|Abstract or Summary
- Tropical island ecosystems have proven to be inordinately vulnerable to
invasions by exotic plants and animals. Today these islands only contain small
remnant populations of the original flora and fauna, and these populations are facing
increasing pressure from invasive plants. This paper attempts to answer four
important questions whose solutions will help explain the phenomena of greater
invadeability on islands. These questions are 1) Why is the vegetation on tropical
islands so vulnerable to invasions? 2) What are the attributes of the woody plants
which invade islands? 3) What are the impacts of the invasions on the natural plant
communities? 4) What are the methods of control and their costs and benefits?
Section two contains a management plan for the control of the invasive species
Psidium cattleianum in Ranomafana National Park, Madagascar.
The vulnerability to invasion of vegetation on tropical islands was attributed
to evolution with different selective forces, the history of human disturbance on
islands, disharmony, and an inherent vulnerability of island flora.
The attributes of invasive woody plants which promoted invasions was explained in terms of safe site occupancy, demography, physiology, dispersal
characteristics, and seed and fruit characteristics.
The impacts of invasive plants on tropical islands can cause long-term changes
in ecosystems. These changes include; a change in community structure, a change
in fire distribution patterns, a change in nutrient status, a change in the soil-water
regimes and hydrological processes, and changes in diversity.
Ecological control methods in natural systems were examined as were their
costs and benefits. The objectives of the control operation must be clearly
understood before an integrated weed control program can be implemented.
Mechanical, chemical, biological and legislative control options are testable, and such
tests are recommended. The target plant should be understood on both an individual
and population level. The economic, sociological and ecological implications of the
control operations must be understood before an operation can begin. Often two or
more control strategies may be used simultaneously to optimize the effectiveness of
control. Once the desired level of control is achieved, native species for the site must
be established to insure a maximum degree of ecological restoration.
The objectives of the management plan in Ranomafana National Park,
Madagascar are to control and greatly reduce the extent and dominance of
strawberry guava within the boundaries of the park, and to occupy the current guava
infestation sites with native species. The management plan will be implemented in
two phases. The first phase will be for research and development, during which the
baseline information regarding extent of infestation, control methods, and nursery
and outplanting technology will be developed. The second phase will be the integrated management program, in which the control measures and the restoration
efforts will be accomplished. An estimated minimum budget for an eight-year
management plan without biological control is $214,740.