Crop expansion and conservation priorities in tropical countries

Abstract

Expansion of cropland in tropical countries is one of the principal causes of biodiversity loss, and threatens to undermine progress towards meeting the Aichi Biodiversity Targets. To understand this threat better, we analysed data on crop distribution and expansion in 128 tropical countries, assessed changes in area of the main crops and mapped overlaps between conservation priorities and cultivation potential. Rice was the single crop grown over the largest area, especially in tropical forest biomes. Cropland in tropical countries expanded by c. 48,000 km(2) per year from 1999-2008. The countries which added the greatest area of new cropland were Nigeria, Indonesia, Ethiopia, Sudan and Brazil. Soybeans and maize are the crops which expanded most in absolute area. Other crops with large increases included rice, sorghum, oil palm, beans, sugar cane, cow peas, wheat and cassava. Areas of high cultivation potential-while bearing in mind that political and socio-economic conditions can be as influential as biophysical ones-may be vulnerable to conversion in the future. These include some priority areas for biodiversity conservation in tropical countries (e.g., Frontier Forests and High Biodiversity Wilderness Areas), which have previously been identified as having 'low vulnerability', in particular in central Africa and northern Australia. There are also many other smaller areas which are important for biodiversity and which have high cultivation potential (e.g., in the fringes of the Amazon basin, in the Paraguayan Chaco, and in the savanna woodlands of the Sahel and East Africa). We highlight the urgent need for more effective sustainability standards and policies addressing both production and consumption of tropical commodities, including robust land-use planning in agricultural frontiers, establishment of new protected areas or REDD+ projects in places agriculture has not yet reached, and reduction or elimination of incentives for land-demanding bioenergy feedstocks.

Figure 1. Harvested area of major crops in tropical countries, 1980–2008.

The top ten crops in terms of their area in 2008 are shown. Oil palm and cow peas, which were the only two crops not on this list but which were in the top ten by area increase from 1999–2008, are also shown. Harvested areas of all other crops than these 12 are combined. Linear regressions used to assess recent rates of change in harvested area are shown. Source: .

Figure 2. Total area of cropland in biomes within tropical countries.

Shaded portions of bars show (A) total area of cropland in each biome, and (B) proportion of 5-min grid cells with <10% or ≥10% cropland cover, assessed from cropland map of . Lakes, rock and ice, tundra, temperate and mediterranean biomes are excluded.

Figure 3. Area of different crops as a proportion of cropland in biomes within tropical countries.

The top 12 tropical crops (see text) are identified. The width of each bar in this figure is equivalent to the width of the brown portions of the bars in Figure 2A. Source: .

Figure 4. Increments in the area devoted to cropland in tropical countries.

Circles show absolute increment over the period 1999–2008, with scale exaggerated 10 times for ease of interpretation. Shading indicates percentage of each country occupied by annual crops in 2008. Countries not defined as tropical are shaded grey. Maps are based on land data, for (A) arable land (annual crops) and (B) permanent cropland (perennial crops). Source: .

Figure 5. Areas of land with cultivation potential for selected crops of (A) wetter climates and (B) drier climates.

Maps are based on four wetter-climate crops (cassava, rice, sugar cane and oil palm) and eight drier-climate crops (beans, cow peas, groundnut, maize, millet, sorghum, soybeans and wheat). The map shows cultivation potential for the crop for which each 5-min grid cell is most suitable. Cultivation potential is calculated as the “agro-climatically attainable yield” for each rainfed crop as a percentage of the global maximum for that crop .

Figure 6. Areas of land with cultivation potential (blue) in relation to current cropland (red).

This is illustrated for (A) Neotropical countries, (B) tropical Africa and (C) tropical Asia/Australia. Shades of blue indicate cultivation potential for the crop for which each 5-min grid cell is most suitable. Cultivation potential is calculated as the “agro-climatically attainable yield” for 12 major tropical crops as a percentage of the global maximum for that crop . Shades of red indicate cropland extent in the year 2000, from . The darker shades indicate values above the median. Land which is suitable for one or more crops, and which is already cultivated, is mapped in shades of purple. Land with no cultivation potential for these crops, and no cropland, is mapped in white, and land outside tropical countries is shaded grey.

Figure 7. Cropland extent and cultivation potential within priority areas for biodiversity conservation in tropical countries.

Cultivation potential is defined as in Figure 5. The open symbols show the mean cultivation potential of all land in each set of priority areas, while the filled symbols show the mean cultivation potential of land that had not yet been converted to cropland as of 2000. Inset from shows conservation priority templates placed within the conceptual framework of irreplaceability and (retrospective) “vulnerability” and coloured accordingly (reprinted with modification, with permission from AAAS). “Proactive” conservation priorities are those in areas which are not yet considered to be highly “vulnerable” to conversion, while “reactive” priorities are those in areas where there has already been much habitat conversion. Abbreviations: Biodiversity Hotspots (BH), Centres of Plant Diversity (CPD), Crisis Ecoregions (CE), Endemic Bird Areas (EBA), Frontier Forests (FF), Global 200 Ecoregions (G200), High Biodiversity Wilderness Areas (HBWA), Last of the Wild (LW), Megadiversity Countries (MC). Mean across all tropical countries shown by grey symbols.