Robert K. Dixon

Estimating the global potential of forest and agroforest management practices to sequester carbon

Forests play a prominent role in the global C cycle. Occupying one-third of the earths land area, forest vegetation and soils contain about 60% of the total terrestrial C. Forest biomass productivity can be enhanced by management practices, which suggests that, by this means, forests could store more C globally and thereby slow the increase in atmospheric CO2. The question is how much C can be sequestered by forest and agroforest management practices. To address the question, a global database of information was compiled to assess quantitatively the potential of forestry practices to sequester C. The database presently has information for 94 forested nations that represent the boreal, temperate and tropical latitudes. Results indicate that the most promising management practices are reforestation in the temperate and tropical latitudes, afforestation in the temperate regions, and agroforestry and natural reforestation in the tropics. Across all practices, the median of the mean C storage values for the boreal latitudes is 16 tCha[−1 (n=46) while in the temperate and tropical latitudes the median values are 71 tCha−1 (n=401) and 66 tCha−1 (n=170), respectively. Preliminary projections are that if these practices were implemented on 0.6 to 1.2×109 ha of available land over a 50-yr period, approximately 50 to 100 GtC could be sequestered.

Integrated Land-Use Systems: Assessment of Promising Agroforest and Alternative Land-Use Practices to Enhance Carbon Conservation and Sequestration

Degraded or sub-standard soils and marginal lands occupy a significant proportion of boreal, temperate and tropical biomes. Management of these lands with a wide range of existing, site-specific, integrated, agroforest systems represents a significant global opportunity to reduce the accumulation of greenhouse gases in the atmosphere. Establishment of extensive agricultural, agroforest, and alternative land-use systems on marginal or degraded lands could sequester 0.82–2.2 Pg carbon (C) per year, globally, over a 50-year time-frame. Moreover, slowing soil degradation by alternative grassland management and by impeding desertification could conserve up to 0.5–1.5 Pg C annually. A global analysis of biologic and economic data from 94 nations representing diverse climatic and edaphic conditions reveals a range of integrated land-use systems which could be used to establish and manage vegetation on marginal or degraded lands. Promising land-use systems and practices identified to conserve and temporarily store C include agroforestry systems, fuelwood and fiber plantations, bioreserves, intercropping systems, and shelterbelts/windbreaks. For example, successful establishment of low-intensity agroforestry systems can store up to 70 Mg C/ha in boreal, temperate and tropical ecoregions. The mean initial cost of soil rehabilitation and revegetation ranges from

The global terrestrial carbon cycle

500–3,000/ha for the 94 nations surveyed. Natural regeneration of woody vegetation or agro-afforestation establishment costs were less than

Forest Sector Carbon Offset Projects: Near-Term Opportunities to Mitigate Greenhouse Gas Emissions

1000/ha in temperate and tropical regions. The costs of C sequestration in soil and vegetation systems range from

Forest Management and Carbon Storage: An Analysis of 12 Key Forest Nations

1-69/Mg C, which compares favorably with other options to reduce greenhouse gas emissions to the atmosphere. Although agroforestry system projects were recently established to conserve and sequester C in Guatemala and Malaysia, constraints to wide-spread implementation include social conditions (demographic factors, land tenure issues, market conditions, lack of infrastructure), economic obstacles (difficulty of demonstrating benefits of alternative systems, capital requirements, lack of financial incentives) and, ecologic considerations (limited knowledge of impacts and sustainability of some systems).

Conservation and sequestration of carbon: The potential of forest and agroforest management practices☆

There is great uncertainty with regard to the future role of the terrestrial biosphere in the global carbon cycle. The uncertainty arises from both an inadequate understanding of current pools and fluxes as well as the potential effects of rising atmospheric concentrations of CO2 on natural ecosystems. Despite these limitations, a number of studies have estimated current and future patterns of terrestrial carbon storage. Future estimates focus on the effects of a climate change associated with a doubled atmospheric concentration of CO2. Available models for examining the dynamics of terrestrial carbon storage and the potential role of forest management and landuse practices on carbon conservation and sequestration are discussed.

Global forest systems: An uncertain response to atmospheric pollutants and global climate change?

The Framework Convention on Climate Change separately recognizes sources and sinks of greenhouse gases and provides incentives to establish C offset projects to help meet the goal of stabilizing emissions. Forest systems provide multiple opportunities to offset or stabilize greenhouse emissions through a reduction in deforestation (C sources), expansion of existing forests (CO2 sinks) or production of biofuels (offset fossil fuel combustion). Attributes and dimensions of eight forest-sector C offset projects, established over the past three years, were examined. The projects, mostly established or sponsored by US or European electric utilities, propose to conserve/sequester over 30 x 106 Mg C in forest systems at an initial cost of

Monitoring global change: Comparison of forest cover estimates using remote sensing and inventory approaches.

1 to 30 Mg C. Given the relative novelty and complexity of forest sector C offset projects, a number of biogeochemical, institutional, socio-economic, monitoring, and regulatory issues merit analysis before the long-term potential and cost effectiveness of this greenhouse gas stabilization approach can be determined.

Can the Terrestrial Biosphere Be Managed to Conserve and Sequester Carbon

Forests of the world sequester and conserve more C than all other terrestrial ecosystems and account for 90% of the annual C flux between the atmosphere and the Earths land surface. Preliminary estimates indicate that forest and agroforest management practices throughout the world can enhance the capability of forests to sequester C and reduce accumulation of greenhouse gases in the atmosphere. Yet of the 3600 × 106 ha of forests in the world today, only about 10% (350×106 ha) are actively managed. The impetus to expand lands managed for forestry or agroforestry purposes lies primarily with nations having forest resources. In late 1990, an assessment was initiated to evaluate the biological potential and initial site costs of managed forest and agroforest systems to sequester C. Within the assessment, 12 key forested nations were the focus of a special analysis: Argentina, Australia, Brazil, Canada, China, Germany, India, Malaysia, Mexico, South Africa, former USSR, and USA. These nations contain 59% of the worlds natural forests and are representative of the worlds boreal, temperate, and tropical forest biomes. Assessment results indicate that though the worlds forests are contained in 138 nations, a subset of key nations, such as the 12 selected for this analysis, can significantly contribute to the global capability to sequester C through managed tree crops. Collectively, the 12 nations are estimated to have the potential to store 25.7 Pg C, once expanded levels of practices such as reforestation, afforestation, natural regeneration and agroforestry are implemented and maintained. Initial site costs based upon establishment costs for management practices are less than US

Forest fires in Russia: carbon dioxide emissions to the atmosphere

33/Mg C.