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Official Magazine of the Nature Society (Singapore)
 
Bukit Timah Nature Reserve
a fragmented forest
surrounded by development
Photo by Ayesha Ecelawn
Is Our Oldest Forest Dying?
Part 1 | Part 2

Questions Galore... But no Ready Answers
So what questions could I answer after all this data was collected? One thought in all our minds was whether or not the forest at Bukit Timah will continue maintaining its high diversity.

One way to find out is to look at the composition of the new trees being recruited. We asked whether some species had become "too common" and whether they were reproducing at a higher rate than other species.

Our most common species was Santiria apiculata (Burseraceae) with 940 stems (7% of all the trees in the plot). Its rate of recruitment, however, was no higher than the average for the plot. Nor is its current dominance unusually high if compared to dipterocarp forests in Malaysia. Similarly, other species that were highly abundant did not show an excessive rate of recruitment. The diversity of new recruits was actually quite good. There were 885 new trees in the new 1 cm class and these represented 156 species. The plot itself had 321 species of trees.

Family
No. of stems (trees)
Percentage
Top ten families by stem density
One can look at forest composition either by stem count (no. of trees) or by basal area (how much area or "space" a tree is occupying). Obviously the really large seraya trees Shorea curtisii dominate the basal area, but Santiria apiculata (Burseraceae) was far more numerous.
Burseraceae
Euphorbiaceae
Moraceae
Ebenaceae
Clusiaceae
Dipterocarpaceae
Myrtaceae
Anacardiaceae
Rubiaceae
Ulmaceae
1940
1341
1019
819
655
641
574
528
468
454
14.76
10.21
7.75
6.23
4.98
4.88
4.37
4.02
3.56
3.46

Santiria apiculata
Photo by Shawn Lum
Trees that depend on animals to disperse
may be reproducing at a lower rate than others

Another question we tried to address was the vulnerability of tree species that need animals for dispersal. The fruit of trees in the nutmeg family, Myristicaceae, for example, are eaten and dispersed by hornbills. Except for the poor lost soul wandering in the Botanic Gardens area, the hornbill population in Singapore has vanished (for a correction on this statement). What of the trees that depend on them for dispersal. How critical were the hornbills for successful seed germination? This a question that cannot be easily answered and others will continue to work on it.

However, our data was able to show that overall, the tree species in the plot that depend on biotic dispersal (as opposed to wind, etc.) were recruiting at a lower rate than abiotically dispersed seeds, and that Myristicaceae had a particularly low recruitment rate. The plot covers only 2 hectares of Bukit Timah so the results can only be extrapolated with caution. However, it is one of the only sources of detailed information such as this, so is invaluable. As we obtain longer term data through repeat inventories in the future, many more answers should become available.



Map of Shorea curtisii

Seraya
A dipterocarp,
it can attain an
awe-inspiring height
Photo by Shawn Lum
Using our census data, we were able to produce maps like this one for each of the species in the plot. Detail such as this shows up patterns one may never discover just by walking around in the forest. All the young seraya (small dots) are actually growing slightly downhill and in the eastern part of the plot rather than near the larger trees where one might initially look for them.

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