Rainforest Journal

Rainforest Info, Images, and Adventures.

Definition of a rainforest


All over the world, the word rainforest is used rather loosely to denote a type of forest with lots of greenery and rain, right? Well, here I’d like to get into the specifics of the term, rainforest, and define it. I think we should all have a better understanding of this much used term.

True rainforest as a matter of fact, only exists in certain parts of the world. It has to mean lots of rain with no seasonality at all. Generally, this has come to be accepted as areas with rainfall between 1500-2000 mm per month, hot and humid all year round, and a stratified forest where there is a emergent, canopy, undergrowth, and ground layer. The forest also has to be evergreen in perpetuity. So if a “rainforest” is missing one or more of these elements, it cannot really be called a rainforest, but then again, we have other terms for these types of forest, like monsoonal forest, semi-evergreen rainforest and temperate rainforest, among others.

At least as far as I know, here in Malaysia, the vast majority of forest that used to cover this country is called lowland evergreen rainforest, with rainfall all year round, tall trees, having a stratified layer, and no distinct seasonality, save for a few small regions mainly in the north, near the Thai border.

In the Amazon, large tracts are actually not true evergreen rainforest, contrary to popular opinion, but have a distinct seasonality (a massive drought ravaged the Amazon a few years ago). Also, much of the basin around the river is a rather short stature forest (upper canopy 20-27 m high) that borders on freshwater swamp forest, seasonally inundated by the Amazon. But from the air, aerial photos of the Amazon often show a vast carpet of green, which many people understandably call, “rainforest.” That said, there are also many areas, like along the Andes foothills and in Central America, where true evergreen rainforest exists.

The same rationale goes for vast tracts of the Congo “rainforest,” that is actually more akin to semi-evergreen rainforest at best. There are many open areas in the Congo forest that have tall grass and bushes, while the more dense areas are populated by many types of trees that shed their leaves on a periodic basis. Comparable areas can be seen in the “rainforests” of Indochina and India.

In Malaysia however, the forests are very uniform, and the rainfall does not really vary much from year to year. With the exception of El Nino induced droughts and also heavier rain during the end months of a year, most forest areas in Malaysia can be classified as “true evergreen rainforest.” The canopy is unbroken, and there are no open areas populated with bushes; although some trees are seasonal, most of the trees are true evergreen trees.

Perhaps this is the reason why you can find very tall trees here? On the island of Borneo, tall trees 60-70 m tall are very common, especially in the northern half of Borneo. Some trees even exceed 80 m high (but widespread logging decimated almost all of them). Ideal conditions permit the rainforest to develop to its full glory, complete with all the strata you would normally associate with a “true rainforest.” Biodiversity is also extremely high, resulting in the most species rich rainforest anywhere on earth (on most biodiversity/area ratios, Malaysia has the highest ratios in the whole world).

But for convenience’s sake, we and most people would probably just call everything – Jungle….

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