Southeast Environmental Research Program, Florida
International University
Center for Plant Conservation
PART II: THE FLORIDA NATIVE PLANT RESOURCE
D. Conclusion: factor interactions
For the most part, the discussion above has avoided attributing documented habitat and population declines to specific causes, primarily because of the multifactorial nature of the problems underlying plant population dynamics. The following example illustrates the point. In August, 1992 Hurricane Andrew passed over southern Dade County, as have countless previous hurricanes. Months after the storm, an outbreak of
Ips spp. beetles decimated the dominant slash pine (Pinus elliottii var. densa ) canopy.
Scientists attributed the severity of the outbreak to lowered water levels (see Altered hydrology, above) and/or structural changes in the pine forest associated with frequent
winter fires (see Altered disturbance regime, above). Because the pine rockland forests
of the Coastal Ridge had already been reduced in extent by more than 90% (see Habitat
loss, above), and because the remaining parcels were widely scattered within an urban
matrix (see Habitat fragmentation, above), there was little likelihood that slash pine
would be reestablished from natural seed sources outside the infested area. Further
more, exotic tree and grass populations that had invaded the pine forests prior to the
hurricane were relatively unaffected by the storm and the insect attack that followed
(see Non-indigenous plants, above). The presence of these introduced species thus presented a significant barrier to reestablishment of the pine canopy, without which a fire
regime critical to the many rockland herbs was impossible. One of these native herbs,
Zamia pumila, was once abundant in these forests but had been harvested commercially
as a starch source early in the century, becoming much less common today (see Over
exploitation, above). In the longer term, there is a strong likelihood that the low lying
rockland communities closest to the coast will be threatened by salt water intrusion
caused by sea level rise (see Global climate change, above). Superimposing the complex anthropogenic background recounted above on the complexities associated with
natural ecosystems -- climatic variability, species interdependencies, etc. -- one would
be hard pressed to attribute a simple cause to the decline of any pine rockland plant
population, despite the very considerable evidence of human involvement.
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