Habitat fragmentation is defined as the breaking apart of continuous habitat in to distinct pieces, and can be understood in terms of three interrelated processes; a reduction in the total amount of original vegetation, subdivision of the remaining vegetation in to fragments, and the introduction of new forms of land use to replace lost vegetation, usually in the form of agriculture (Bennett & Saunders, 2010).

Forests and other natural habitats have been converted for agricultural use for as long as humans have walked the earth, and while most of the focus recently has been on the conversion of tropical rainforests to agricultural plantations, landscapes all throughout the world are still being converted, and in the developed world, natural landscapes are a shadow of their former selves.

Of the 16 million km2 of tropical rainforests that once existed, just around 9 million km2 exists today, with forests in South East Asia disappearing most rapidly. Tropical dry forests along the Central American Pacific coast now cover just 1% of the total land cover they used to, and from 1990 to 2000, over 1% of all mangroves were lost annually. By 1990, more than two-thirds of Mediterranean forests and woodlands had been lost, mainly for conversion to agriculture, and in eastern USA and Europe, old growth broad leaf forests have nearly disappeared. 10-20% of the world’s grasslands have been destroyed for agriculture, and in South America, more than half of the biologically rich cerrado savannas, which formally spanned over 2 million km2, have been converted in to soy fields and cattle pastures in recent decades (Laurance, 2010). It is estimated that over the past 3 centuries, the global extent of cropland has risen from around 2.7 to 15 million km2 (Laurance, 2010).

The conversion of tropical rainforests for agricultural purposes throughout Indonesia and Malaysia has been immense. Today, approximately 45% of Indonesia’s workers are engaged in agriculture, with 31 million hectares of land under cultivation, with 35-40% of that land devoted to the production of export crops. In Indonesia, there are three main types of agricultural farming; smallholder farming, smallholder cash cropping, and about 1,800 large foreign-owned or privately owned estates. Small scale farming is usually carried out in modest plots, and usually focuses on the cultivation of rice for subsistence, with vegetables and fruit also grown. These products are also grown as cash crops for export, with rubber also cultivated, and making up around 20% of all cash crop exports. Of estate grown crops, rubber, tobacco, sugar, palm oil, hard fiber, coffee, tea, cocoa and cinchona are the most important (Encyclopedia of the Nations, 2011).

The conversion of forest to agriculture involves the chopping down of trees, and the corresponding loss of biodiversity. Although very few animal species can live in any type of plantation, if managed well, plantations can still retain some of the ecosystem functions of tropical rainforests.

 In their undisturbed state, tropical rainforests have a virtually closed canopy, comprise millions of different species of trees, leaves and animals, and have a forest floor covered in a thin layer of leaf litter, underlain by a highly permeable topsoil, a formation with means they have one of the lowest surface erosion rates of any form of land use (Critchley & Bruijnzeel, 1996). Tropical forests also produce an extraordinary amount of plant biomass, caused by the compact nutrient cycle of these ecosystems, with plant nutrients that enter the forest ecosystem, through rain, dust and aerosols, being cycled continuously between the canopy and the soil, with only small amounts leaking out of the system (Critchley & Bruijnzeel, 1996). This delicately balanced cycle is disturbed when trees are cut down.

Of all the methods of clearing trees, manual clearing is the least damaging to the soil. However, it is a slow and expensive method, particularly when large areas of forest need to be cleared. Instead, most plantations, particularly those owned by large corporations, will use heavy machinery, often with root takes, which are used to uproot tree stumps. When the timber is extracted, forest debris will often be set alight, a cheaper and easier way of clearing any vegetation still left. After clearing, this land will be planted with crops.

The soil quality and productivity of plantations depends heavily on both the methods used, and the crop being cultivated. Tea, for example, is usually grown in areas with year round abundant rainfall, and is often cultivated in areas of high altitude, where terraces will be constructed before planting. Tea plantations can last for several decades before production declines, and of all the land use systems that replace tropical rainforests, it is usually considered to be one of the most effective, with respect to soil erosion, because tea trees often grow tall, and form a closed canopy (Critchley & Bruijnzeel, 1996). In contrast, coffee trees need wider spacing, to allow access for picking and spraying, so coffee plantations have a much sparser canopy, and are more susceptible to soil erosion and invasive weeds. Rubber plantations, which are abundant throughout Sumatra, require deep, relatively fertile soil and thrive best on flat land. To establish rubber plantations, land is clear stumped, to avoid disease transmission to the trees, and newly planted rubber plantations are susceptible to high levels of erosion and runoff (Critchley & Bruijnzeel, 1996). 

When a natural forest is converted to a plantation, the reduction in plant cover increases the overall catchment of water, and it can often take years, when crops and trees start growing, for this water yield to decrease. Even then, crop plantations almost always use less water than original forests, and in areas surrounding plantations, runoff waters, usually discolored with sediment, can be observed. However, although the process of conversion is highly destructive, the destruction of the lands services can be limited by using appropriate clearing practices and land management techniques, including controlled drainage, bench terraces, contour farming or the introduction of biological barriers, like hedges or woodland (Critchley & Bruijnzeel, 1996).  

Over the last few decades, the agricultural commodity that has received the most attention and is considered to have caused the most destruction to primary forests throughout Indonesia and Malaysia is palm oil. Palm oil (Elaeis guineenis) is native to Africa and was first planed in Indonesia in 1848. It is suited to tropical regions within 12 to 15 degrees north and south of the equator, where the average rainfall is between 2,000 and 2,500 millimeters per year. As the palm oil harvest declines during the dry season and the flowering period and maturation of the fruit is affected by temperature, humidity needs to be high, between 80 to 90%, and the temperature needs to lie between 29 to 30 degrees (Rautner et al, 2005). Borneo and Sumatra are therefore ideal, and thousands of hectares of lowland tropical rainforest, habitat for the islands’ orangutans, tigers, elephants, rhino’s, leopards, gibbons, and numerous other species, has been converted to make room for this oil.

Palm oil, which has the highest per hectare yield (4-8 tons) of all edible oils, is now the most important vegetable oil in the world. In 2002, palm oil, and palm kernel oil, accounted for approximately 23% of the world’s edible oil production, and 51% of global trade in edible oils. Indonesia is now the world’s largest exporter of palm oil, with Malaysia a close second, and between 2016 and 2020, the projected production by Indonesia is around 18,000 million tons, or 44% of world production, while Malaysia’s estimated output will be 15,400 million tons, or 37.7% (Rautner et al, 2005).

Palm oil plantations are usually established after large areas of forest have been cleared by heavy machinery. After the timber has been extracted and sold on the international legal or illegal timber market, left over debris is usually set alight. The use of fire to clear forest is one of the most destructive practices, and is partly responsible for the extensive fires that have ravaged forests throughout Indonesia and Malaysia in recent years, including the devastating fires of 1997 and 1998 (Rautner et al, 2005; Harrison et al, 2009).

Palm oil trees are single stemmed and can grow up to 20 meters tall, and have leaves that grow up to 3-5 meters long. The palm fruits start bearing 2-3 years after the palm tree has been planted, and they take around 5 months to mature from pollination, growing in large bunches. Oil is extracted from both the pulp of the fruit, which becomes palm oil, and the kernel, which becomes palm kernel oil.  In order for the trees to yield fruit earlier, and to control invasive weeds, pesticides are regularly used, including the highly toxic Paraquat, and have been blamed not only for the decreased level of biodiversity in palm oil plantations, but also for poisoning thousands of plantation workers (Rautner et al, 2005; WRM, 2005). Forest conversion for palm oil plantations results in a loss of 80% of plant species, and in palm oil monocultures, research has shown 80-90% of mammals, reptiles and bird species found in tropical forests cannot survive (Rautner et al 2005). It is feared that the increasing demand for palm oil in both household products and as a biofuel will see even more areas of lowland forest converted to plantations, and a continued decrease in populations of endangered species.

The conversion of forests for agriculture is a historic process that is unlikely to stop in the near future. So far in Indonesia and Malaysia, and wider parts of the world, this conversion has taken place in lowland areas home to some of the world’s most endangered animals. Managing and preventing future forest loss, while considering the needs of a rapidly increasing human population, will be one of the greatest environmental challenges of the next few decades.

Hopefully lessons can be learned from one of the greatest environmental disasters in history, Indonesia’s ‘Mega Rice Project’.  The Mega Rice Project was a plan by former Indonesian president Suharto to make Indonesia self sufficient in rice production. The project proposed to convert 796,000 hectares of peat swamp forest in Central Kalimantan in to rice fields, with an additional settlement program to relocate 316,000 transmigrant families to the area. Despite not carrying out a cost benefit or sensitivity analysis, and repeated warnings by scientists that the project would fail and the depth of the peat made it unsuitable for conversion, Suharto went ahead with the project. Around $175 million was spent on the scheme, half of which went towards digging canals to drain the peat swamp, which was so deep it subsided . After Suharto fell from power in 1998, the project was abandoned, and no rice has ever been grown on the land. Today, the Mega Rice Project area is a barren wasteland, where the transmigrants are unable to grow rice or enough crops to survive, where poverty is rife, where orangutans and other wildlife are scarce and live in fragmented patches of forest, and the area is prone to illegal logging and frequent forest fires (Rautner et al, 2005).

 References

Bennett A. & Saunders D. (2010). Habitat fragmentation and landscape change. In Conservation biology for all. Oxford University Press

Critchley W. & Bruijnzeel S. (1996). Environmental impacts of converting moist tropical forest to agriculture and plantations. UNESCO

Encycolpedia of the Nations (2011). Indonesia. Encyclopedia of the Nations

Harrison M. et al (2009). The global impact of Indonesian forest fires. Biologist.

Laurance W. F (2010). Habitat destruction; death by a thousand cuts. In Conservation biology for all. Oxford University Press

Rautner et al (2005). Borneo- Treasure island at risk. WWF

World Rainforest Movement (WRM). (2005). Oil palm plantations- No sustainability possible with Paraquat.