasio

Delaying the Catastrophic Arrival of the Brown Tree Snake to Hawaii

This paper develops a two-stage model for the optimal management of a potential invasive species. The arrival of an invasive species is modeled as an irreversible event with an uncertain arrival time. The model is solved in two stages, beginning with the post-invasion stage. In this stage, we assume perfect certainty regarding population size and arrivals. The loss-minimizing paths of prevention and control are identified, resulting in a minimized present value penalty associated with the invasion. After calculating this penalty, we analyze the pre-invasion stage and solve for the level of prevention expenditures that will minimize expected total cost. For the case of the Brown Tree Snake potentially invading Hawaii, we find that under a regime of precommitment, pre-invasion expenditures on prevention should be approximately $3.2 million today, decreasing every year until invasion. However, if the planner is permitted to re-evaluate the threat following a non-event, prevention will be lower ($2.96 million a year) and constant until invasion. Once invasion occurs, optimal management requires lower annual expenditures on prevention ($3.1 million) but requires$1.6 million to be spent on control annually to keep the population at its steady state level.catastrophe, hazard function, invasive species, Brown Tree Snake, Boiga irregularis, prevention and control, Hawaii

ENVIRONMENTAL VARIABLES ASSOCIATED WITH INVASIVE GLOSSY BUCKTHORN (FRANGULA ALNUS MILL.) AND INDIRECT CONTROL STRATEGIES FOR FOREST MANAGERS

Glossy buckthorn (Frangula alnus Mill.) is one of the most prominent non-native invasive plant species affecting New England forests. It quickly invades a forest and can create a dense understory effectively altering the species composition and dynamics of that forest. To gain a better understanding of the environmental variables associated with glossy buckthorn density we sampled forests across New Hampshire with varying degrees of buckthorn invasion. The effect on tree regeneration was analyzed with measurements of height and abundance of glossy buckthorn and native regeneration. Glossy buckthorn was found to be at its highest densities in disturbed softwood forests that were historically old fields, specifically eastern white pine (Pinus strobus L.), with a thin organic layer and low herbaceous cover on drained loam and clay soils. The data show there is direct competition between glossy buckthorn and forest tree regeneration, although no relationship with regeneration shade tolerance was found. This information was used to create a prescription risk tree to aid forest managers in assessing the risk of buckthorn invasion and inhibition of tree regeneration associated with harvesting and suggests how to adapt their silvicultural prescriptions

The influence of vegetation structure and composition on invasibility by Pinus radiata in the Blue Mountains, NSW

The exotic tree species Pinus radiata D. Don (in the family Pinaceae) has successfully spread from commercial plantations into adjacent vegetation in southeastern Australia. Identifying factors facilitating spread will aid the control of current invasions and the prediction of future invasion events. The structure and composition of vegetation can have an important role in determining community resilience to invasion. Two dry eucalypt sclerophyll woodlands in the Blue Mountains west of Sydney known to be invaded by Pinus radiata were surveyed to investigate the influence of eucalypt presence, species diversity, species composition and vegetation cover on the extent and density of invasion. Relationships between community characteristics and the level of pine invasion were weak and variable. Pines were found growing in plots with 0–70% understorey cover and 5–90% ground cover, and in areas of both high and low eucalypt diversity and presence, illustrating the high invasion potential of Pinus radiata

Invasion percolation and global optimization

Invasion bond percolation (IBP) is mapped exactly into Prim's algorithm for finding the shortest spanning tree of a weighted random graph. Exploring this mapping, which is valid for arbitrary dimensions and lattices, we introduce a new IBP model that belongs to the same universality class as IBP and generates the minimal energy tree spanning the IBP cluster.Comment: 4 pages, 3 Postscript figures avaliable from [email protected], REVTE

Exponential growth of ponds in invasion percolation on regular trees

In invasion percolation, the edges of successively maximal weight (the outlets) divide the invasion cluster into a chain of ponds separated by outlets. On the regular tree, the ponds are shown to grow exponentially, with law of large numbers, central limit theorem and large deviation results. The tail asymptotics for a fixed pond are also studied and are shown to be related to the asymptotics of a critical percolation cluster, with a logarithmic correction