Framework for Analysis Conceptual Framework

A systems view of sustainability simply asserts that the withdrawals from the stock of a resource should not exceed the renewal rates. In the case of a non-renewable resource, the stock will necessarily deplete over time, and thus the issue becomes: How long can we continue to withdraw the resource at a given rate before we run out of it? Using this framework, we can assess the sus-tainability of a resource by identify the stocks, withdrawal rates, and renewal rates.

Land is a finite commodity on our planet. Although we can marginally increase the extent of land by reclaiming land from the ocean, it is essentially a limited resource. In that sense, it is clearly a nonrenewable resource. In the case of agriculture, there is a certain amount of potentially cultivable land on the planet that could be further extended through the use of irrigation, soil management, greenhouse production, etc.1 Otherwise, potential cropland area is a finite resource, and we can estimate how fast the current rate of utilization (i.e., net cropland increase = cropland expansion - abandonment) is depleting the resource (Figure 2.1). Forest area is also a finite resource. Forests provide multiple resources, including a source of potentially cultivable land and various forest products. Much of the deforestation in the world has resulted from converting land for agriculture (i.e., utilizing potentially cultivable land).

A large part of land is used for grazing, for livestock production. Livestock production, however, is moving toward "landless production" in feedlots. I will not focus on these trends here. For a review, see "Livestock's Long Shadows" (FAO 2007).

Potential cropland area

Net cropland increase (expansion minus abandonment)


Net cropland increase (expansion minus abandonment)


Forest area

Net deforestation (gross deforestation minus forest regeneration)

Figure 2.1 Systems view for evaluating sustainability of cropland and forest land resources. Net cropland increase or net deforestation depletes cropland and forest resources. By comparing the rates of use to the stock, estimates can determine how fast the resource is being lost.

Knowing current rates of net forest change (net deforestation = gross deforestation - forest regrowth) allows us to estimate the pace at which we are depleting forests.

In the case of food production, identification of the stocks, flows, and limits is more challenging. For simplicity, let us limit this thought exercise to crop production. Crop production is an annually renewable resource in the sense that every year we harvest the total amount of grain or other plant products accumulated over that year, and start all over again the following year. Thus, sustainable food production means maintaining this annual supply of crop products year after year as well as keeping up with increased food demand. To conceptualize this, imagine the stock as a "potential crop production" (i.e., a product of potential cropland area and potential maximum yields; see Figure 2.2). As discussed, potential cropland area is a nonrenewable finite resource. What about potential maximum yield? The yield of a crop (production per unit area) is a function of sunlight, carbon dioxide, water, nutrients, and adequate pollination service. Sunlight and carbon dioxide are available in plenty; the latter is increasing in the atmosphere due to human activities and will most likely benefit plant production. Water and nutrients are currently the key constraints to plant production; indeed, the miracle of the Green Revolution was to develop new crop cultivars that could take advantage of increased supply of water and nutrients, and therefore increase yields. Thus the question of maintaining and increasing yields into the future is really a question of whether we can continue to supply enough water and nutrients to crops. Finally, we must also consider the environmental impacts of agriculture. The process of expanding and intensifying agricultural production has already resulted, for example, in loss of species and biodiversity, modification of regional climates, alteration of water flows, and water quality (Foley et al. 2005; Tilman et al. 2002). Indeed, some studies indicate that the clearing of natural vegetation for cultivation may have the unintended consequence of reducing pollination

Figure 2.2 Systems view for evaluating sustainability of food production. Balance is between food supply and food demand. Is the land capable of providing the annual increases in production needed to meet food demand? Environmental impacts of increased production are not included in this framework but represent an important concern that must be addressed.

Figure 2.2 Systems view for evaluating sustainability of food production. Balance is between food supply and food demand. Is the land capable of providing the annual increases in production needed to meet food demand? Environmental impacts of increased production are not included in this framework but represent an important concern that must be addressed.

services (Kremen 2002). Similarly, intensification can degrade soils making it more difficult to increase future yields (Cassman 1999). Therefore, one of the unintended results of cultivation is that its environmental impacts may reduce potential maximum yields. To summarize, sustainability of food production requires us to address three questions:

1. Do we have enough land, water, and nutrients to maintain current food production?

2. Can we increase food production to meet increased future demand?

3. What are the environmental consequences of food production?

With forest production, limiting our discussion to timber, stocks and flows makes it relatively easier to conceptualize. The stock is essentially the growing stock of wood. This is a renewable resource because once a forest is logged, it can grow back, even though it may take several decades to regain full maturity. We can therefore examine whether current wood removal rates exceed the rates of forest regeneration. Forest regeneration rates depend on the climate, soils, and other biophysical conditions, and can range from a few decades (in the tropics) to a couple of centuries (in boreal regions).

As a final note, these analyses would likely overestimate the availability of resource in one sense: they examine the impact of current rates of resource use or extraction on the continued availability of that resource into the future. With continued population growth and increasing consumption, however, it is to be expected that resource use rates will increase into the future, therefore depleting resources even faster than estimated here. A more thorough analysis is beyond the scope of this chapter, since we do not have readily available estimates of future trends in resource use rates.

Sources of Data

The authority that monitors the status and trends in global agriculture and forests is the Food and Agricultural Organization (FAO) of the United Nations. According to FAO's website (FAO 2009a), one of its primary activities is to put information within reach through the collection, analysis, and dissemination of data to aid development. FAO does not engage directly in data collection, rather it uses its network to compile data as reported by member nations. In the case of agricultural statistics, FAO does this by sending out questionnaires annually to countries, and the compiled data are then reported in the FAOSTAT database (FAO 2009b). Forestry statistics are compiled every five years by FAO, also using a methodology whereby participating nations report their statistics to the FAO. In this most recent forest assessment conducted in 2005, FAO trained more than 100 national correspondents on the guidelines, specifications, and reporting formats (FAO 2005).

FAO statistics have, however, been widely criticized (Grainger 1996, 2008; Matthews 2001). Partly as a result, satellite-based remote sensing data have become more widely used in monitoring changes in the land. Satellite sensors offer a synoptic view of the Earth and a relatively objective method for mapping the entire planet. Recent estimates of deforestation using satellite-based methods have suggested that FAO statistics have overestimated deforestation (DeFries and Achard 2002; Skole and Tucker 1993). However, these data are still in the research and development mode; they are not consistently available for the entire planet over time. Moreover, while there is available satellite data on the geographic extent of land (i.e., forest area, cropland area), estimates of the global productivity of land (i.e., crop yields, forest growing stock) are not available. Therefore, despite criticisms of the FAO data, they continue to be widely used because (a) they are the only available source for comprehensive statistics on land resources (e.g., agriculture and forestry) and (b) they provide time-series data since 1961 for most variables. Thus, in this chapter, I use the FAO data, with the caveat that the numbers are only indicative.

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