Geoscience Reference
In-Depth Information
expressions have distinct characteristics and support unique species. Even within a
region, seasonal forests can vary considerably from deciduous to evergreen dry
forests.
In Mexico and Central America, the seasonal forests are found along the west
coast as well as on several islands in the Caribbean. The South American countries
of Brazil, Bolivia, Paraguay, and Argentina also hold substantial areas of Neotropi-
cal seasonal forests. Some of the most diverse dry forests in the world occur in
southwestern Mexico, in the Chaco of South America, and the caatinga in north-
east Brazil. Seasonal forests occur in Africa along the margins of the rainforests of
West and Central Africa and are interspersed with savannas along the eastern
coast. Madagascar has a remnant tropical dry forest along its western coast. In
Madagascar, the seasonal forests support a unique assemblage of plant and animal
species found nowhere else. The Asian-Pacific region—India, Southeast Asia, the
islands of Indonesia, New Caledonia, and Australia—have seasonal forests greatly
influenced by seasonal monsoons. These seasonal forests house an exceptionally
diverse group of large terrestrial mammals. In each region, plants and animals have
evolved similar adaptive responses to dramatic seasonal changes in rainfall.
Formation and Origin of the Tropical Seasonal Forest Biome
The origin of this biome is similar to that of the Tropical Rainforest Biome
explained in Chapter 2 of this volume. Tropical seasonal forests developed along
the margins of the rainforest, while the supercontinental landmass of Pangaea was
present during the Permian. During the Mesozoic Era, Pangaea split into two large
landmasses, Gondwana in the south and Laurasia in the north, creating large-scale
climate change. The large Gondwanan landmass contained the tropical forests of
South America, Africa, Madagascar, Asia, India, and Australia. As the tectonic
plates began to separate, South America (with Antarctica) and Australia began to
move away from Africa. In the early Cretaceous Period (around 120 mya), Mada-
gascar and India separated from the southern landmass and traveled northeast, col-
liding with Asia. Madagascar became an isolated island in the Indian Ocean.
Later, the Australian landmass broke off and traveled eastward. South America,
Australia, and Africa became isolated island continents allowing for the evolution
of a unique set of plants and animals. On the northern landmass of Laurasia, North
America was connected to Europe and Asia and began to slowly move north.
Tropical seasonal forests were widespread around 65-50 mya, in the early Ter-
tiary Period. Changing climate brought increasing seasonality, with a distinctive
wet and dry season in parts of the tropics. This caused the tropical rainforest to
shrink, and the seasonal forest to expand. Climate continued changing, shifting
from seasonal to less seasonal throughout the Pleistocene. During interglacial peri-
ods, when warmer, wetter, and less seasonal patterns returned, the rainforests
expanded and the seasonal forests became restricted and fragmented.
