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Ba Na Nature Reserve 1996
Papilionidae). Species inhabiting high-altitude or old-growth forests may also be underrepresented
due to the limited amount of collecting time spent in these habitats.
The number of species and individuals caught in each of the butterfly transects is shown in
Table 6.
Table 6. The total number of butterfly RTUs (S) and individuals (N) recorded from each transect
in 8 replicate surveys
RTUs (S) Individuals (N) α d
Transect 1 50 246 18.96 0.236
Transect 2 57 339 19.61 0.215
Transect 3 56 133 36.44 0.105
The degree of disturbance of the habitat decreased from BT1 to BT3. The degree of 'nativeness'
of vegetation decreased 3-1-2, with transect BT3 being the closest to a natural forest formation
for the area, and transect BT2 containing the highest proportion of alien species. It is perhaps
surprising therefore, that transect 2, where the vegetation is made up largely of a few, non-native
species, should have a highly diverse and abundant butterfly fauna. This runs counter to the
results of Spitzer et al (1987), who found that the number of butterfly species observed in
Vietnameses savanna and forest vegetation increased with the number of woody species present
in the habitat.
Although this result may be influenced by the high visibility of butterflies in the light shade of the
Eucalyptus, compared to the forest transect (where some species may have been confined to the
canopy, out of sight of the observers), it is in accordance with the results of studies in the Tam
Dao mountains, Vietnam (Spitzer et al, 1993), where disturbed habitats showed greater species
diversity than late-sucessional ones.The herb layer beneath the Eucalyptus stand may have
provided nectar plants to attract butterflies, and there were still open, sunny patches at the
plantation floor to attract heliophilous species.
However, when the diversity index, α, is calculated, diversity is greatest in the forest transect, 3.
Although the number of species found in this transect is fairly similar to those in other transects,
the diversity index is higher because each species was seen in lower numbers. Hence the index of
dominance d is considerably lower for transect 3 than 1 or 2. It is possible that, had BT3 been
subject to greater replications than the other transects, increasing the number of individuals (N)
observed, the number of species (S) may have been greater than that for the other transects.
The butterfly faunas recorded in the different habitat areas also showed distinct differences.
Figures 5 and 6 show the relative importance of each butterfly family in each transect, in terms of
the proportion of the total number of species and the total number of individuals.
Frontier- Vietnam Environment Research Report 7 21