fundamental ecosystem service, closely related to the ability of ecosystems to provide other services (Daily et al. 1997; MEA 2005b).

HANPP refers to the observation that land use alters ecosystem functions; in particular, ecological energy flows (Vitousek et al. 1986; Wright 1990; Haberl et al. 2001). For example, land conversions, such as soil sealing or clearings of pristine forests to gain agricultural land, alter ecosystem patterns and processes, and therefore have an impact on the NPP of these ecosystems. In addition, agricultural and forestry practices withdraw biomass energy from ecosystems for socioeconomic purposes (e.g., food or fuel harvest), thus reducing the amount of NPP that remains in ecological food chains. HANPP aggregates these two distinct effects of land use on the energy flow of ecosystems by calculating the difference between the NPP of potential vegetation (NPP0)—the vegetation that would prevail in the absence of human land use—and the fraction of the NPP of the actually prevailing vegetation (NPPact) that remains in ecosystems after harvest (Haberl et al. 2004, 2007). Changes in NPP that stem from land conversion are denoted as ANPPLC and biomass harvest as NPPh. Thus, the HANPP concept measures the impact of land use on the availability of energy within the ecosystems. It moves beyond measuring the extent of land under use, but integrates the effects of land use intensity (e.g., changes in NPP or harvest per unit of land) and quality of land (potential NPP) under use in one single metric.

A recent spatially explicit assessment of global HANPP (Haberl et al. 2007) has revealed the magnitude and spatial pattern of HANPP across the globe, indicating the varying intensity of land use across Earth's surface (Figure 5.1). According to Haberl et al., 23.8% of the potential global NPP are appropriated by humans and 53% of Earth's HANPP is used for biomass harvest for food, fuel, or feed and alterations of ecological productivity. The conversion of land for infrastructure or settlements accounts for only 4% of HANPP, but this land use type is characterized by HANPP rates above 70%, such as areas characterized by a high percentage of sealed soil (Haberl et al. 2007).

The second limitation with our current conceptualization of land is that it fails to account for connectedness (Schmitz 2008), or complex land transformation

Figure 5.1 Spatial pattern of the global human appropriation of NPP (Haberl et al. 2007; courtesy of PNAS).

chains and "land teleconnections." Similar to the concept of teleconnections in atmospheric sciences, land teleconnections are the linkages among land uses over large geographic distances: How do land use and resource demands in one region affect and drive land use change in another region? In an increasingly globalized economy, the places of production are often disconnected from the places of demand. For example, it is common for livestock to be raised in a region that is different from the place where the feed is produced, and for the animal products to be exported to still other areas.

Take, for example, the case of pig production in Denmark, where 25% of the feed requirements for the 25 million pigs produced each year is imported from Argentina. The demand for feed in Denmark has significant implications for the expansion of cropland in Argentina. Pig production in Denmark is an environmental concern inasmuch as it is responsible for a majority of the nitrogen loss from farm land to the aquatic environment. To encourage environmentally sustainable production, strict rules have been put in place to regulate the maximum amount of pigs that a farm can produce (regulated as a fixed number of animals per hectare). The majority (85%) of the total pork produced is exported from Denmark, driven by growing demand from Japan, China, the U.K., and Germany. The global chain of production and consumption of pork illustrates the multidimensional aspects that must be accounted for as we conceptualize land use (Table 5.3). In particular, it will be important to assess place-specifi c aspects for three dimensions of land: land use, ecosystem impacts, and socioeconomic drivers.

Another way to think about the land transformation chain is to account geographically for the consumption of virtual land: How does consumption of a product produced in a distant place take advantage of the land, water, and energy sources in that other location? This dependency can be described

Table 5.3 Land transformation chain: geographic decoupling of consumption and production.

Plant production or feed

Location of animal production or product transformation

Food demand or consumption

Land use: trends and determinants for land requirement

Ecosystem impact

Socioeconomic drivers (enabling and constraining conditions)

Accelerated pressure; possible expansion to marginal land; decoupling from local capacity or demand

Increasing pressure due to field expansion and intensification (e.g., biodiversity, habitat, water) Economy, technology, institutions

Stable conditions: land use not directly correlated to animal feed requirement but to local environment regulation Under pressure, e.g., groundwater pollution, lack of incentives to extensivation Economy, institutions, technology (transport, production)

Could set land free for other uses or other ecosystem services; decoupling of population and land

Probably relieve pressure on local environment

Culture, taste, economy, population as "virtual water consumption," "virtual energy consumption," or "virtual land consumption."

Our current conceptualization and accounting of land does not measure this land transformation chain. The concept of an ecological footprint is a first step toward resolving the total land requirements to sustain a community, but it only measures the aggregate land demand, not the geographic linkages between supply and demand. Only when we are able to account for the full land transformation chain will we be able to assess the sustainability of the land system. Consequently, global metrics for land need to be supplemented by information about the geographic patterns of—and linkages among—demand for feed or food and local land use.

A third limitation of the current conceptualization of land is the implication that human and natural areas are completely distinct. The allocation of land for different activities is distributed in a geographically disconnected way, where activities to meet human resource demands are disconnected from activities to protect nature (e.g., biodiversity and ecosystem services). Such duality decouples humans from the critical processes that give feedback signals of unsustainable land use. This has not always been the case. Historically, agricultural systems depended primarily upon local natural resources which, in turn, connected production directly with local environmental impact. This allowed for a tight correlation between production of animal products and the local "carrying capacity" of the land use system. In a globalized, geographically disconnected system, the human-environment duality encourages ever greater appropriation of land for human use, with the danger of few (or perhaps delayed) signals about unsustainable land use. In the example of the Danish pig production, a collapse in soybean production in Argentina may trigger a delayed price signal for pork in Japan.

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