Visitors are often surprised that the trees in tropical rain forests are not taller. In many tropical rain forests, the trees are not that tall at all. In North America, much taller trees are found in the north-west temperate rain forests. And in Australia, the biggest flowering trees in the world are in the Eucalypt open forests in the south-east of the continent. There are many big trees, but many of those larger specimens were taken out by loggers for their timber, and too see good remanant examples of unlogged rain forest, it is often necessary to hike for a few hours into the forest. In the tropical rain forest there is a high diversity of different forms and sizes.
Climbers can include various types of plants. They are defined by their common method of climbing other plants to reach sunlight without using their own support. They are unified by their method of growth, and different climbers are not necessarily closely related. They can be divided into four basic types based on their climbing methods. Generally, the greener shorter-lived climbers are known as 'vines, and the longer-lived woody vines are known as 'lianas' although this terminology varies with language and geography and is not really scientific.
Climbers such as vines and lianas are one o the most obvious aspects of this ecosystem. While vines are found al over the world, over 90% of species are found in the tropics (reference). In Australia, this importance is reflected in the classification system where some rainforests are known as ‘vine forests’ (e.g.; Webb and Tracey 1987).
In some areas, there may be almost as many climber species or individuals as there are trees. Once secure, the lianas may develop large woody stems as, to use a jungle cliché, 'big as a man's thigh', with a record of one liana being 60cm in diameter. Barring collapse, some of these woody climbers may be as long-lived as many of the trees of the forest.
Different species of climbers have developed different parts of their anatomy to climb up. Which part of the plant has evolved this is in a large part determined by the phylogeny of the plant; that is what group of related plants it belongs to. The climbing 'rattan palms' have several methods; there are hooks on the undersides of the leaves and on the stalks of many species. Many rattans in the genus Calamus (found in Asia and Australia) have developed the tendril which normally carries the inflorescence (the flowers) and fruits into a climbing appendage. It is light and armed with re-curved hooks. Any sort of disturbance, such as a slight wind, may end with the light tendril hooking onto nearby vegetation and thus giving the plant a foothold into the surroundings, enabling it to climb. In contrast, the vigorously growing 'Supplejack vine' Flagellaria indica climbs by using it's leaves. The ends of the leaves have elongated and curl around to catch onto the surrounding vegetation. Vines in the wine family Vitaceae have tendrils that curl out from their main stem opposite their leaves (Jackes 199).
Climbers generally do what their name suggests; they climb other vegetation to gain access to sunlight. There are many more climber species in the tropics than there are in the temperate areas. In early studies, some species of climber at these higher latitudes apparently grew in a particular pattern to take advantage of the sun; in the northern hemisphere they spiraled up the trunk to the left, while in the southern hemisphere they grew to the right (Whitten et al 1987). However, as most rainforest and therefore climber species are found in the equatorial regions within the tropics, logically the effect of the sun (if any) is negated. And in fact later studies have found that a higher percentage of climbers have an anti-clockwise bias when growing up the support (Martin 1992-), a bias which is presumably determined through phylogeny.
Climbers in the rainforest create some of the most interesting and aesthetically pleasing patterns and formations. Many of these can be explained by simple biology. Many of the lianas seem to hang in the air, naturally creating the question of how they climbed up through empty space. The answer is that when younger, these climbers grew up trees that have since disappeared through death and/or collapse. Similarly, some of these climbers hanging in the air create a pleasing spiral pattern hanging freely in the air. These can be called 'ghost branches' as when the climber was younger it grew around a branch or tree that has since disappeared, but the plant retains it's spiral growth pattern.
Climbers can also be looked at from the other side; from the perspective of the trees that have to support them. The question of why do climbers not take over the rainforest frequently arises. It has been suggested that the trees of the rainforest may have evolved various adaptation to defend themselves against such a scenario. Palm trees are an obvious part of the lowland rainforest, and perhaps one of their secrets is the fact that they can avoid the invasive attack of climbers. They do this because of the way they grow; for they grow from one point at the apex, dropping their old leaves as they become taller. There are no permanent lateral branches and just one smooth trunk, thus there is nowhere for the climbers to attach (Attenborough 1995)
Nevertheless, climbers are a ecologically and phylogenetically significant part of the rainforest. Some climbers reach enormous sizes. One climber in South America was noted to cover over 60 individuals of trees. The 'rattan palms' of Asia and Australia develop the longest stems of any plant in the world, with records of stems over 500 feet (Attenborough 1995).
Epiphytes are another obvious component of rain forests. They are plants that grow on other plants. Visitors often mistake them for bird’s nests, tree parasites, or part of the tree. It is not uncommon to see a large number of both species and individuals on the one tree. Many can grow to a size where they are larger in diameter than the tree that supports them.