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Emissions of ozone precursors are expected to multiply the next 20 years in China, and the levels of photo-oxidants may increase substantially. Increased surface ozone gives cause for concern regarding the prospects for Chinese agricultural production. We show that crop production may be substantially reduced in the future due to elevated ozone concentrations, and that productivity may already be affected for some crops. However, crop-yield loss estimates obtained by using alternative exposure-response functions vary substantially. Spring wheat, soybean, and corn may be especially vulnerable to future ozone increases, due to a likely concurrence of peak levels of ozone and the growth season of these crops.
The World Heritage Convention has been ratified by 158 countries and provides an international legal regime for the conservation of sites of global cultural or natural value. There are 33 tropical forest sites listed under the convention, mainly for their global biodiversity value. They constitute an elite set of biodiversity sites covering approximately 2.5% of the world's closed tropical forests and making a significant contribution to the conservation of the world's terrestrial biodiversity. A range of international initiatives will eventually provide a framework for better conservation and sustainable management of forests worldwide, but the World Heritage Convention provides an existing mechanism which could quickly be mobilized to safeguard the most important forests. In the past sites were selected for listing under the convention if they were perceived to have minimal human impact. However, all forests are modified by humans and we contend that modification need not be inconsistent with the maintenance of global biodiversity values. The convention could have greater impact if it addressed more directly the reality of the ubiquitous human modification of forests. This could be achieved through use of more adaptive forms of management based on objective criteria and indicators to define tolerance of change and trigger management responses to achieve desired biodiversity outcomes. We conclude that an optimal list of world heritage tropical forest sites might include up to 100 sites or clusters of sites and that such a network of sites could effectively protect a high proportion of the world's forest biodiversity. The present rate of attrition of the world's tropical forests suggests the need for urgent international action to focus on a set of priority sites and the World Heritage Conservation could provide the best international framework for such action.
All harvesting of biomass results in a loss of plant nutrients from the soil. The impact of this loss on forest productivity can be determined only if the total amounts of plant nutrients in logs, other biomass and soil are known. In investigations of tropical rainforest ecosystems the total analysis of calcium is common with regard to logs and other biomass, whereas for soils only the content of exchangeable calcium has been determined. This study, involving a calcium-poor bedrock area in Sabah, Malaysia, shows that the contents of total calcium in the soil can be estimated from figures of exchangeable calcium. In the state of Sabah, these estimated amounts were lower in 19 out of 115 soil profiles compared with the amount measured at our research area at Mendolong in Sabah where a sustainable forestry is not possible with the present rotation period without compensating for the harvest-related loss of calcium.
In 1991, in order to assess changes in soil acidity, we resampled the mineral soil from 95 plots in beech forests distributed throughout northeastern France, ca. 20 years after a first sampling in 1970–1973. Changes between the two sampling dates were more conspicuous for acidic soils than for mesotrophic or calcareous soils. We observed a significant decrease in base saturation, exchangeable calcium, magnesium, and potassium in the whole profile of the acidic soils. Median cation losses calculated for these soils down to a depth of 80 cm were 18.7 kg ha−1 yr−1 for calcium, 2.7 kg ha−1 yr−1 for magnesium, and 2.4 kg ha−1 yr−1 for potassium. This loss was not reflected by changes in soil pH (measured in water extracts). The intensity of the cation losses and the analysis of the pollution climate over the last 20 years suggest that atmospheric deposition could have contributed to the observed changes.
Historical accounts of the Inca indicate that they greatly valued trees and practiced planting to fulfil their needs for fuel and timber. These records are evaluated in the light of palaeoecological and archaeological evidence suggesting a dramatic increase in arboreal taxa from c. AD 1100 during a period of significant global temperature increase. This natural vegetation response to improving environmental conditions may have stimulated management;it is suggested that agroforestry has a long tradition in the Andes. With the arrival of the Spanish, in the 1530s, land management practices changed and forest resources became increasingly overexploited. A multidisciplinary approach may provide important lessons from the past for modern policy makers in Peru. Widespread planting ofEucalyptus may not be an appropriate solution. Land restoration projects should take account of natural diversity and utilize a range of native species. This is relevant in view of the current period of rising temperatures, and may help to alleviate both soil erosion and rural poverty.
The distributions of both the organismal and ecological diversity of Peru were evaluated through cartographic analyses in relationship to Peru's national system of protected areas. Also identified and mapped were areas so poorly known that they represent conservation information gaps, areas that cannot currently be evaluated, but which should not be overlooked. These methods revealed that the protected area system in Peru did not adequately protect either organismal or ecological diversity. In the short term, inclusion of unprotected priority areas in the national system is the best way to improve biological conservation. Over long time periods, it is also important to make decisions about the priority of areas that are information gaps. This study provides a useful point of comparison with other countries that are at different stages in the task of assembling biodiversity information. It was clear that i) the identified priority areas were important for national-level planning; ii) the drier and nonforested ecosystems seldom have been included in conservation efforts; iii) because degradation processes will constantly change, the conservation status of a particular area will also change and should not be confounded in the setting of priorities with the value of the biological diversity present; and iv) the identification of information gaps is the most transparent method for keeping decision-makers advised as to the limits of scientific knowledge on the distribution of biological diversity.
The occurrences of drifting algal masses were mapped in the Archipelago Sea, Northern Baltic Sea, during the summers of 1996–1997 using an UW-video and SCUBA-diving. The study covers depths from the shore down to 50 meters. The algal masses were described and classified according to the thickness of the mass and possible occurrence of anoxia (smell of hydrogen sulfide, black colored sediment), i.e. indicators of the masses potential different ecological impacts. Three different types of drifting algal masses were distinguished: cover, mat, and mattress. The succession of the masses was studied during one growing season. First, the algae aggregate on the sea floor as a thin cover. Later they start to drift downwards along the sloping bottom, developing into partly anaerobic mats and further into totally anaerobic mattresses. The phenomenon was most severe in the outer archipelago of the SE corner of the study area. Factors contributing to the growth of ephemeral algae, which result in drifting algal mats, include high nutrient loading, good water transparency, and appropriate bottom substrate. During the study we became convinced that the UW-video system is a practical tool for studying underwater loose-lying algal masses.
To adequately manage the fragile and changing environments of semiarid regions it is essential to disentangle human from climate or other environmental impacts over longer timescales than human memory. We investigated sediment cores from Salada Chiprana, a saline lake in the central Ebro basin in Spain, using pollen, charcoal, sedimentological, geochemical and radiometric dating techniques. The sequence indicates a rapid evolution from an ephemeral playa lake during the Late Holocene to a permanent saline lake a few centuries ago. The limnological evolution correlates with changes in agricultural practices and provides evidence of the strong impact of irrigation on the lake's hydrological balance from the XVth century. The work demonstrates that the Salada Chiprana, the only permanent, relatively deep, hypersaline lake in Spain has been created by a long history of human interaction with the landscape.
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