Seasonal tropical forest

Tropical seasonal climate sub-types:
  Am—Tropical monsoon climate.
  Aw/As—Tropical savanna climate.
(note: Af in light green is Tropical rainforest)

Seasonal tropical forest, also known as moist deciduous, semi-evergreen seasonal, tropical mixed or monsoon[1] forest, typically contains a range of tree species: only some of which drop some or all of their leaves during the dry season. This tropical forest is classified under the Walter system as (i) tropical climate with high overall rainfall (typically in the 1000–2500 mm range; 39–98 inches) and (ii) having a very distinct wet season with (an often cooler “winter”) dry season. These forests represent a range of habitats influenced by monsoon (Am) or tropical wet savanna (Aw/As) climates (as in the Köppen climate classification). Drier forests in the Aw/As climate zone are typically deciduous and placed in the Tropical dry forest biome: with further transitional zones (ecotones) of savannah woodland then tropical and subtropical grasslands, savannas, and shrublands.

Distribution

Main article: Global 200 § Tropical and subtropical moist broadleaf forests
Extreme differences are very much evident between the wet and dry seasons in a tropical seasonal forest. The image to the left shows Bhawal National Park in central Bangladesh during the dry season, while the image to the right depicts the same area during monsoon season.
Trees at Cat Tien National Park: showing seasonal forest structure in the early dry season (December)
Seasonal forest in Northern Thailand

Seasonal (mixed) tropical forests can be found in many parts of the tropical zone, with examples found in:

Emergent tree rising above the main canopy in Khao Yai National Park forest

Climate

The climate of seasonal forests is typically controlled by a system called the Intertropical Convergence Zone (ITCZ), located near the equator and created by the convergence of the trade winds from the Northern and Southern Hemispheres. The position of these bands vary seasonally, moving north in the northern summer and south in the northern winter, and ultimately controlling the wet and dry seasons in the tropics.[7] These regions appear to have experienced strong warming, at a mean rate of 0.26 degrees Celsius per decade, which coincides with a global rise in temperature resulting from the anthropocentric inputs of greenhouse gases into the atmosphere. Studies have also found that precipitation has declined and tropical Asia has experienced an increase in dry season intensity whereas Amazonian has no significant pattern change in precipitation or dry season.[8] Additionally, El Niño-Southern Oscillation (ENSO) events drive the inter-annual climatic variability in temperature and precipitation and result in drought and increased intensity of the dry season. As anthropogenic warming increases the intensity and frequency of ENSO will increase, rendering tropical rainforest regions susceptible to stress and increased mortality of trees and other plants.[8]

Onset dates and prevailing wind currents of the southwest summer monsoon.

Structure

As with tropical rainforests there are different canopy layers, but these may be less pronounced in mixed forests, which are often characterised by numerous lianas due to their growth advantage during the dry season.[9] The colloquial term jungle, derived from the Sanskrit word for "forest", has no specific ecological meaning but originally referred to this type of primary and especially secondary forest in the Indian subcontinent. Determining which strands of mixed forest are primary and secondary can also be problematic, since the species mixture is influenced by factors such as soil depth and climate, as well as human interference.

Characteristic biology

The fauna and flora of seasonal tropical mixed forest are usually distinctive. Examples of the biodiversity and habitat type are often well described for National Parks in:

Falling Waters in Korup National Park

References

  1. ^ Mongbay: Types of tropical forest (accessed 21 March 2017)
  2. ^ Beard, J.S.; Keneally, K.F. (1987), 'Rainforests of Western Australia'. In 'The rainforest legacy: Australian national rainforests study'. Special Australian heritage publication series 7(1), pp. 289–304
  3. ^ Webb, L. J. (Leonard James); Tracey, J. G. (John Geoffrey) (1982), An ecological survey of the monsoon forests of the north-western region of the Northern Territory, Australian National Parks and Wildlife Service
  4. ^ Russell-Smith, Jeremy; Dunlop, Clyde (1987), The status of monsoon vine forests in the Northern Territory: a perspective. In 'The rainforest legacy: Australian national rainforests study. Special Australian heritage publication series 7(1)
  5. ^ Stanton, J.P.; Fell, David. G. (2005). "The rainforests of Cape York Peninsula". Rainforest CRC – via National Library of Australia.
  6. ^ Leigh EG, Rand AS, Windsor DM (Eds. 1983) The ecology of a tropical forest. Seasonal rhythms and long-term changes. Oxford University Press 468 pp.
  7. ^ NWS JetStream – Inter-Tropical Convergence Zone. Srh.noaa.gov (5 January 2010). Retrieved on 28 March 2013.
  8. ^ a b Malhi, Yadvinder & Wright, James (2004). "Spatial patterns and recent trends in the climate of tropical rainforest regions". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences. 359 (1443): 311–329. doi:10.1098/rstb.2003.1433. PMC 1693325. PMID 15212087.
  9. ^ Ya-Jun Chen, Kun-Fang Cao, Stefan A. Schnitzer, Ze-Xin Fan, Jiao-Lin Zhang, Frans Bongers (2015) Water-use advantage of lianas over trees in seasonal tropical forests. New Phytologist, 205[1]: 128–136

See also