Richard A. Birdsey

Forest carbon sinks in the northern hemisphere

There is general agreement that terrestrial systems in the Northern Hemisphere provide a significant sink for atmospheric CO2; however, estimates of the magnitude and distribution of this sink vary greatly. National forest inventories provide strong, measurement-based constraints on the magnitude of net forest carbon uptake. We brought together forest sector C budgets for Canada, the United States, Europe, Russia, and China that were derived from forest inventory information, allometric relationships, and supplementary data sets and models. Together, these suggest that northern forests and woodlands provided a total sink for 0.6–0.7 Pg of C per year (1 Pg = 1015 g) during the early 1990s, consisting of 0.21 Pg C/yr in living biomass, 0.08 Pg C/yr in forest products, 0.15 Pg C/yr in dead wood, and 0.13 Pg C/yr in the forest floor and soil organic matter. Estimates of changes in soil C pools have improved but remain the least certain terms of the budgets. Over 80% of the estimated sink occurred in one-third of the forest area, in temperate regions affected by fire suppression, agricultural abandonment, and plantation forestry. Growth in boreal regions was offset by fire and other disturbances that vary considerably from year to year. Comparison with atmospheric inversions suggests significant land C sinks may occur outside the forest sector.

A synthesis of current knowledge on forests and carbon storage in the United States

Using forests to mitigate climate change has gained much interest in science and policy discussions. We examine the evidence for carbon benefits, environmental and monetary costs, risks and trade-offs for a variety of activities in three general strategies: (1) land use change to increase forest area (afforestation) and avoid deforestation; (2) carbon management in existing forests; and (3) the use of wood as biomass energy, in place of other building materials, or in wood products for carbon storage. We found that many strategies can increase forest sector carbon mitigation above the current 162-256 Tg C/yr, and that many strategies have co-benefits such as biodiversity, water, and economic opportunities. Each strategy also has trade-offs, risks, and uncertainties including possible leakage, permanence, disturbances, and climate change effects. Because approximately 60% of the carbon lost through deforestation and harvesting from 1700 to 1935 has not yet been recovered and because some strategies store carbon in forest products or use biomass energy, the biological potential for forest sector carbon mitigation is large. Several studies suggest that using these strategies could offset as much as 10-20% of current U.S. fossil fuel emissions. To obtain such large offsets in the United States would require a combination of afforesting up to one-third of cropland or pastureland, using the equivalent of about one-half of the gross annual forest growth for biomass energy, or implementing more intensive management to increase forest growth on one-third of forestland. Such large offsets would require substantial trade-offs, such as lower agricultural production and non-carbon ecosystem services from forests. The effectiveness of activities could be diluted by negative leakage effects and increasing disturbance regimes. Because forest carbon loss contributes to increasing climate risk and because climate change may impede regeneration following disturbance, avoiding deforestation and promoting regeneration after disturbance should receive high priority as policy considerations. Policies to encourage programs or projects that influence forest carbon sequestration and offset fossil fuel emissions should also consider major items such as leakage, the cyclical nature of forest growth and regrowth, and the extensive demand for and movement of forest products globally, and other greenhouse gas effects, such as methane and nitrous oxide emissions, and recognize other environmental benefits of forests, such as biodiversity, nutrient management, and watershed protection. Activities that contribute to helping forests adapt to the effects of climate change, and which also complement forest carbon storage strategies, would be prudent.

BIOMASS AND NPP ESTIMATION FOR THE MID‐ATLANTIC REGION (USA) USING PLOT‐LEVEL FOREST INVENTORY DATA

As interest grows in quantification of global carbon cycles, process model predictions of forest biomass and net primary production (NPP) are being developed at an accelerating rate. Such models can provide useful predictions at large scales, but it has been difficult to evaluate their performance. Using the network of plots comprising the comprehensive and spatially extensive Forest Inventory and Analysis (FIA) data set collected and maintained by the USDA Forest Service, we applied methods typically used in field measurements to develop estimates of forest biomass and NPP for the mid-Atlantic region of the United States at a scale appropriate for comparison with model predictions. Plot-level and tree-level forest inventory data from a subset of plots were used together with species-specific biomass regression equations to calculate maximum current biomass and NPP values for the mid-Atlantic region. Estimates at the plot level were aggregated by forest type and to the 0.5° × 0.5° scale for analysis and comparison with process model predictions. Maximum current forest biomass averaged 248 and 200 Mg·ha−1·yr−1 in hardwood and softwood forest types, respectively; wood biomass increment averaged 559 and 460 g·m−2·yr−1 in hardwood and softwood forest types, respectively. Aggregated to the 0.5° × 0.5° scale, forest biomass ranged from 101 to 326 Mg/ha, while wood biomass increment ranged from 254 to 1050 g·m−2·yr−1. Biomass and NPP estimates for closed-canopy forests from this study were consistent with values reported in the literature but were as much as 50% lower than values reported for old-growth stands. NPP predictions from three process models were fairly consistent with the FIA-based estimates, but model predictions of biomass were higher than estimates from FIA data for the region. By describing upper and lower bounds on reasonable biomass and NPP values for closed-canopy forests, these FIA-derived estimates provide a foundation for model comparison and continued model development.

Recent rates of forest harvest and conversion in North America

Incorporating ecological disturbance into biogeochemical models is critical for estimating current and future carbon stocks and fluxes. In particular, anthropogenic disturbances, such as forest conversion and wood harvest, strongly affect forest carbon dynamics within North America. This paper summarizes recent (2000-2008) rates of extraction, including both conversion and harvest, derived from national forest inventories for North America (the United States, Canada, and Mexico). During the 2000s, 6.1 million ha/yr were affected by harvest, another 1.0 million ha/yr were converted to other land uses through gross deforestation, and 0.4 million ha/yr were degraded. Thus about 1.0% of North Americas forests experienced some form of anthropogenic disturbance each year. However, due to harvest recovery, afforestation, and reforestation, the total forest area on the continent has been roughly stable during the decade. On average, about 110 m3 of roundwood volume was extracted per hectare harvested across the continent. Patterns of extraction vary among the three countries, with U.S. and Canadian activity dominated by partial and clear-cut harvest, respectively, and activity in Mexico dominated by conversion (deforestation) for agriculture. Temporal trends in harvest and clearing may be affected by economic variables, technology, and forest policy decisions. While overall rates of extraction appear fairly stable in all three countries since the 1980s, harvest within the United States has shifted toward the southern United States and away from the Pacific Northwest.

Past and prospective carbon storage in United States forests

Global concern about increasing carbon dioxide concentrations in the atmosphere and the possible consequences of future climate changes have generated interest in understanding and quantifying the role of terrestrial ecosystem in the global carbon cycle. Historical changes in carbon storage in US forests have been estimated from periodic, comprehensive national inventories of forest resources. Since 1952, carbon stored on US timberland has increased by 38% or 8.8 × 1015 g, primarily in the East. This increase is consistent with recently reported trends in Europe and accounts for as much as 21% of a hypothesized carbon sink in Northern temperate forests. Projections of changes in carbon storage over long periods of time were made with a carbon budget model that has been integrated with econometric models of the forest sector. Carbon storage is expected to increase until 2040, but at a slower rate than at present.

Aboveground biomass distribution of US eastern hardwood forests and the use of large trees as an indicator of forest development

Abstract Past clearing and harvesting of the deciduous hardwood forests of eastern USA released large amounts of carbon dioxide into the atmosphere, but through recovery and regrowth these forests are now accumulating atmospheric carbon (C). This study examined quantities and distribution of aboveground biomass density (AGBD, Mg ha−1) of US eastern hardwood forests and assessed their biological potential for continued biomass accumulation in the future. Studies have shown that the presence of a large proportion of the AGBD of moist tropical forests in large diameter trees (> 70 cm diameter) is indicative of mature and undisturbed conditions. This relationship was tested as a criterion for the eastern US deciduous forests to assess their stage of recovery and maturity, and evaluate their potential for continued C storage. The approach was to compare AGBD and its distribution in large trees for old-growth forests derived from published studies and for oak-hickory and maple-beech-birch forests using the extensive US Forest Service Forest Inventory and Analysis (FIA) data base. Old-growth forests generally had AGBD of 220–260 Mg ha−1 with up to 30% in trees with diameter > 70 cm. In contrast, maximum AGBD for the FIA units was about 175–185 Mg ha−1 with 8%–10% in large trees. Most units, however, were below these maximum values, suggesting that the forests represented by the FIA inventory are in various stages of recovery from past disturbance. Biologically, therefore, they have the potential to accumulate significant quantities of additional biomass, if left unharvested, and thus storing atmospheric C into the future.

The potential of U.S. forest soils to sequester carbon and mitigate the greenhouse effect.

THE EXTENT, GENERAL CHARACTERISTICS, AND CARBON DYNAMICS OF U.S. FOREST SOILS Introduction and General Description of US Forests, J.M. Kimble, R.A. Birdsey, R. Lal, and L.S. Heath Current and Historical Trends in use, Management and Disturbance of United States Forest Lands, R.A. Birdsey and G.M. Lewis Carbon Trends in US Forest Lands: A Context for the Role of Soils in Forest Carbon Sequestration, L.S. Heath, J.E. Smith and R.A. Birdsey Quantifying the Organic Carbon Held in Forested Soils of the United States and Puerto Rico, M. Johnson and J. Kern Techniques to Measure and Strategies to Monitor Forest Soil Carbon, C. Palmer SOILS PROCESSES AND CARBON DYNAMICS Carbon Cycling in Forest Ecosystems with an Emphasis on Belowground Processes, K.S. Pregitzer Forest Soil Ecology and Soil Organic Carbon, S.J. Morris and E.A. Paul Global Change and Forest Soils, J. Hom Processes Affecting Carbon Storage in the Forest Floor and in Downed Woody Debris, W.S. Currie, R.D. Yanai, K.B. Piatek, C.E. Prescott, and C.L. Goodale Impacts of Natural Disturbance on Soil Carbon Dynamics in Forest Ecosystems, S.T. Overby, S.C. Hart, and D.G. Neary MANAGEMENT IMPACTS ON US FOREST SOILS Soil Erosion in Forest Ecosystems and Carbon Dynamics, W.J. Elliot Impact of Soil Restoration, Management, and Land Use History on Forest Soil Carbon, W. M. Post Fire and Fire Suppression Impacts on Forest Soil Carbon D. Page-Dumroese, M. Jurgensen and A. Harvey Soil Carbon Sequestration and Forest Management: Challenges and Opportunities, C.M. Hoover Management Impacts on Compaction in Forest Soils, R. Lal SPECIFIC FOREST ECOSYSTEMS Soil Carbon in Permafrost Dominated Boreal Forests, J. Hom Soil Carbon Distribution in High-Elevation Forests of the U.S.A., J.G. Bockheim Soil Carbon in Arid and Semiarid Forest Ecosystems, D.G. Neary, S.T. Overby and S.C. Hart Carbon Cycling in Wetland Forest Soils, C. Trettin and M.F. Jurgensen Carbon Storage in North American Agroforestry Systems, P.K. Nair and V.D. Nair Soil Carbon in Urban Forest Ecosystems, R. Pouyat, J. Russell-Anelli, I. Yesilonis, and P.M. Groffman Soil Organic Carbon in Tropical Forests of the United States of America, W.L. Silver, A.E. Lugo, and D. Farmer SYNTHESIS AND POLICY IMPLICATIONS The Potential of U.S. Forest Soils to Sequester Carbon, L.S. Heath, J.M. Kimble, R.A. Birdsey, and R. Lal Economic Analysis of Soil Carbon in Afforestation and Forest Management Decisions, B. Sohngen, R. Alig, and Suk-won Choi Research and Development Priorities for Carbon Sequestration in Forest Soils, R. Lal

Relationships between net primary productivity and forest stand age in U.S. forests

[1] Net primary productivity (NPP) is a key flux in the terrestrial ecosystem carbon balance, as it summarizes the autotrophic input into the system. Forest NPP varies predictably with stand age, and quantitative information on the NPP-age relationship for different regions and forest types is therefore fundamentally important for forest carbon cycle modeling. We used four terms to calculate NPP: annual accumulation of live biomass, annual mortality of aboveground and belowground biomass, foliage turnover to soil, and fine root turnover in soil. For U.S. forests the first two terms can be reliably estimated from the Forest Inventory and Analysis (FIA) data. Although the last two terms make up more than 50% of total NPP, direct estimates of these fluxes are highly uncertain due to limited availability of empirical relationships between aboveground biomass and foliage or fine root biomass. To resolve this problem, we developed a new approach using maps of leaf area index (LAI) and forest age at 1 km resolution to derive LAI-age relationships for 18 major forest type groups in the USA. These relationships were then used to derive foliage turnover estimates using species-specific trait data for leaf specific area and longevity. These turnover estimates were also used to derive the fine root turnover based on reliable relationships between fine root and foliage turnover. This combination of FIA data, remote sensing, and plant trait information allows for the first empirical and reliable NPP-age relationships for different forest types in the USA. The relationships show a general temporal pattern of rapid increase in NPP in the young ages of forest type groups, peak growth in the middle ages, and slow decline in the mature ages. The predicted patterns are influenced by climate conditions and can be affected by forest management. These relationships were further generalized to three major forest biomes for use by continentalscale carbon cycle models in conjunction with remotely sensed land cover types. Citation: He, L., J. M. Chen, Y. Pan, R. Birdsey, and J. Kattge (2012), Relationships between net primary productivity and forest stand age in U.S. forests, Global Biogeochem. Cycles, 26, GB3009, doi:10.1029/2010GB003942.

Costs of creating carbon sinks in the U.S.

Abstract New models of the dynamic patterns of carbon uptake by forest ecosystems allow improvements in the estimation of the costs of carbon sequestration in the U.S. The preliminary results of an effort to update an earlier study indicate that conversion of environmentally sensitive and economically marginal cropland and pastureland in the U.S. could offset as much as 25% of current U.S. emissions at costs of

Attributing carbon changes in conterminous U.S. forests to disturbance and non-disturbance factors from 1901 to 2010

US 8–60 per short ton.