In places where the climate is suitable, trees are the climax vegetation[citation needed]. In some of the cool temperate regions, conifers tend to predominate, but in much of the southern hemisphere, the tropics, or in warm-temperate climates, broad-leaved trees are more common. Shade tolerance in young trees varies between species, and may determine the pattern of forest succession. More than half the species of terrestrial plants and animals on the Earth are thought to live in tropical rainforests even though these occupy just five percent of the land area.[34] In tropical regions with a monsoon climate, where a drier part of the year alternates with a wet period, different species of broad-leaved trees dominate the forest, some of them being deciduous.[35] Tropical regions with a drier savanna climate have insufficient rainfall to support dense forests[citation needed]; the canopy is not closed and plenty of sunshine reaches the ground which is covered with grass and scrub. Acacia and baobab are well adapted to living in such areas.[36] In cool temperate parts of the world, particularly in the northern hemisphere, deciduous broad-leaved trees tend to be replaced by conifers. The long cold winter is unsuitable for plant growth and trees must grow rapidly in the short summer season when the temperature rises and the days are long. Light is very limited under their dense cover and there may be little plant life on the forest floor although fungi may abound.[37] Similar woodland is found on mountains where the altitude causes the average temperature to be lower thus reducing the length of the growing season. Climax vegetation is the vegetation which establishes itself on a given site for given climatic conditions in the absence of major disturbance after a long time (it is the a ymptotic or quasi-equilibrium state of the local ecosystem). Tropical evergreen forest is an example of climax vegetation, as are temperate forests, tundras, savannahs, grassland etc. These major vegetation types are broadly governed by the latitude of the region in which they occur. Within these regions variants exist, dependent upon altitude, geographical location and environment, local prevailing micro-climate and soil or rock type. Thus, in temperate regions, beech forests tend to populate chalky soils and oak forests tend to prefer clays and mountain, heath, cliff, estuarine or coastal areas will have their own variations. An ecosystem which has reached its climax is more resilient to perturbations (climatic or anthropic) than an artificial plantation.[citation needed] This Picture indicates Montana's climax vegetation at the time of 9/8/2010. Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation,[1] but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea.[2][3] Usually, the term monsoon is used to refer to the rainy phase of a seasonally-changing pattern, although technically there is also a dry phase. The major monsoon systems of the world consist of the West African and Asia-Australian monsoons. The inclusion of the North and South American monsoons with incomplete wind reversal has been debated.[4] The term was first used in English in British India (now India, Bangladesh and Pakistan) and neighbouring countries to refer to the big seasonal winds blowing from the Bay of Bengal and Arabian Sea in the southwest bringing heavy rainfall to the area.[5][6] The south-west monsoon winds are called 'Nairutya Maarut' in India.