The rubber-enriched fallow

Although estates adopted monoculture right from the beginning in order  to maximize rubber production, farmers immediately exploited the possibility of growing rubber in a very extensive way, by enriching their fallow (‘belukar’ in Indonesian) with unselected rubber seedlings that were freely available.

Planting rubber during, or after, upland rice demanded only marginal extra work, with no risks and - more importantly for local farmers - no costs. Indonesian farmers immediately jumped into this new opportunity for rubber production and began to collect seeds in estates in order to plant their own rubber trees. Unselected rubber trees proved to be very adaptive to this "new” environment. This system has been called “jungle rubber” (hutan karet) by Indonesian farmers who considered that it was basically a fallow enriched with rubber trees

The advantages of jungle rubber were clear: no cost; no labor required for maintenance during the immature period; and sizeable income diversification with fruits, rattan, timber and other non-timber forest products harvested from the agroforest. Although rubber tapping was delayed compared to rubber monoculture in estates, yields still provided an attractive income, especially when improved planting material was introduced in the 30-40s. Indirect environmental benefits included soil conservation and rehabilitation of degraded lands.

Creating complex agroforestry systems

Rubber estates had initiated their own research programs in the 1920’s, and the introduction of clones as improved planting material was the most important improvement in terms of yield. Meanwhile, farmers developed several other "endogenous innovations" at no-cost, such as planting in lines and minimal weeding (once a year) mainly through the improvement of some rubber farming practices. At this stage, the aim was clearly to establish rubber systems which minimized capital and labor investment, and farmers made a perceptible shift from a "fallow enriched with rubber" towards a more genuine "complex rubber agroforestry system". The productivity of jungle rubber was and still is low (500 kg/ha/year of rubber) compared to that of clones on estates (1500 to 1 800 kg/ha/year). After experimenting with endogenous innovations, farmers became more interested in also adopting such "external innovations" as clones, fertilization and improved tapping systems.

The constraints of jungle rubber have been well identified (Gouyon, 1995) :

• a delay in production of the rubber trees which are tapped after 9 to 15 years after panting (5 to 6 years in monoculture systems), and
• a relatively low productivity (compared to clonal plantations). In many regions, jungle rubber systems were found economically obsolete and many have disappeared to the profit of oil palm or clonal rubber plantations.

Continuous innovations

Farmers with access to clonal rubber in monocultures trough projects in the 1970’s also began to develop additional innovations, such as inter-cropping during the immature period and planting (or from natural regeneration) perennials such as fruit and timber trees. They thus created an "improved rubber-based complex agroforestry system" where the original aim of improving the fallow disappeared in favor of the desire to establish a more productive cropping system. Population increase, land scarcity in some areas, and introduction of other more remunerative cropping opportunities eventually combined to force farmers to adopt a more productive Rubber Agroforestry System (RAS).  Current agroforestry research focuses on the potential to integrate indigenous knowledge on jungle rubber with external innovations that will improve productivity while still conserving environmental and biodiversity benefits offered by traditional agroforestry practices.

Rubber has proved to be adapted to meet the challenge with rice cultivation particularly in the rainy season. This is an important feature, because labor is the main available factor of production in the lack of any capital when land is still plentiful. Therefore, from the beginning, rubber and ladang rice could merge with flexibility in existing farming systems. Meanwhile, this co-cultivation has enabled migrants to settle down in these areas in increasing numbers, therefore triggering a change in population density and pressure on available resources. Average population density in Sumatra is now 35 inhabitants/km² and land is becoming scarce in some provinces (North and South Sumatra, Lampung). According to Dove (1993), "the comparative ecology and economy of rubber and upland swidden rice result in minimal competition in the use of land and labor, and even in mutual enhancement, between the two systems". Jungle rubber and shifting cultivation are not at all antinomic, as the two systems can coexist in local farming systems. This system can be described, from a botanical point of view, as a “complex agroforestry system” (de Foresta and Michon, 1992).

Jungle rubber and deforestation

It is clear that rubber has also triggered deforestation (Prasetyo et al, 1995) and that timber concessions, with the example of South-Sumatra, has less impact on forest cover than any other land uses. The paradox lies in the fact that now jungle rubber is the main reservoir of biodiversity and that rubber agroforestry systems are among the best-adapted systems for preserving biodiversity, when compared to other land use system using oil palm, coconut, coffee, cocoa or pulp trees.

Rubber has proved to be very adaptable to this “new” environment, compared to that of monocultivated estates. The major advantage of jungle rubber or clonal RAS lies in biodiversity conservation, because in such complex systems, biodiversity is close to that measured in a primary forest or an old secondary forest, when compared to amature jungle rubber.  Environmental benefits are measured in in terms of soil conservation (Sethuraj, 1996) and water management due to the forest-like characteristic of jungle rubber.