7 Tropical environments
7.4 Sustainable management of tropical environments Sustainable agroforestry, Santa Rosa rainforest, Mexico
Revised
About 30,000 Popoluca Indians live in southern Mexico. The Popoluca of Santa Rosa farm the Mexican rainforest, using a form of agriculture known as the milpa system (Table 7.1), which resembles shifting cultivation but which mimics the natural rainforest: l This is a labour-intensive form of agriculture, using fallow. l It is a diverse form of polyculture with over 200 species cultivated, including maize, beans, cucurbits, papaya, squash, water melons, tomatoes, pineapples, chayotes, oregano, coffee and chili. l Coffee is sold for cash. l Two crops are planted annually. l Fields are usually dug with digging sticks although a few households use ploughs.
Sustainable agroforestry involves farming forests without destroying the natural environment or putting excessive strain on resources.
The variety of plants found in a natural rainforest is mirrored by using shifting cultivation of crops with different requirements. For example, lemon trees, peppervine and spearmint are heliophytes – light seeking – and prefer open conditions not shade. Coffee, by contrast, is a sciophyte – preferring shade – while the mango tree requires damp conditions. The close associations that are found in natural conditions are also seen in the milpa system. For example, maize and beans go well together, as maize extracts nutrients from the soil whereas beans return them. Tree trunks and small trees are left because they are useful for returning nutrients to the soil and preventing soil erosion. They are also used as a source of material for housing , hunting spears and medicines. As in a rainforest, the crops are multi layered, with tree, shrub and herb layers. This increases NPP, because photosynthesis is taking place on at least three levels, and soil erosion is reduced, as no soil or space is left bare. In all, 244 species of plant are used in the farming system. Most of the crops are self seeding, which reduces the cost of inputs. The Popolucas show a high level of ecological knowledge in managing the forest. Table 7.1 A comparison between the milpa system and the new forms of agriculture
114
Milpa system
Tobacco plantations or ranching
NPP
High, stable
Declining
Work (labour)
High
Higher and increasing
Inputs
Few
Very high: 2.5–3 tonnes fertiliser/ha/pa
Crops
Polyculture (244 species used)
Monoculture (risk of disease, poor yield, loss of demand and/or overproduction)
Yield (compared with inputs)
200%
140% if lucky
Reliability of farming system
Quite stable
High-risk operation
Economics
Mainly subsistence
Commercial
Income
None/little
More
Carrying capacity
Several families/4 ha plus livestock
1 family on a plantation (200 ha); ranching – 1 ha of good land/cow, 20 ha of poor land/cow
Cambridge International AS and A Level Geography Revision Guide
