90 | North America and Europe (NAE) Report

fish ponds, trout farms and some seawater closed systems, avoid many of the problems of caged aquaculture as the possibility of escape of the livestock or transmission of dis­eases to native populations is greatly reduced. However, the effluent from such systems may be rich in organic matter and plant nutrients. Unrestricted discharge of these waters could impair receiving water quality. Use of systems that used the discharge from farm ponds to directly irrigate and fertilize farm fields, or use additional ponds to grow algae, which in turn is used as a fertilizer or livestock feed supplement, can eliminate or reduce the impacts on receiving waters.
     Filter feeding molluscs (clams, mussels, oysters, scal­lops) in aquaculture rely on natural suspended particulates (i.e., phytoplankton and detritus) rather than external food sources. Such systems do not add new materials to the eco­system and are unlikely to create the eutrophication prob­lems of finfish caged aquaculture. However, these systems may redistribute organic matter and concentrate organic materials in sediments below the structures holding the cul­tured organisms.
     Similarly, seaweed culture does not rely on external inputs and therefore does not have the eutrophication im­pacts that can occur in caged, externally fed organisms. In­deed, it has been suggested that carefully placed mollusk or seaweed culture, used in an integrated system with caged culture, could help cleanup the organic residue and algal growth promoted by externally fed aquaculture (Lindahl et al., 2005; Troell et al., 2005).

3.1.4 Environmental consequences of changes in for­est management
Forests cover an appreciable proportion of the land surface of the NAE, especially in parts of N. America and in Rus­sia, so changes in forest management have the potential to have appreciable environmental impacts. Forests provide environmental benefits of wildlife habitat, plant and animal biodiversity, timber, provision of clean water and carbon storage. High-quality riparian areas trap sediments, slow runoff, provide habitat for wildlife, fish and plants (USDA-USFS, 1999).
     The quality of forests may be affected by clearing, but also can be damaged by air pollution, e.g., acid rain and ground-level ozone (USDA-USFS, 1999). Forests may also be damaged by fire, invasive species and unmanaged rec­reation (Bosworth, 2004). In addition, nitrogen deposition from the atmosphere may potentially cause a shift in com­position of some forests. The USDA Forest Service has also identified how ozone damages trees and has screened tree varieties for those less susceptible to this gas. Studies are ongoing to identify ozone-sensitive trees in areas of ozone exposure, increasing our understanding of how to manage forest resources (USDA-USFS, 1999).
     In Europe, the replacement in the last century of mixed aged stands of often deciduous woodlands with uniform age conifer plantations has had negative effects on biodiversity, especially ground flora and mammalian fauna and some­times on soils and surface waters (Hartley, 2002; Humphrey et al., 2002; Spiecker, 2003; MA, 2005). Bird populations may also be adversely affected but in some cases, conver­sion and intensive management has boosted populations of birds and some mammals that were previously rare in pri-


mary forest (such as crossbills (Loxia curvirostra) red squir­rels and pine martens) in Scotland, where 90% of woods are plantations (Marquiss and Rae, 1994). About 40% of the hundred European "priority" forest bird species are in unfavorable conservation status, mainly due to declines in old-growth forest (BirdLife International, 2007). Conifer­ous plantations also appear to increase the acidity of pre­cipitation falling on them, leading to reductions in pH of streams, rivers and lakes within forested areas (Spiecker, 2003). Although the area of forested land in Europe is in­creasing, most of the increase is made up of plantations and secondary woodland and this does not necessarily offset the reductions in flora and fauna caused by conversion of natu­ral forests to intensively managed plantations. Awareness of the negative impacts of uniform age conifer plantations has resulted in much debate in Europe as to the economic viability of replacing them with mixed species stands, with both conifer and deciduous species (Spiecker, 2003). Despite declines in natural forest quantity and quality in W. and some E. Europe countries, European forests remain one of the most important refuges for wildlife on the continent. Additionally, the increase in forested timber volume within the NAE increases carbon sequestration and is of value in reducing atmospheric levels of CO2
     Environmental concerns about forestry have resulted in changes in approaches to tree production and to manage­ment in the USA since 1970. In the 1970s public concern in the USA about the effect of current clear-felling and re­forestation practices led to the 1976 National Forest Man­agement Act (NFMA). One of the important developments following the passage of this Act was the establishment of the Long-Term Soil Productivity (LTSP) research program (Williams, 2000) to explore and reduce the environmental effects of forestry practices (e.g., see Powers et al., 2005). Changes in practices arising from AKST have had some suc­cess in the last 30 years in ameliorating some of the negative environmental effects of forestry in the USA. However it must also be noted that new technologies developed since the second world war allow faster and more efficient har­vests and access to timber in areas previously considered too fragile for harvest, thus expanding the potential managed forest areas.

3.1.5 Overall environmental consequences of changes in the agricultural industry
The previous sections of this chapter have highlighted the major issues associated with specific changes in crop and animal production and forestry. However there are also is­sues that transcend these individual components, as there are environmental consequences arising from overall changes in agriculture and which cannot easily be attributed to indi­vidual components. Two issues are highlighted here, the im­pacts of changes in the intensity of agricultural production on the natural ecosystem and the issue of "food miles". Overall environmental consequences of increased intensity of agriculture
As the dominant land use throughout much of Europe, ag­riculture (including forestry), has a huge footprint on the overall ecosystem, especially in intensively farmed countries such as France, The Netherlands and UK. There have been