Geoscience Reference
In-Depth Information
Indonesia. East Malesian includes the area east of Wallace's Line: Sulawesi, Lom-
bok, New Guinea, the tropical islands of Melanesia, and northeastern Australia.
Seasonal forests, often called monsoonal forests in this region, border tropical
rainforests. This boundary is largely determined by length and severity of the dry
season as it relates to soil moisture availability. Several types of seasonal forests
exist within the Asian-Pacific region. They include moist deciduous forests, dry de-
ciduous forests, and mixed deciduous forests. The region also contains dry ever-
green forest and dry thorn forest, which are all considered part of the Tropical
Seasonal Forest Biome. Different forest types vary in terms of forest structure and
dominant plant species.
Forest Types and Structure
Tropical moist deciduous forests are the wettest of the seasonal forests found in this
region. Rainfall averages 40-50 in (1,000-1,800 mm) or more annually, with a dis-
tinct dry season. Eighty percent of the total precipitation falls during the summer,
and a distinct dry season of four to six months occurs during the winter months.
The moist deciduous forest can have a closed or open canopy. Taller trees reach
heights of 33-130 ft (10-40 m), significantly smaller than those of the tropical rain-
forests (see Figure 5.19). In the lowland forests, climbing vines and lianas are less
abundant. The understory contains many different palms as well as smaller trees.
As elevation rises to 655-1,300 ft (200-400 m), vines and lianas become more com-
mon. In India, Thailand, and Myanmar teak (Verbenaceae) and sal trees (Diptero-
carpaceae) dominate on the less fertile soils, while trees in the legume family
(Caesalipiniacea subfamily) dominate on more fertile soils.
Mixed deciduous forests are found primarily in the northwest of Thailand and
into Myanmar and India. The structure of the mixed deciduous forest is complex
Figure 5.19 Forest structure in monsoon forest.
(Illustration by Jeff Dixon.)
