This section discusses the potential associated impacts-positive and negative-of LULUCF activities and projects as they relate to several dimensions of environmental quality: biodiversity, soil quality, soil erosion, water quality and quantity, acidification, and climate feedbacks.
Biodiversity refers to the variability among living organisms and the ecological complexes of which they are part. Biodiversity includes diversity within species (genetic diversity), diversity between species, and diversity of ecosystems (Glowka et al., 1994). The goal of biodiversity protection is not met by simply maintaining the number of species but by ensuring that no species, genes, or ecosystems-especially those that are endemic, rare, or threatened-are lost. Some of these benefits are most prominent in tropical and subtropical forests: Tropical forests harbor an estimated 50-70 percent of all species. Anticipated climate change will greatly change the environments for many species, with the likely result that many species with restricted distributions-especially slow-growing, late-successional species or those with restricted seed dispersal-may be lost (Kirschbaum et al., 1996).
The diversity of life forms and their living environments generally decreases along the spectrum of land use from primary forest to regenerated forest, plantation forest, and agricultural land (e.g., Marshall and Swaine, 1992; Whitmore and Sayer, 1992; Michon and de Foresta, 1995; Canaday, 1996). Conversely, biodiversity increases when degraded lands are forested, and it is usually assumed that biodiversity increases when agricultural land is converted to most types of forest.
Agricultural lands can also be managed to be species-rich, however; in the tropics, biodiversity may sometimes be greater in a mixed landscape of primary forest, regenerated forest, plantations, and agricultural lands than in primary forest alone (Lawton et al., 1998). Afforestation can increase diversity only where it replaces land cover that is species-poor; in some places, afforestation can threaten valuable non-forest species and habitats.
Biodiversity benefits to society derive from the fundamental contribution of biodiversity to ecosystem function, the provision of diverse goods and services, and aesthetic and spiritual factors. These benefits are enjoyed locally and globally and are experienced by individuals directly and indirectly. Clearly, not all of these biodiversity benefits can be well quantified or monetized. Even if these values could be derived in principle (and there is much debate among economists, ecologists, philosophers, and others about whether they can be), the methods for estimating them are limited, especially for the more intangible services that biodiversity provides (Norton, 1988; Stirling, 1993). Although various indirect methods have been developed to estimate biodiversity's value in monetary terms, no single method is capable of producing a valid monetary equivalent to each of the aspects of biodiversity value (Price, 1997). Although the monetary value of biodiversity is recognized as being very high (Pearce and Moran, 1994; Costanza et al., 1997; Pimentel et al., 1997a), the willingness of the world at large to pay for it limits how much of this value can be translated into a monetary flow (Fearnside, 1999a). That willingness to pay generally has been increasing and may increase substantially in the future.
Existence value-the intrinsic value of species and natural ecosystems to human society, independent of "utilitarian" benefits-is an area in which some progress has been made toward quantification for decisionmaking purposes (Attfield, 1998). This class of value accrues mostly to populations who are either very close to the forest-such as indigenous communities-or those who are far removed from it, such as urban dwellers elsewhere.
Estimating biodiversity benefits is more tractable when those benefits are tied to the provision of commercial goods and services, such as non-timber forest products (Peters et al., 1989; V�squez and Gentry, 1989; Whitehead and Godoy, 1991; Hecht, 1992; Richards, 1993; Grimes et al., 1994; Pimentel et al., 1997b). Local benefits also accrue from the stock of genetic material of plants and animals needed to produce a degree of adaptability to forest management and to agricultural systems that sacrifice biodiversity in nearby unprotected areas (Myers, 1989). The stock of useful chemical compounds and genetic materials for other than local use represents an investment in protecting future generations (including those in distant places) from the consequences of the absence of that material when it is needed one day. This factor is referred to as the "prospecting value" of genetic resources. A medicinal use, such as a cure for a disease, is worth more to society than the profits from selling the drug. This value also includes the value to consumers of the drug whose lives are saved or otherwise improved.
Several studies have shown substantial potential for identifying chemical models for pharmacological products based on tropical forest plants (Kaplan and Gottlieb, 1990; Elisabetsky and Shanley, 1994; Cordell, 1995). An estimate of the opportunity cost for the sale of medicinal products derived from rainforests in Mexico arrived at a figure of US$6.4 ha-1 yr-1, with a range from US$1-90 ha-1 yr-1 (Adger et al., 1995). Simpson et al. (1996), however, estimate somewhat lower values for willingness to pay for the medicinal benefits of biodiversity. Their estimates range from $0.20-20.63 ha-1 lump sum for incremental increases in land preserved in 18 biodiversity hot spots throughout the world.
Any major land-use change will change the types of habitats and species, irrespective of any change in diversity; the most serious negative impacts generally would result from deforestation of primary forest, especially in the tropics. Ongoing deforestation reduces the diversity of life forms by causing the extinction of organisms and the loss of genetic diversity in the remaining ones. Hence, with regard to biodiversity, the most beneficial outcomes generally can be achieved where deforestation can be halted or slowed.
Studies have systematically identified forest ecoregions throughout the world that are known to be both biologically important (containing an assemblage of species that is unusually rich, globally rare, or unique to that region) and under considerable threat of further loss or degradation (Dinerstein et al., 1995; Olson and Dinerstein, 1998). Any LULUCF climate mitigation project that slows deforestation or degradation will help conserve biodiversity.
Protecting the most threatened ecosystems does not always provide the greatest carbon benefits, however. In Brazil, for example, the least well-protected and most threatened types of forest are along the southern boundary of Amazonia, where reserve establishment is relatively expensive and forests contain less biomass than in central Amazonia (Fearnside and Ferraz, 1995).
On the other hand, tradeoffs between carbon storage and maintenance of biodiversity can also occur in the creation of large areas of productive managed forest, especially monocultures of exotic species. High productivity demands high light interception, which suppresses ground flora and limits other life forms (Hill and Wallace, 1989). Rapid forest establishment means that there are no long periods of recovery that provide habitats following natural disturbance (Rochelle and Bunnell, 1979). Harvesting at the time, which maximizes timber yield, prevents the development of special habitats that occur in old-growth forests (Bull and Meslow, 1977), and plantations of single tree species are likely to have more limited and particular types of fauna and flora than natural forest stands (Kennedy and Southwood, 1984). There are, however, management options to address the tradeoffs between production and biodiversity-such as adopting longer rotation times; altering felling unit sizes; altering edge lengths; prolonging rotation lengths; creating a multi-aged patchwork of stands; minimizing chemical inputs; reducing or eliminating measures to clear understory vegetation; or using mixed species plantings, including native species (e.g., Allen et al., 1995a,b; Da Silva et al., 1995).
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