Abstract:
A 1-ha secondary forest plot was established for studing species diversity,
species distribution and successional change at Mo Singto, Khao Yai National Park.
The forest started regenerating about 30 years ago from an old field disturbed by fire.
The secondary forest plot is adjacent to primary forest in the Mo Singto Forest
Dynamics Plot (FDP). Both primary and secondary forest plots have been surveyed in
20x20 m2 quadrats and all trees ≥1 cm dbh (diameter at breast high = 1.3 m) have been
censused. In the 1-ha secondary forest plot there were 9,382 individuals of 76 species,
compared with 4,695 individuals of 153 species found in the adjacent 1-ha area of the
primary forest. The most abundant species were Eurya nitida (63.8% of the total),
Schima wallichii (12.9%), Machilus odoratissima (7.3%), Symplocos cochinchinensis
(4.4%), and Aquilaria crassna (1.6%). The species composition and the distribution
patterns were different in the 2 forest types. Most species in secondary forest had a
random pattern, most species in the primary forest were clumped. In the secondary
forest, smaller trees (<10 cm dbh) tended to be more clumped than larger trees. Seed
dispersal mechanisms classified as: by animals, by wind, and by ballistics. In
secondary forest, 78% of species were dispersed by animal, 14% by wind and 8% by
ballistics. In primary forest, 88% of species were dispersed by animal, 6% by wind
and 4% by ballistics. There are differences in dispersal mechanism between primary
and secondary forest area. The numbers of individuals in the smaller size classes show
the regeneration ability of species. Of the 76 species occurring in the secondary forest,
18 were significantly more abundant in the secondary forest plot and 16 were
significantly more abundant in the primary forest. Soil samples were collected along
transects from primary to secondary forest and analyzed for texture, humidity, nitrate
nitrogen and ammonium nitrate. There were no significant differences in these factors
and all samples are characterized as sandy loam. This study will help selecting species
for planting in degraded areas to increase succession process for mature forest
development.