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United Nations Environment Programme
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Freshwater Management Series No. 7

Phytotechnologies

A Technical Approach in Environmental Management

II. Global Issues Requiring Innovative Sollutions >

E. Climate Change

The United Nations Framework Convention on Climate Change (UNFCCC), adopted in 1992, states that: “Each Party shall limit its anthropogenic emissions of greenhouse gases and protect and enhance its greenhouse gas sinks and reservoirs”. Under the UNFCCC, a “sink” is defined as “any process, activity or mechanism which removes a greenhouse gas, an aerosol, or a precursor of a greenhouse gas from the atmosphere.” Currently, photosynthesis, a natural biological process, is the only process considered by the UNFCCC to act as a sink by removing carbon dioxide from the atmosphere. However, it is also widely recognized that anthropogenic land uses and land use changes can alter the magnitude and rate of natural exchanges of greenhouse gases. Due to the dominating influence of natural forests and large areas in agriculture, the issue of carbon sinks in relation to land-use, land-use change and forestry is of particular interest.

Aerial view of swirling white clouds

Humans interact with land in many different ways and the linkages between humans and plants in relation to climate change are multiple, centering on forests, both boreal and tropical, as well as agricultural lands and wetlands. Global forests fix a high proportion of atmospheric carbon dioxide. Each forest ecosystem has its own profile, depending on its state of succession, climatic factors and expos ure to natural and human disturbances.

Although the primary source of anthropogenic carbon dioxide emissions is the use of fossil fuels, deforestation contributes significantly to the net increase of atmospheric carbon dioxide. Deforestation can be defined as the conversion of forested land to other land-use. This includes forest conversion for permanent land-use changes such as agriculture, as well as the development of permanent infrastructure, such as highways. Some of the other factors affecting GHG emissions include the harvest and use of wood commodities, and the establishment and operation of forest plantations. Forests also contain a high proportion of the world’s biodiversity and as these areas are deforested, biodiversity is threatened. Policies to reduce deforestation are an important element of an overall strategy to address both global climate change and biodiversity. Two important areas of activity are afforestation and reforestation.

Afforestation is the planting of new forests on lands which, historically, have not contained forests. One of the principal challenges of afforestation efforts is the difficulty of convincing individual landowners to allow their marginal agricultural and other land to become forested land. Afforestation is likely to proceed slowly at first, as programs and policies are implemented, financing mechanisms are established, landowners and others learn about opportunities, technical advice is provided, rules for carbon accounting are developed and seedlings are made ava ilable. Focusing on achieving goals which go beyond just carbon sequestration, such as environmental and land management goals, is likely to be the most successful approach to afforestation over the longer term.

Reforestation is the planting of forests on lands which have, historically, previously contained forests but which have been converted to some other use. Two elements of regeneration strategies that could increase carbon sequestration potential are species selection and density management. While current research is aimed at maximizing the volumes of the commercial harvest, some results have shown that significant biomass gains can be achieved by modifying planting or spacing regimes. In addition to species selection and density management, increased planting instead of natural regeneration and seeding after harvesting can also increase carbon sequestration.

Another important climate change mitigation strategy to realize the potential of agricultural soil carbon sinks, including conservation practices on croplands (i.e., reduced or no tillage and reduced summerfallow), pasture management, conversion of marginal croplands to perennial grass and conservation of wetlands and riparian areas. Agricultural soil sequestration could offer crop producers greater revenue, and potentially lower input costs resulting from lower fuel use, as well as more efficient use of fertilizers. Encouragement of conservation practices on cropland, including no till and reduction in conventional summerfallow is potentially one of the more cost-effective strategies. The overall impact of agricultural soils conservation practices on the environment is a healthier, more productive soil that is less subject to wind or water erosion, and a more resilient, environmentally sustainable agro-ecosystem.

The restoration of wetland basins through re-establishment of aquatic vegetation, as well as soil carbon restoration in riparian zones and uplands that may be cultivated, is another important element of an integrated strategy to address climate change. Attributes of wetlands, which render them net sinks, include:

high primary productivity ensuring abundant organic carbon available for sequestration,
reduced decomposition due to the anaerobic nature of wetland sediments and colder northern climates,
reduced CH4 emissions due to CH4 oxidation in the aerobic environment of algae and emergent vegetation,
low nitrous oxide emissions due to continually water-logged soils and low nitrate levels in many wetlands.

The application of phytotechnologies in the management of forests, agricultural land and wetlands represents an important strategy for climate change mitigation and adaptation. However, the optimum use of phytotechnologies leading to the establishment of more resilient ecosystems requires a better understanding of the physiology of plant species under different environmental conditions, as well as an understanding of the role of plant biomass and biodiversity in relation to energy flows and ecohydrology.

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