What is typical to the forests of Guyana in comparison with other Neotropical forests?
Guyana is largely covered by forests (Figure 4) and many of these are still intact. This fact by itself is significant in a time that most of the world's tropical rainforests are under pressure. However, intactness is only one criterion for designing a system of protected areas. Another criterion would be to protect species and ecosystems, which are typically Guyanese. A wider perspective is required to place Guyana in a Neotropical context.
To this end the forest composition of 258 plots of 1 ha scattered over the Neotropics was examined (28). The first remarkable conclusion is that Guyana's forests, while species-rich compared to temperate forests, are poor[2] compared to forests in Western and Central Amazonia (Figure 2). Tree a-diversity generally seems to drop when moving from west to east through the Amazon basin, with the poorest plots in the peripheral areas in the North, far South and East.
Figure 2. Location of 258 amazonian plots used in the analysis of tree a-diversity. Dot size indicates the value of Fisher's a (in case of overlap only the highest will be visible). Grey-scales indicate interpolated values of Fisher's a (with interdistance weighting up to 500 km).
Several families are better represented in Eastern Amazonia and the Guianas than in Western Amazonia, and vice versa. Chrysobalanaceae (Kauta's etc.), Lecythidaceae (Kakaralli's), and Leguminosae are examples of such families (28). Palms are a striking example of the reverse pattern. Guyana is unique in its high abundance of Caesalpiniaceae, a subfamily of the Leguminosae (Figure 3 (29)). Well-known members of this family are the Wallaba's (Eperua spp.) and Mora's (Mora spp.). Their high abundance frequently leads to monodominance - forest communities strongly dominated by a single species.
Figure 3. Regional dominance of Caesalpiniaceae expressed as the percentage of individuals in large-scale inventories in the Guiana Shield. The dot size indicates dominance and ranges from 9% (smallest) to 45% (largest).
The total flora of Guyana comprises almost 6,000 species (1), compared to
4,100 in Surinam and 4,400 in French Guiana. While this may appear much less
than the 55,000 species found in Brazil, this is mainly an effect of the much
smaller area of these countries (21). It is not well known what percentage of
the flora is confined to Guyana (endemics). A preliminary list by C.A. Persaud
included 284 endemics or 5% of the total flora. However, further exploration may
add new species to this list and remove others. See also below for a further
discussion of endemism.
Guyana's forests are:
[note 2] Poor when expressed on the scale of 1-ha plots. The total number of species in the entire country depends also on other factors, such as geographic variation.