The proposed Parc Regional de Belomotse - Frontier-publications ...

families Euphorbiaceae and Fabaceae had the most species (14 each), followed by
Malvaceae (7) and Burseraceae (6). Two of the families present, Physenaceae and
Sphaerosepalaceae, are endemic to Madagascar.
A total of sixty tree and large shrub genera were identified in the spiny forests, twelve
(20%) of which are endemic (see table 3). The total number of species that were
collected was 118, with 86 being identified and named to the species level. As with
the gallery forest species, endemism at the species level is not included.
Throughout all surveyed areas of spiny forest, there were few large (DBH > 25 cm)
tree species. The upper size ranges were dominated by Antsilodendron sp.,
Commiphora spp. and Operculicarya decaryi. These species formed an open, low
canopy 3-10 m in height in undisturbed areas. The canopy height depended on the
gradient and substrate of the area. The tree species that were dominant through the
lower size ranges were Croton sp. 3, Grewia grevia and Diospyros latispatula.
4.4 Discussion
The most significant achievement of the botanical survey was the production of a
preliminary species list for the two main natural habitats within the proposed regional
park. Few inventory studies have been undertaken in the region, so this species list
can be used for comparative studies and monitoring when further studies have been
completed in other areas. At present, the analyses of survey data are awaiting the
completion of comparative studies, in order to allow comparisons to be made and
specific regional habitats to be identified. Therefore, this discussion will focus on
forest structure, dominant species, resource use and threats to the spiny and gallery
forests.
4.4.1 Dominant species and forest structure
The two most dominant tree and shrub species within each size class and habitat are
shown in Table 4. The data show clearly that there are very few dominant habitatgeneralist
species. By that, it is meant that the dominant species within the spiny
forests are almost entirely absent in the gallery forests, and vice versa. This seems to
indicate that, within the region, habitats that may be only metres apart are clearly very
different in terms of plant dominance and forest structure. It also indicates the habitatspecific
diversity within the spiny and gallery forests of southwest Madagascar.
The results in Table 4 also show that in gallery forest, a small number of species are
dominant, but they are dominant through more than one size class. For example,
Celtis bifida was one of the two most dominant plant species within every size class.
This leads to the ground layer, shrub layer and canopy layer of gallery forest being
dominated by a small number of species.
In contrast, the spiny forests show a much greater diversity of dominant species
between the different size classes. None of the plant species that are dominant in the
lower size classes are even found in the upper size classes. This reflects the diversity
of species that are found in the ground layer, shrub layer and canopy layer, and shows
the level of niche-specificity that spiny forest plant species exhibit.
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