The loss of biodiversity resulting from human activities is thought to be one of the most pressing problems of global environmental change. Nevertheless, our understanding of biodiversity loss is hampered by significant knowledge gaps. At present, there is not even an agreement on how many species inhabit the earth and how fast biological diversity is being depleted (Groombridge 1992).
Slowing down the rate of human-caused biodiversity loss requires indicators according to the drivers, pressures, states, impacts, and responses scheme (EEA 2003); that is, we need to know which socioeconomic processes result in which pressures on biodiversity, how biodiversity changes, what impacts these changes have on society, and which measures are taken to mitigate pressures or to cope with impacts. Each of these indicator types has specific functions: Indicators of socioeconomic drivers and pressures are needed to support policies to change socioeconomic trajectories in a more biodiversity-friendly direction, and state indicators are needed to monitor changes in biodiversity (Chapter 16, this volume). Response indicators monitor conservation measures, and impact indicators judge the socioeconomic significance of biodiversity changes. This chapter focuses on pressure indicators.
Whereas a host of maps, data, or assessments are needed to support specific conservation plans at local levels (an issue not discussed here), a limited number of valid aggregate pressure indicators is needed to support the development of large-scale (e.g., national, global) strategies to achieve social and economic progress while decreasing pressures on biodiversity at the same time. To validate such indicators, it has to be shown that they are unambiguously related to biodiversity loss, and they reliably represent defined socioeconomic activities. If we simply regard gross domestic product (GDP) or population as indirect pressures on biodiversity, we remain in a deadlock where we are forced to choose between adequately nourishing the growing world population or conserving biodiversity, or between economic development needed to combat poverty and biodiversity protection. By contrast, sustainable development should reconcile food production, economic development, and biodiversity conservation, and developing such strategies requires aggregate pressure indicators that are currently lacking (Eurostat 1999).
This chapter discusses theoretical considerations and the available empirical evidence (which unfortunately is limited to only one component of biodiversity, species richness) suggesting that human appropriation of net primary production (HANPP) may be such an indicator. Of course, HANPP will have to be complemented by other indicators. Some of them may be closely related (e.g., indicators that evaluate human interference with hydrological cycles; Postel et al. 1996); others may focus on different system qualities.
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