Geoscience Reference
In-Depth Information
area did not have the moist tropical forest it has today. As the Australian Plate
moved equatorward, climate changed. It became warmer and wetter, and the area
developed unique plant and animal communities, the precursors of what is found
there today. As the Australian region continued its northward movement, the plate
collided with the Asian continent (30-20 mya). This allowed for the dispersal of
Asian species into the region. Some differences in species between Asian and Aus-
tralian flora and fauna still exist. Wallace's Line between Borneo (Kalimantan)
and Sulawesi (Celebes) and Bali and Lombok farther south define the end of the
Sunda Shelf, a shallow extension of the Asian continental plate underlying most of
Indonesia (see Figure 3.15). The deep trench at the end of the shelf is a significant
barrier to species dispersal, keeping species (particularly mammals) distinctive and
separate.
Climate
The climate throughout the Asian-Pacific rainforests is tropical. All seasons are hot
and humid, and temperature varies little. Monsoonal winds control much of the
climate in this region and create four seasons. A monsoon is a prevailing wind that
lasts for several months and then reverses its direction. The southwest monsoonal
season occurs from May to September and brings heavy rainfall and strong winds
to the rainforests of India and Bangladesh. The southwest monsoon season brings
less severe weather to southern Asia and Australasia. From November to March
comes the winter, northeast monsoon season. Strong north and northeast winds
originating from cold, northern Asia mix with tropical winds and bring severe
weather, including heavy rainfall and typhoons, to Southeast Asia and Australasia.
These winds are lighter along the Indian continent and produce less rain there. The
two other seasons are intermonsoon seasons. During these times, the climate
remains hot and humid, but winds and rainfall, although continuous, are lighter
than in the monsoonal seasons.
Annual rainfall in the Asian-Pacific rainforest is more than 80 in (2,000 mm). It
is distributed throughout the year. In many areas, rainfall can exceed 120 in (3,000
mm), particularly in northwestern Borneo and New Guinea. As noted above, rain-
fall decreases during intermonsoon seasons, which can last one to four months in
some areas. In areas such as New Guinea, no regular dry season develops and
monsoonal winds are less significant.
Temperatures average around 87
F (31
C) during the day, with nighttime
lows around 72
F (22
C). Average monthly temperatures vary by less than 4
F
(2
C), but, as in other rainforests, a single day's temperature can vary as much as
14
C). Average humidity is 70-80 percent throughout the year.
Changes in the monsoonal cycle can lead to prolonged drought, and periods of
hot, dry weather can create an environment vulnerable to fire. In the past, fires
have been widespread and catastrophic to the rainforest. El Nino events, which
F(8
