Roads have the potential to serve as dispersal corridors for invasion into pristine habitats for invasive exotic species. However, undisturbed habitats may also resist such invasion. Torpedograss (Panicum repens L.) is an aggressive invasive grass in many parts of the world and, although most problematic in lakes and ponds, frequently occurs in roadsides and in other disturbed habitats. We studied torpedograss dynamics along roadsides adjacent to upland habitats in south-central Florida to determine whether observed tiller population growth rates differed among roadside populations adjacent to different habitats. We also examined seasonal growth and persistence patterns of this invasive species in sand roads, quantifying torpedograss density, growth, and panicle production at 10 roadside sites every other month for 14 mo. Four populations were adjacent to disturbed habitats (pastures or disturbed Florida scrub) containing established populations of torpedograss, while six populations were adjacent to undisturbed Florida scrub lacking torpedograss. Population growth rates were negative in most roadsides neighboring undisturbed scrub, and positive when neighboring disturbed habitats. Tiller density, tiller height, and panicle production were all greatest in late summer, and tiller density increased with temperature and relative humidity. We observed no evidence of recruitment from seed. We never found any invasion of undisturbed Florida scrub, consistent with the hypothesis that undisturbed Florida scrub resists invasion. Results suggest that, in xeric habitats, land managers should give higher priority to restoring disturbed habitats or controlling expansion from disturbed habitat edges rather than to eradicating roadside populations of torpedograss.
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Vol. 81 • No. 3