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Biodiversity and Local Perceptions |
7.3. Plant biodiversity
Tree species (dbh ≥10 cm) among 39 families and non-tree species among 80
families were inventoried. The most common families among non-trees were
Cyperaceae and Poaceae, both of which were present in 10 of the 11 plots. The
most common families among trees and non-trees combined were Rubiaceae and
Euphorbiaceae (each found in 9 plots) and Fabaceae (8). Among trees the most
common families were Euphorbiaceae and Moraceae (5) followed by Lauraceae,
Myrtaceae and Rubiaceae (4).
Twenty-eight percent of identified families and 84% of all plant species
were singletons, present in only one plot, which indicates the high diversity of
vegetation and large differences among land types. This view is also supported by
the data from non-tree species alone, in which case 68 of the total of 292 species
(identified and unidentified lumped together) were present in only one subplot
(out of 110 subplots), 38 in two subplots and 258 species (88%) were present
in only one land type. Only a few true generalists were recorded in many land
types. The most common and abundant non-trees were the herbs Centella asiatica
(Apiaceae), present in 34 subplots and four land types, Catimbium breviligulatum
(Zingiberaceae) in 33 subplots in four land types, and Curculigo cf. capitulata
(Hypoxidaceae) in 10 subplots and four land types. The next most common ones
were Hypolytrum nemorum (Cyperaceae) (23, 4), Schizostachyum cf. gracile
(Poaceae) (23, 2), Paspalum conjugatum (Poaceae) (21, 3) and Cleome viscosa
(Capparaceae) (19, 1). Nevertheless only a few species were shared between
different land types.
Secondary forests stand mainly on steep slopes and consist of diverse
tree species (from 20 to 30 tree species per plot, tree richness index from 0.81
to 0.91), often with fairly open canopy and dense understorey. Basal area in
secondary forests varied from 11 to 17 m 2 ha -1 . Relative dominance of a species
is commonly expressed as percentage of the total basal area. Based on this index
one more dominating tree species in secondary forests was identified (Figure 18).
Barringtonia macrostachya (Lecythidaceae) was recorded in all secondary forest
plots with its relative dominance always being close to 35%. Its relative abundance
(percentage of the total number of individuals per plot) varied from 15% to 43%.
Other species with relative large basal areas were Cinnamomum cf. burmannii
(Lauraceae) (21% present in one plot) and Aporosa tetrapleura (Euphorbiaceae)
(relative dominance from 2% to 8% in three plots, present in both secondary and
primary forest). In secondary forests 55 tree species (132 individuals) out of the
total of 70 species were present with a single individual, indicating high overall
diversity of the forests and the need for larger sample size for trees if more rigorous
information on them is needed.
Planted and managed forests are very common and promoted by the
government, thus many bare hills have recently been converted into mixed fast
wood plantations of Acacia mangium, Acacia auriculiformis and Acacia siamensis
(Plot 5) or rubber (Hevea brasiliensis) plantations (Plot 1). Since for example A.
mangium reaches harvest age in a mere 6 to 8 years after planting, the landscape
has changed fast. Planting Acacia has also been supported by its catalyzing effect