Understanding the large-scale pattern of exotic vine spread: Do power and telephone networks function as corridors aiding exotic vine invasion?

Background/Question/Methods

The spread of invasive plants specie has become a worldwide concern and among these, exotic vines stand out in part due to their ability to climb onto other structures and disperse into new areas. In this way, they can take advantage of fences, poles and telephone lines to overcome physical barriers (i.e. rivers, mountains), thus rapidly spreading and dominating a landscape. However, the role of such structures shaping and aiding the spread of vines has not been examined. One promising avenue to examine this pattern is through their representation as networks whereby patches of vines and dispersal among them are depicted as nodes and edges, respectively. We hypothesize a vine invasion network resembles that of a network made up by the areas vulnerable to past intentional introduction (i.e. pastures and croplands) and the network of power and telephone lines, which provide connectivity between these areas. To explore this hypothesis we centered on the Rio Grande de Arecibo watershed, located in the central area of the island of Puerto Rico, and followed a three-step approach. First, we mapped the vine cover in the area by running supervised classifications on IKONOS satellite images (1m resolution). Second, we created a vine invasion network and described its topology. In this network, vine patches of area ≥ 4m² were represented by nodes and linked by edges if they were ≤30m in proximity. Third, we compared the vine network topology with that of three different physical representing the possible scenarios explaining the invasion pattern observed. The simplest of the three networks is made only of the areas historically vulnerable to vine introduction, while the other two include possible pathways of dispersal such as the road network and the power and telephone lines network.

Results/Conclusions

Preliminary results from the mapping of vines show a heterogeneous pattern of exotic vine invasion with a 12.8% vine cover in an area of 300km² inside the watershed. These vines form dense patches that vary in size ranging from 2,000m² to 41,200m². Also, ground data from poles inside the watershed showed that 72% out of 179 poles were covered with vines and that in 40% of the cases these vines continue their spread along the electric and telephone lines, suggesting their role as pathways for vine spread. Finally, this use of networks to understand the spread of invasive vines can be applied successfully to other areas and provide practical information for management plans.