DINÂMICA DE USO E COBERTURA DA TERRA

BIBLIOGRAFIA û (http://www.dpi.inpe.br/dalves/sre40301.html)

J. Aber & J. Melillo, 1991

Terrestrial Ecosystems, (Philadelphia: Saunders College Publishings).

Adams, J.M. , Faure, H., 1998

A new estimate of changing carbon storage on land since the last glacial maximum, based on global ecosystem reconstruction.

Global and Planetary Change 16-17 (1998) 3-24

Abstract: A review of global land vegetation 18,000, 8000, and 5000 "C years B.P. allowed map reconstructions of past ecosystem distribution. By collecting soil and vegetation carbon storage data from the ecological literature, the map reconstructions were then used to estimate the total organic carbon storage on land at each of these time slices. Our best estimate suggests that there was an extremely large increase in land organic carbon storage, of around 1500 Gt (with extreme outer error limits for the increase placed at around 900 and 1900 Gt, respectively) between the Last Glacial Maximum (LGM) and the early-to-mid Holocene. It seems that the world's terrestrial carbon reservoirs more than doubled in size between full-glacial and full-interglacial conditions, due to a great increase in the areas of forest and other carbon-rich ecosystems. Although there are many uncertainties in such calculations, comparing them to methods used in other published estimates, we suggest that the present estimate may represent an overall improvement in accuracy. Apparent problems in previous studies include the use of relatively few data points and a limited range of types of palaeoenvironmental evidence, the unselective use of carbon storage data from anthropogenically modified ecosystems, and the assignment of an anomalously high carbon storage to the LGM 'steppe-tundra' ecosystem.

Alves, D. S., Skole, D. L., 1996

Characterizing land cover dynamics using multi-temporal imagery

INT. J. REMOTE SENSING, 1996, VOL. 17, 835-839

Abstract: An analysis of land cover changes was performed using a time-series of five SPOT HRV images for an area of the State of RondŸnia (western Brazilian Amazon) from 1986 to 1992. The total deforested area and the fraction of land abandoned to secondary vegetation were determined by means of image classification and Geographical Information System (GIS) techniques. Areas deforested by 1986 were traced throughout the period to estimate the fraction of land remaining continuously in the secondary vegetation category, possibly forming older secondary vegetation.

Alves, D.S., Soares, J.V., Amaral, S., Mello, E.M.K., Almeida, S.A.S., Silva, O.F., Silveira, A., 1997

Biomass of primary and secondary vegetation in RondŸnia, Western Brazilian Amazon

Global Change Biology (1997) 3, 451-461

Abstract: Biomass estimates of primary and different ages of secondary vegetation are reported for a tropical forest region in RondŸnia, Western Brazilian Amazon. The estimates are based on published allometric equations, and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18, years. Primary forest biomass estimates varied from 290 to 495 tha^-1. Secondary vegetation biomass estimates accounted for 40-60% of the primary forest biomass after 18 years of abandonment. Secondary growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 tha^-1yr^-1 between the third and the eighteenth years after abandonment. C0₂ sequestration by regrowing vegetation is discussed for two scenarios of land abandonment.

Alves D.S., da Costa W.M., Escada M.I.S., Lopes E.S.S., de Souza R.C.M., Ortiz J.D., 1998a

Anßlise da distribui‡ƒo espacial das taxas de desflorestamento dos munic�pios da AmazŸnia Legal no per�odo 1991-1994.Relatrio t‰cnico AMZ-R04/98. Sƒo Jos‰ dos Campos: Instituto Nacional de Pesquisas Espaciais, Maio 1998.

RESUMO: Uma anßlise da distribui‡ƒo espacial das taxas de desflorestamento na AmazŸnia Legal nos per�odos 1991-1992 e 1992-1994 ‰ apresentada para os munic�pios da regiƒo. O trabalho baseou-se nos mapas de ßreas desflorestadas elaborados pelo INPE a partir de imagens do sat‰lite Landsat 5 e no mapa de munic�pios do IBGE para o ano de 1994. A ßrea de estudo compreendeu as forma‡es florestais da AmazŸnia Legal, exclu�das as ßreas de cerrado e outras forma‡es nƒo florestais. Os resultados mais importantes incluem a determina‡ƒo dos munic�pios onde ocorreram as maiores taxas e uma anßlise das varia‡es das taxas entre os per�odos. Os munic�pios que apresentaram as maiores taxas de desflorestamento pertenceram aos flancos sul e leste da regiƒo e tamb‰m € por‡ƒo ocidental do Parß e a Roraima. Fra‡es importantes das maiores taxas foram verificadas em regies prximas a algumas das principais estradas da AmazŸnia.

Alves, D.S., Pereira, J.L.G., Souza, C.L., Soares, J.V., Yamaguchi, F., in press.

Characterizing landscape changes in Central RondŸnia using TM imagery. International Journal of Remote Sensing, 14, 2877-2882 (1999)

Abstract: An analysis of landscape changes in a region of pioneer settlements in central RondŸnia, western Brazilian Amazon, was developed for the period between 1977 and 1995. Total deforested area and the fraction of cleared forest (percent cleared) were derived from Landsat data and evaluated as a function of distance to areas of pioneer settlement and major roads in the region. Total deforested area changed from 206x103 hectares in 1977, to 565x103 hectares in 1985 and to 1,210x103 hectares, or 35.5 % of the region, in 1995. By 1995, 81% percent of the total deforestation had occurred in regions within 12.5 km from the areas deforested by 1977; percent cleared exceeded 79% in areas within 12.5 km from the region's first road.

Alves, D.S., 1999 (in press)

An analysis of the geographical patterns of deforestation in Brazilian Amazonia in the 1991-1996 period.

In: Land Use and Deforestation in the Amazon. Edited by Charles H. Wood and Roberto Porro

Abstract: Deforestation maps produced by INPE for the 1991-1996 period were stratified by 1/4^o grid cells and regions of more important deforestation were detected. Deforestation tended to be concentrated in a number of regions: 4% of the total number of cells accumulated 25% of the total observed deforestation and 10% of the cells accumulated 50% of the total deforestation. Ninety-five percent of the total deforestation was observed in 40% of the cells. Deforestation appeared to grow inertially around areas of pioneer deforestation (i.e. areas already deforested by 1978) and major roads: 86% of the observed deforestation was found within 25 km from areas already deforested by 1978; approximately 17% of the observed deforestation occurred within 50km from the western road network including the Cuiabß-Porto Velho-Rio Branco road link; 33% within 50km from the eastern road network, linking central Brazil to Parß and Maranhƒo; 24% within 50km from the central road network including the Cuiabß-Santar‰m and Transamazon highways and roads to northern-central Mato Grosso. Results show that most deforestation during the last three decades was circumscribed to relatively limited regions, potentially increasing environmental and social impacts in such areas.

Becker, B.K., 1997

AmazŸnia, Sƒo Paulo, Editora Âtica

Becker, B.K., 1996

Significado geopol�tico da AmazŸnia. Elementos para uma estrat‰gia. In: Uma estrat‰gia latino-americana para a AmazŸnia, V 3, organizador Crodowaldo Pavan, coordena‡ƒo editorial Maria Carolina de Araujo. Sƒo Paulo, Funda‡ƒo Memorial da Am‰rica Latina. 187-203

Boyd, D.S., Foody, G.M., Curran, P.J., Lucas, R.M., Honzak, M., 1996

An assessment of radiance in Landsat TM middle and thermal infrared wavebands for the detection of tropical forest regeneration

Int. J. Remote Sensing, 1996, 17, 249-261

Abstract. It has been postulated that tropical forests regenerating after deforestation constitute an unmeasured terrestrial sink of atmospheric carbon, and that the strength of this sink is a function of regeneration stage. Such regeneration stages can be characterized by biophysical properties, such as leaf and wood biomass, which influence the radiance emitted and/or reflected from the forest canopy. Remotely sensed data can therefore be used to estimate these biophysical properties and thereby determine the forest regenerative stage. Studies conducted on temperate forests have related biophysical properties successfully with red and near-infrared radiance, particularly within the Normalized Difference Vegetation Index (NDVI). However, only weak correlations have generally been observed for tropical forests and it is suggested here that the relationship between forest biophysical properties and middle and thermal infrared radiance may be stronger than that between those properties and visible and near-infrared radiance.

An assessment of Landsat Thematic Mapper (TM) data revealed that radiance acquired in middle and thermal infrared wavebands contained significant information for the detection of regeneration stages in Amazonian tropical forests. It was demonstrated that tropical forest regeneration stages were most separable using middle infrared and thermal infrared wavebands and that the correlation with regeneration stage was stronger with middle infrared, thermal infrared or combinations of these wavebands than they were with visible, near infrared or combinations of these wavebands. For example, correlation coefficients increased from û0.26 (insignificant at 95 per cent confidence level) when using the NDVI, to up to 0.93 (significant at 99 per cent confidence level) for a vegetation index containing data acquired in the middle and thermal infrared wavebands. These results point to the value of using data acquired in middle and thermal infrared wavebands for the study of tropical forests.

Brown, S., Lugo, A.E. Lugo, 1990

Tropical secondary forests

Journal of Tropical Ecology, 6, 1-32

ABSTRACT

The literature on tropical secondary forests, defined as those resulting from human disturbance (e.g. logged forests and forest fallows), is reviewed to address questions related to their extent, rates of formation, ecological characteristics, values and uses to humans, and potential for management. Secondary forests are extensive in the tropics, accounting for about 40% of the total forest area and their rates of formation are about 9 million hayr^-1. Geographical differences in the extent, rates of formation and types of forest being converted exist.

Secondary forests appear to accumulate woody plant species at a relatively rapid rate but the mechanisms involved are complex and no clear pattern emerged. Compared to mature forests, the structure of secondary forest vegetation is simple, although age, climate and soil type are modifying factors. Biomass accumulates rapidly in secondary forests, up to 100 t ha^-1 during the first 15 yr or so, but history of disturbance may modify this trend. Like biomass, high rates of litter production are established relatively quickly, up to 12-13 t ha^-1 yr^-1 by age 12-15 yr. And, in younger secondary forests (< 20 yr), litter production is a higher fraction of the net primary productivity than stemwood biomass production. More organic matter is produced and transferred to the soil in younger secondary forests than is stored in above-ground vegetation. The impact of this on soil organic matter is significant and explains why the recovery of organic matter in the soil under secondary forests is relatively fast (50 yr or so). Nutrients are accumulated rapidly in secondary vegetation, and are returned quickly by litterfall and decomposition for uptake by roots.

We propose a model of the gains and losses, yields and costs, and benefits and tradeoffs to people from the current land-use changes occurring in the tropics. When the conversion of forest lands to secondary forests and agriculture is too fast or land-use stages are skipped, society loses goods and services. To avoid such a loss, we advocate management of tropical forest lands within a landscape perspective, a possibility in the tropics because land tenures and development projects are often large.

Buschbacher, R., Uhl, C., Serrƒo, E.A.S., 1988

Abandoned pastures in eastern Amazonia. II. Nutrient stocks in the soil and vegetation

Journal of Ecology, 76, 682-699

SUMMARY

1. Soil nutrient content was studied in relation to vegetation development on thirteen abandoned pastures differing in age from two to eight years and in intensity of pasture use from light to heavy. The surface soils of these sites had higher cation concentration and pH than those of undisturbed mature forest of the area, but similar phosphorus, organic matter and total nitrogen concentrations.

2. Soil nutrient concentration generally was independent of age or prior intensity of use in the pastures. Pasture use has a significant effect on soil nutrient concentration when the sites are first abandoned, but this does not persist. Nutrient uptake by successional vegetation may substantially reduce soil nutrient stocks.

3. Soil nutrient concentration was not significantly correlated with vegetation biomass, primary tree biomass or species richness, either among or within sites.

4. Nutrient depletion of pastures abandoned eight years previously relative to total nutrient stocks in mature forest depended on pasture disturbance. Sites previously subjected to low use were only depleted of N, moderate-use sites were depleted of N and K, and heavy-use sites were depleted of N, K, Mg and possibly Ca and P. There was less nutrient depletion than the relatively small biomass of the successional sites would indicate. This was due to a higher proportion of nutrient-rich leaves and fine branches, enriched soil nutrient stocks relative to mature forest and, on the lightly disturbed sites, a large pool of nutrients in unburned woody residue.

5. Decomposition of unburned woody residue may provide one-half of the nutrients taken up by vegetation during eight years of recovery following light pasture use, but only 15% following moderate use, and none following the most intense use.

6. General schemes of succession following deforestation for pasture development are presented. Recovery after disturbance is complex, and follows different patterns depending on the intensity of pasture use.

Fearnside, P.M., Guimarƒes,W.M., 1996

Carbon uptake by secondary forests in Brazilian Amazonia

Forest Ecology and Management 80 (1996) 1-20

Abstract

Estimating the contribution of deforestation to greenhouse gas emissions requires calculations of the uptake of carbon by the vegetation that replaces the forest as well as the emissions from burning and decay of forest biomass and from altered emissions and uptakes by the soil. The role of regeneration in offsetting emissions from deforestation in the Brazilian Legal Amazon has sometimes been exaggerated. Unlike many other tropical areas, cattle pasture (rather than shifting cultivation) usually replaces forest in Brazilian Amazonia. Degraded cattle pastures regenerate secondary forests more slowly than do fallows in shifting cultivation systems, leading to lower uptake of carbon. The calculations presented here indicate that in 1990 the 410x10³ km² deforested landscape was taking up 29 x 10⁶ t of carbon (C) annually (0.7 t C ha^-1 year^-1). This does not include the emissions from clearing of secondary forests, which in 1990 released an estimated 27x10⁶ t C, almost completely offsetting the uptake from the landscape. Were the present land-use change processes to continue, carbon uptake would rise to 365 x10⁶ t annually (0.9 t C ha^-1 year^-1) in 2090 in the 3.9x10⁶ km2 area that would have been deforested by that year. The 1990 rate of emissions from deforestation in the region greatly exceeded the uptake from regrowth of replacement vegetation.

Fearnside, P.M., 1996b

Amazonian deforestation and global warming: carbon stocks in vegetation replacing BrazilÆs Amazon forest

Forest Ecology and Management 80 (1996) 21-34

Abstract

Carbon stocks in vegetation replacing forest in Brazilian Amazonia affect net emissions of greenhouse gases from land-use change. A Markov matrix of annual transition probabilities was constructed to estimate landscape composition in 1990 and to project future changes, assuming behavior of farmers and ranchers remains unchanged. The estimated 1990 landscape was 5.4% farmland, 44.8% productive pasture, 2.2% degraded pasture, 2.1% 'young' (1970 or later) secondary forest derived from agriculture, 28.1 % 'young' secondary forest derived from pasture, and 17.4% 'old' (pre-1 970) secondary forest. The landscape would eventually approach an equilibrium of 4.0% farmland, 43.8% productive pasture, 5.2% degraded pasture, 2.0% secondary forest derived from agriculture, and 44.9% secondary forest derived from pasture. An insignificant amount is regenerated 'forest' (defined as secondary forest over 100 years old). Average total biomass (dry matter, including below-ground and dead components) was 43.5 t ha^-1 in 1990 in the 410 x 10³ km² deforested by that year for uses other than hydroelectric dams. At equilibrium, average biomass would be 28.5 t ha^-1 over all deforested areas (excluding dams). These biomass values are more than double those forming the basis of deforestation emission estimates currently used by the Intergovernmental Panel on Climate Change (IPCC). Although higher replacement landscape biomass decreases net emissions from deforestation, these estimates still imply large net releases.

Fearnside, P.M., 1997

Limiting factors for development of agriculture and ranching in Brazilian Amazonia

Rev. Brasil. Biol., 1997, 57, 531-549

ABSTRACT

Limiting factors restrict both the intensification of agriculture and ranching uses and the scale to which these land uses can be expanded. The expression of limiting factors on development is mediated through human planning: the perception of limits to agricultural yields and of the severity and probability of environmental impacts can lead to decisions to limit agricultural expansion. Limits to intensification of agriculture include agronomic limits on per-hectare yields, technological limits and research, and cultural limits. Limits to expansion of agricultural areas include physical resource limits such as phosphate deposits, limits of social values, institutional limits (including the credibility of institutions), limits on human habitation (such as health), and limits to environmental risks. Limits from considerations in political and military spheres often override "rational" decisions based on land capability and environmental consequences. This kind of "interference", however, can cause a variety of impacts that, if properly evaluated, would likely make the net result of such development projects a negative one for Brazil's national interests.

Fran‡ois, L.M., Delire, C., Warmant, P., Munhoven, G., 1998

Modelling the glacial-interglacial changes in the continental biosphere

Global and Planetary Change 6-177(1998)37-52

Abstract

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to drive the biosphere model are derived from results of the ECHAM2 General Circulation Model (GCM). Six model simulations (four under typical interglacial and two under typical glacial climatic conditions) were performed to analyse the roles of different environmental changes influencing the biospheric net primary productivity (NPP) and carbon stocks. The main differences between these simulations come from the adopted CO, levels in the atmosphere, the presence or absence of crops and from changing continental boundaries. The variation of the terrestrial carbon stocks since the LGM are estimated by comparing the pre-agricultural (280 ppm of CO₂, no crops, modern climate) and the full glacial simulations (200 ppm of CO₂, LGM climate reconstruction). Our model predicts a global NPP increase from 38 Gt C year^-1 to 53 Gt C year^-1 during the deglaciation, a substantial part of that change being due to CO₂ fertilization. At the same time, the terrestrial biosphere would have fixed between 134 (neglecting CO, fertilization effects) and 606 Gt C. The treatment of both the C₃ and C₄ photosynthetic pathways in the CARAIB model enabled us further to reconstruct the partitioning between C₄ and C₃ plants. Following our experiments, 29.7% of the total biospheric carbon stock at the LGM was C₄ material, compared to an interglacial fraction of only 19.8%. The average biospheric fractionation factor was ~1.5% less negative at LGM than it is today. Considering an atmospheric d¹³C 0.5 ˜ 0.2% lower at LGM than at pre-industrial times, the 606 Gt C transfer would lead to a global ocean d¹³C shift of roughly -0.41%c, fully consistent with currently available data. For the smaller change of 134 Gt C obtained without the CO₂ fertilization effect, this shift would only be on the order of -0.10%.

Frohn, R.C, McGwire, K.C., Dale, V.H., Estes, J.E, 1996

Using satellite remote sensing analysis to evaluate a socioeconomic and ecological model of deforestation in RondŸnia, Brazil

INT. J. REMOTE SENSING, 1996, 17, 3233-3255

Abstract

The effectiveness of an integrated socioeconomic and ecological simulation model for estimating patterns and rates of deforestation in RondŸnia, Brazil is evaluated using Landsat data and landscape pattern metrics. The Percent Cleared, Contagion, and Fractal Dimension of image classifications are compared to those determined from model outputs. Results indicate that rates and spatial patterns of deforestation are similar between model outputs and Landsat image analysis. Differences in clearing patterns between the model and Landsat data are due in part to topography, localized farming obstacles and the patchiness of clearings. The effects of varying spatial resolution on the metrics is also examined.

Grace, J., Lloyd, J., McIntyre, J., Miranda, A.C., Meir, P., Miranda, H.S., Nobre, C., Moncrieff, J., Massheder, J., Malhi, Y., Wright, I., Gash, J., 1995

Carbon Dioxide Uptake by an Undisturbed Tropical Rain Forest in Southwest Amazonia, 1992 to 1993

Science, 270, 778-780

Measurements of carbon dioxide flux over undisturbed tropical rain forest in Brazil for 55 days in the wet and dry seasons of 1992 to 1993 show that this ecosystem is a net absorber of carbon dioxide. Photosynthetic gains of carbon dioxide exceeded respiratory losses irrespective of the season. These gains cannot be attributed to measurement error, nor to loss of carbon dioxide by drainage of cold air at night. A process-based model, fitted to the data, enabled estimation of the carbon absorbed by the ecosystem over the year as 8.5 ˜ 2.0 moles per square meter per year.

Green, G.M., Sussman, R.W.,1990

Deforestation History of the Eastern Rain Forests of Madagascar from Satellite Images

Science, 248, 212-215

Abstract

Madagascar is biologically one of the richest areas on Earth, and its plants and animals are among the most endangered. Satellite images and vegetation maps based on earlier aerial photographs were used to determine the extent of eastern rain forests in Madagascar and to monitor the rate of deforestation over a 35-year period. In 1985, 3.8 million hectares of rain forest remained, representing only 50 percent of the 7.6 million hectares existing in 1950 and 34 percent of the estimated original extent (I 1.2 million hectares). Between 1950 and 1985, the rate of deforestation averaged 111,000 hectares per year. Deforestation was most rapid in areas with low topographic relief and high population density. If cutting of forest continues at the same pace, only forests on the steepest slopes will survive the next 35 years.

Hardin, G

The Tragedy of the Commons

Science, 162, 1243-1248

Houghton, R.A., Lefkowitz, D.S. and Skole, D.L., 1991a

Changes in the landscape of Latin America between 1850 and 1985 I. Progressive loss of forests.

Forest Ecology and Management, 38 (1991) 143-172

Abstract

Reduction in the area of forests in Latin America between 1850 and 1985 was estimated from changes in the major uses of land, including permanent croplands, pastures, shifting cultivation, logging, and degradation. Changes in croplands were documented through historical statistics. The types of forests and other natural ecosystems converted to croplands were estimated from a comparison of maps of natural vegetation with maps of agriculture. Changes in the area of pastures were inferred from changes in the number of cattle and stocking rates. Estimates of the rate of deforestation for shifting cultivation were available only in recent years. Before 1940 the area in shifting cultivation was assumed constant; between 1940 and 1985 the increase in area was assumed to accelerate. In recent decades, the area of forests has decreased more rapidly than increases in the areas of croplands and pastures. This additional loss of forests is thought to have resulted from the replacement of degraded agricultural land, and was estimated to have occurred historically according to different assumptions. The results showed that, between 1850 and 1985, about 370 X 10' ha of forest (28% of the forest area in 1850) were replaced by some other type of ecosystem. Most of this reduction of forest area was due to the expansion of pastures (44% of the reduction), croplands (25%), degraded lands (20%), and shifting cultivation (10%). The use of alternative data and assumptions gave estimates of total deforestation that ranged between 313 and 412x10⁶ ha (25-30% of the area in 1850). The largest uncertainties were related to historical rates of degradation and shifting cultivation, and to the types of ecosystems converted to human uses. Use of satellite imagery can eliminate most of these uncertainties after 1975.

Houghton, R.A., Skole, D.L. and Lefkowitz, D.S., 1991b

Changes in the landscape of Latin America between 1850 and 1985: II. Net release of C02 to the atmosphere.

Forest Ecology and Management, 38 173-199.

Abstract

The net release of carbon to the atmosphere from deforestation in Latin America was calculated for the period 1850-1985. Changes in the area of forests were described in a companion paper. Here, the stocks of carbon in vegetation and soils of major ecosystems, and changes in these stocks of carbon as a result of disturbance, were used to calculate the net annual flux of carbon. The total net release of carbon between 1850 and 1985 was about 30x10¹⁵ g (range 17-35 x 10¹⁵ g). The land uses responsible for the emissions of carbon were increased areas of pastures (42% of the total emissions), croplands (34%), degraded lands (19%), and shifting cultivation (5%). Logging and the establishment of plantations contributed or accumulated negligible amounts of C over this 135-year period. The annual releases of C to the atmosphere increased over the period 1850-1985; half of the total release occurred after 1960. By 1985 the net release was 0.67 x 10" g C year^-' (range 0.39-0.82 x 10¹⁵ g C). The relative contributions of different land uses to this flux were different from those over the long-term. The greatest single source of C in 1985 resulted from increases in the area of degraded lands (37% of the net flux), and the importance of shifting cultivation increased to almost 20%. The range of estimates calculated here for the current net flux of C is lower than earlier estimates of the range. The range results from uncertainties in the rates of land-use change, in the types of ecosystems cleared and the stocks of C in these ecosystems, and in the rates of decay and regrowth of organic matter associated with land-use change.

Houghton, R. A. 1991

Releases of carbon to the atmosphere from degradation of forests in tropical Asia.

Can. J. For. Res. 21: 132-142.

Abstract

The net annual flux of carbon from south and southeast Asia as a result of changes in the area of forests was calculated for the period 1850 to 1985. The total net flux ranged from 14.4 to 24.0 Pg of carbon, depending on the estimates of biomass used in the calculations. High estimates of biomass, based on direct measurement of a few stands, and low estimates of biomass, based on volumes of merchantable wood surveyed over large areas, differ by a factor of almost 2. These and previous estimates of the release of carbon from terrestrial ecosystems to the atmosphere have been based on changes in the area of forests, or rates of deforestation. Recent studies have shown, however, that the loss of carbon from forests in tropical Asia is greater than would be expected on the basis of deforestation alone. This loss of carbon from within forests (degradation) also releases carbon to the atmosphere when the products removed from the forest burn or decay. Thus, degradation should be included in analyses of the net flux of carbon from terrestrial ecosystems. Degradation may also explain some of the difference between estimates of tropical forest biomass if the higher estimates are based on undisturbed forests and the lower estimates are more representative of the region. The implication of degradation for estimates of the release of carbon from terrestrial ecosystems is explored. When degradation was included in the analyses, the net flux of carbon -between 1850 and 1985 was 30.2 Pg of carbon, about 25% above that calculated on the basis of deforestation alone (with high estimates of biomass), and about I 10% above that calculated with low estimates of biomass. Thus, lower estimates of biomass for contemporary tropical forests do not necessarily result in lower estimates of flux.

Houghton, R.A., 1993

IS CARBON ACCUMULATING IN THE NORTHERN TEMPERATE ZONE ?

GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 7, NO. 3, PAGES 611-617, SEPTEMBER 1993

Abstract.

The current imbalance in the global carbon budget ('missing carbon') is approximately 1.5 to 2-0 PgC/yr. The study by Tans et al. [1990], based on geographically based estimates of industrial emissions, atmospheric data, and a model of atmospheric transport, suggested the missing carbon was accumulating in terrestrial ecosystems of the northern hemisphere's temperate zone. Two recent analyses of forest growth in this region have reported an accumulation of carbon that approaches, 1 PgC/yr, and on the basis of these three studies one might conclude that the carbon budget is close to balanced. These recent analyses are incomplete, however. They included the accumulation of carbon in regrowing forests logged during the last several decades but not the emissions of carbon from plant material initially held in those forests before logging. When all of the carbon is accounted for, the net flux of carbon (to forests as well as from forest products and logging debris) is close to zero in these regions. Thus the recent analyses have not uncovered a missing sink for carbon, as claimed. On the contrary, they seem to have confirmed that the current imbalance in the carbon budget cannot be explained by the net accumulation of wood in northern forests. If the entire global imbalance is accumulating in the biomass of these forests, the required accumulation rate is too large to have been missed by forest surveys. An annual flux of 1.5 to 2.0 PgC/yr seems too large to be accommodated in aboveground vegetation anywhere.

Houghton, R.A., 1998

Forest Resources: Past, Present and Future Role of Managed and Unmanaged Forests in the Global Carbon Balance, 1.1 Historic role of forests in the Global Carbon Cycle.

In: Carbon Dioxide Mitigation in Forestry and Wood Industry, edts. G.H. Kohlmaier, M. Weber, R.A. Houghton, Springer Verlag Berlin, 1998

ABSTRACT

The amount of carbon held in the world's forests has varied over time as a result of changes in both climate and human Activity. Climatic changes associated with the advance and retreat of glaciers may have reduced and enhanced terrestrial carbon storage by 300-1000 PgC ever a few thousand years. Growth of settled agriculture over the last 10,000 years may have reduced terrestrial carbon storage by 250-350 PgC. Neither change is well known, either in magnitude or rate. Before 1850 the long-term reductions in carbon storage attributable to humans probably had a small effect on atmospheric C0₂ because ancient civilizations grew and declined asynchronously, and thus the rate at which carbon was released to the atmosphere from conversion of forests to agricultural lands was slow relative to the rate at which the oceans could absorb C0₂.

From 1850 to the present, however, human clearing and harvesting of forests has contributed about a third of the increased concentrations of C0₂ observed in the atmosphere. Over the period 1850 to 1990 about 100 PgC are estimated to have been transferred from forests to the atmosphere as a result of human activity, two thirds from tropical forests and one third from temperate zone and boreal forests. Another 15 PgC were lost from non-forests, largely as a result of cultivation of mid-latitude grassland soils. During the same 140-year period about 800 x 10⁶ ha of forests were cleared for pastures and croplands, and approximately 1200x10⁶ ha were harvested. Conversion of forests to agricultural lands released about 75 PgC; harvest of wood released about 25 PgC. These estimates of release include the accumulations of carbon in wood products (19 PgC) and woody debris (9 PgC), the losses of carbon from oxidation of wood products, woody debris, and soil organic matter (400 PgC), and the accumulations of carbon in forests recovering from harvest (300 PgC). Over the same interval in which 100 PgC were lost from forests as a result of agricultural expansion and harvests, other factors appear to have caused an accumulation of carbon on land (as much as 75 PgC, according to geochemical analyses). Neither the locations nor the mechanisms of this accumulation are known. Possible mechanisms include environmental change as well as changes in silvicultural or other management techniques, including fire suppression. In the decade of the 1980s, forest inventories show an accumulation of about 0.6 PgC yr^-1 in northern mid-latitude forests. This accumulation is greater than expected from recovery of forests from earlier harvests and suggests that these forests account for a small fraction of the 2.0-3.5 PgC yt^-1 accumulation calculated by geochemical analyses.

Houghton, R.A., Skole, D.L., Nobre, C.A., Hackler, J.L., Lawrence, K.T., Chomentowski, W.H. 2000

Annual fluxes of carbon from deforestation and regrowth in the Brazilian Amazon

Nature, 403, 301-304

Abstract

The distribution of sources and sinks of carbon among the worldÆs ecosystems in uncertain. Some analyses show northern mid-latitude lands to be a large sink, whereas the tropics are a net source; other analyses show the tropics to be nearly neutral whereas northern mid-latitudes are a small sink. Here we show that the annual flux of carbon from deforestation and abandonment of agricultural lands in the Brazilian Amazon was a source of about 0.2 Pg C/yr over the period 1989-1998. This estimate is based on annual rates of deforestation and spatially detailed estimates of deforestation, regrowing forests and biomass. Logging may add another 5-10% to this estimate, and fires may double the magnitude of the source in years following a drought. The annual source of carbon from land-use change and fire approximately offsets the sink calculated for natural ecosystems in the region. Thus this large area of tropical forest is nearly balanced with respect to carbon, but has an interannual variability of +/- 0.2 PgC/yr.

Idso, S.B., Kimball, B.A., 1993

TREE GROWTH IN CARBON DIOXIDE ENRICHED AIR AND ITS IMPLICATIONS FOR GLOBAL CARBON CYCLING AND MAXIMUM LEVELS OF ATMOSPHERIC CO₂

Global Biogeochemical Cycles, 7, 537-555

Abstract

In the longest carbon dioxide enrichment experiment ever conducted, well-watered and adequately fertilized sour orange tree seedlings were planted directly into the ground at Phoenix, Arizona, in July 1987 and continuously exposed, from mid-November of that year, to either ambient air or air enriched with an extra 300 ppmv of C02 in clear-plastic-wall open-top enclosures. Only 18 months later, the C02-enriched trees had grown 2.8 times larger than the ambient-treated trees; and they have maintained that productivity differential to the present day. This tremendous growth advantage is due to two major factors: a C02-induced increase in daytime net photosynthesis and a C02-induced reduction in nighttime dark respiration. Measurements of these physiological processes in another experiment have shown three Australlian tree species to respond similarly; while an independent study of the atmosphere's seasonal CO₂ cycle suggests that all earth's trees, in the mean, probably share this same response. A brief review of the plant science literature outlines how such a large growth response to atmospheric C02 enrichment might possibly be maintained in light of resource limitations existing in nature. Finally, it is noted that a C02 'fertilization effect" of this magnitude should substantially slow the rate at which anthropogenic carbon dioxide would otherwise accumulate in the atmosphere.

Instituto Nacional de Pesquisas Espaciais (INPE), 1998.

INPE atualiza os dados do desflorestamento na AmazŸnia, de 95 a 97. INPE Not�cias.N^o 13, jan.-feb. 1998, 1-2.

Kramer, P.J., Sionit, N., 1987

Efects of increasing carbon dioxide concentration on the physiology and growth of forest trees

In: The Greenhouse Effect, Climate Change and U.S. Forests. Edts. Shards, W.E. and J.S. Hoffman, The Conservation Foundation, Washington D.C., 1987

ABSTRACT

Short-term experiments indicate that increasing the concentration of atmospheric carbon dioxide (CO₂) increases stem diameter, height, and dry weight of seedlings of several tree species. A high CO₂ concentration also increases branching, leaf area, and leaf thickness in some but not all species. Root-shoot ratio does not seem to be significantly affected. At the end of the first growing season, dry weights of roots, stems, and leaves of sweetgum and loblolly pine seedlings were greater at 500 than at 360 parts per million (ppm) of CO₂. Sweetgum also produced more branches and leaves at the higher concentration. There was no significant increase in dry weight of roots, stems, or leaves at 660 ppm over the value of 500 ppm, but there was a significant increase in height of loblolly pine seedlings. It seems probable that if other environmental factors are not severely limiting, the increasing concentration of atmospheric CO₂ will significantly increase tree growth, but the magnitude of the effects will vary among species and with the severity of other environmental stresses. Although increasing concentration of C0₂ may partly compensate for low light, high temperature, and water stress and possibly even for mineral deficiencies, unfavorable factors such as droughts, abnormal temperatures, and unfavorable soil conditions will continue to limit tree growth. There is need for more long-term research to provide reliable information concerning the effects of CO₂ buildup on the relative growth of commercially important species.

Lee, K., Wanninkhof, R., Takahashi, T., Donoy, S.C., Feely, R.A., 1998

Low interannual variability in recent oceanic uptake of atmospheric carbon dioxide

Nature, 396, 155-159

An improved understanding of the partitioning of carbon between the atmosphere, terrestrial biosphere, and ocean allows for more accurate predictions of future atmospheric C0₂ concentrations under various fossil-fuel C0₂-emission scenarios. One of the more poorly quantified relevant processes is the interannual variability in the uptake of fossil-fuel C0₂ from the atmosphere by the terrestrial biosphere and ocean. Existing estimates, based on atmospheric measurements, indicate that the oceanic variability is large. Here we estimate the interannual variability in global net air-sea CO₂ flux using changes in the observed wind speeds and the partial pressure of CO₂ (pCO₂) in surface sea water and the overlying air. Changes in seawater pCO₂ are deduced from interannual anomalies in sea surface temperature and the regionally and seasonally varying temperature-dependence of seawater pCO₂, assuming that variations in sea surface temperature reflect seawater pCO₂ changes caused by thermodynamics, biological processes and water mixing. The calculated interannual variability in oceanic CO₂ uptake of 0.4 GtCyr^-1 (2s) is much less than inferred from the analysis of atmospheric measurements. Our results suggest that variable sequestration of carbon by the terrestrial biosphere is the main cause of observed year-to-year variations in the rate of atmospheric CO₂ accumulation.

Lisboa, P.L.B., 1989

Estudo flor�stico da vegeta‡ƒo arbrea de uma floresta secundßria, em RondŸnia.

Boletim Museu Paraense Em�lio Goeldi, s‰rie Bot‚nica, 5, 145-162

ABSTRACT - A botanical survey was made of a 0.5 hectare plot of secondary forest located along the BR-364 highway (Cuiabß- Porto Velho), at km 17, between Jiparanß and Presidente Medici, in the Brazilian state of RondŸnia. The study area was divided into 20 plots of 25x10m. In total, 113 plant species, belonging to 39 families, were found, including 760 tree species with DBH > 15 cm. Total basal area was 11.741 m². The most important plant families (F.I.V.) were Cochlospermacceae, Leguminosae, Moraceae, Euphorbiaceae and Caricaceae. The most important species were Cochlospermum orinoccense, Sapium marmieri, Inga edulis, Apeiba albillora and Cecropia sciadophila.

Comparisons were made between primary and secondary florests in terms of floristic composition and vegetational structure, and the results showed a marked alteration of flora and biomass after the removal of the primary forest cover. An evaluation of the economic potential of forest species is also presented.

Lugo, A.E., Brown, S., 1992

Tropical forests as sinks of atmospheric carbon

Forest Ecology and Management, 54 (1992)

ABSTRACT

Changes in land use and rates of carbon accumulation by land use including mature, logged, and fallow tropical forests, and degraded tropical lands are used to estimate the role that the tropical landscape serves as sinks of atmospheric carbon. Results indicate that in 1980 tropical lands may remove between 1.5 and 3.2 Pg C from the atmosphere. We excluded from the analysis some 900 million ha of open tropical forests that could also be removing carbon from the atmosphere and an additional 0.5-0.6 Pg C yr-1 sink associated with carbon export by rivers and in wood products. Our analysis challenges assumptions about the steady-state condition of the carbon budget of mature tropical forests and suggests that large areas of the tropical landscape are recovering from disturbance and act as atmospheric carbon sinks. We focus attention on sinks of atmospheric carbon only. In 1980, the estimated accumulation of carbon in the recovering landscape was equal to the net carbon flux due to tropical deforestation.

Machado, L, 1998

A fronteira agr�cola na AmazŸnia

In: Geografia e Meio Ambiente, Edts. B.K. Becker, A. Christofoletti, F.R. Davidovich, P.P. Geiger (Sƒo Paulo: Hucitec), 181-217

Melillo, J.M., McGuire, A.D., Kicklighter, D.W., Moore III, B., Vorosmarty, C.J., Schloss, A.L., 1993

Global climate change and terrestrial net primary production

Nature, 363, 234-240

A process-based model was used to estimate global patterns of net primary production and soil nitrogen cycling for contemporary climate conditions and current atmospheric C0₂ concentration. Over half of the global annual net primary production was estimated to occur in the tropics, with most of the production attributable to tropical evergreen forest. The effects of C0₂ doubling and associated climate changes were also explored. The responses in tropical and dry temperate ecosystems were dominated by C0₂, but those in northern and moist temperate ecosystems reflected the effects of temperature on nitrogen availability.

Myneni, R.B., Keeling, C. D., Tucker, C.J., Asrar, D., Nemani, R. R. 1997

Increased plant growth in the northern high latitudes from 1981 to 1991

Nature, 386, 698-702

Variations in the amplitude and timing of the seasonal cycle of atmospheric C0₂ have shown an association with surface air temperature consistent with the hypothesis that warmer temperatures have promoted increases in plant growth during summer and/or plan respiration during winter in the northern high latitudes. Here we present evidence from satellite data that the photosynthetic activity of terrestrial vegetation increased from 1981 to 1991 in a manner that is suggestive of an increase in plant growth associated with a lengthening of the active growing season. The regions exhibiting the greatest increase lie between 45^oN and 70^oN, where marked warming has occurred in the spring time due to an early disappearance of snow. The satellite data are concordant with an increase in the amplitude of the seasonal cycle of atmospheric carbon dioxide exceeding 20% since the early 1970s, and an advance of up to seven days in the timing of the drawdown of C0₂ in spring and early summer. Thus, both the satellite data and the C0₂ record indicate that the global carbon cycle has responded to interannual fluctuations in surface air temperature which, although small at the global scale, are regionally highly significant.

Phillips, O.L., Malhi, Y., Higuchi, N., Laurance, W.F., Nu±ez, P.V., Vßsquez, R.M., Laurance, S.G., Ferreira, L.V., Stern, M., Brown, S., Grace, J.

Changes in the Carbon Balance of Tropical Forests: Evidence from Long-Term Plots

Science, 282, 439-446

The role of the world's forests as a "sink" for atmospheric carbon dioxide is the subject of active debate. Long-term monitoring of plots in mature humid tropical forests concentrated in South America revealed that biomass gain by tree growth exceeded losses from tree death in 38 of 50 Neotropical sites. These forest plots have accumulated 0.71 ton, plus or minus 0.34 ton, of carbon per hectare per year in recent decades. The data suggest that Neotropical forests may be a significant carbon sink, reducing the rate of increase in atmospheric carbon dioxide.

Santos, M., 1996

Por uma Geografia Nova. Da cr�tica da Geografia a uma Geografia Cr�tica. Sƒo Paulo, Hucitec.

Tans, P.P., Fung, I.Y., Takahashi, T., 1990

Observational constraints on the global atmospheric CO₂ budget

Science, 1990, 247, 1431-1438

Abstract

Observed atmospheric concentrations of CO₂ and data on partial pressures of CO₂ in surface ocean waters are combined to identify globally significant sources and sinks of CO₂. The atmospheric data are compared with boundary layer concentrations calculated with the transport field generated by a general circulation model (GCM) for specified source-sink distributions. In the model the observed north-south atmospheric concentration gradient can be maintained only if sinks for CO₂ are greater in the Northern than in the Southern Hemisphere. The observed differences between the partial pressure of CO₂ in the atmosphere are too small for the oceans to be the major sink of fossil fuel CO₂. Therefore, a large amount of the CO₂ is apparently absorved on the continents by terrestrial ecosystems.

Tardin, A.T., Lee, D.C.L., Santos, R.J.R., Assis, O.R., Barbosa, M.P.S., Moreira, M.L., Pereira, M.T., Silva, D., Santos Filho, C.P. 1980.

Subprojeto desmatamento: convŠnio IBDF/CNPq - INPE. Relatrio INPE-1649-RPE/103. Sƒo Jos‰ dos Campos: Instituto de Pesquisas Espaciais, 1980.

Uhl, C., Buschbacher, R., Serrƒo, E.A.S.

Abandoned pastures in eastern Amazonia. I. Patterns of plant succession

Journal of Ecology, 76, 663-681

SUMMARY

1. Vegetation composition, structure, and biomass accumulation were studied on thirteen forest sites that had been cut and burned, used as cattle pasture, and then abandoned in the eastern Amazon near Paragominas, Parß, Brazil.

2. The study sites were of two ages (two to four years and seven to eight years) and had received light, medium or heavy use for up to thirteen years.

3. Forest regenerated vigorously on sites of previously light use. Aboveground biomass accumulation averaged 10 t ha^-1y^-1 or 80 t after eight years (roughly one-quarter of mature forest levels). Tree species richness was also high (about 20 per 100 m2) and almost all species occurred in native forest. Moderately grazed pastures also developed forest but accumulation was only 5 t ha^-1y^-1. Tree species richness was also lower than on light-use sites and there were fewer forest trees. Abandoned pastures subjected to heavy use had the least distinct patterns of succession. The single eight-year-old site was dominated by grasses and forbs with fewer than one tree per 100 m2 and an above-ground accumulation of 0.6 t ha^-1y^-1, a value only about 6% of that found on light-use sites.

4. The light-use sites had significantly higher biomass and species richness in both age-classes than either moderate- or heavy-use sites. Site age was a good predictor of above-ground biomass accumulation on light- and moderate use sites, but not on heavy-use sites.

5. These Amazon ecosystems generally can recover after large-scale pasture disturbances. Only where land has been used too intensively for long periods is reforestation uncertain, but probably less than 10% of the pasture land in northern Parß has degraded to this level. Nevertheless, the re-growth forest, regardless of pasture-use history, will not necessarily have the same characteristics of physiognomy or species composition as that originally occupying the site. Moreover, as burning becomes more prevalent in eastern Amazonia, abandoned sites may not develop into forest and the irreversible degradation of the entire regional ecosystem must be contemplated.

Victoria, R.L., Fernandes, F., Martinelli, L.A., Piccolo, M.C., Camargo, P.B., Trumbore, S., 1995

Past vegetation changes in the Brazilian Pantanal arboreal-grassy savanna ecotone by using carbon isotopes in the soil organic matter

Global Change Biology (1995) 1,165-171

Abstract

Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in ¹³C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM ¹³C values reflect the change from C₃ to C₄ plants between the sites, as confirmed by measurements of ¹³C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of ¹³C in SOM with depth at both sites are larger than the 3-4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C₃ and C₄ plants at these sites. Mass balances with ¹⁴C and ¹³C suggest that past vegetational changes from C₃ to C₄ plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C₄ to C₃, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime.

V÷r÷smarty, C.J., Moore II, B., Grace, A.L., Gildea, M.P., Melillo, J.M., Peterson, B.J., 1989

Continental scale models of water balance and fluvial transport: an application to South America.

Global Biogeochemical Cycles, 3, 241-265

Abstract

A coupled water balance and water transport model (WBM/WTM) was constructed as part of a larger study of global biogeochemistry. The WBM/WTM provides critical hydrological information to models of terrestrial primary production, organic matter decay, riverine nutrient flux and trace gas exchanges with the troposphere. Specifically, it creates high-resolution datasets for monthly soil moisture, evapotranspiration, runnoff, river discharge and floodplain inundation. As a first step towards eventual global coverage, the WM/WTM weas applied to South America, represented by more than 5700 1/2^o (latitude/longitude) grid cells. The WBM transforms spatially complex data on long-term climate, vegetation, soils and topography into predictions of soil moisture (SM), evapotranspiration (ET) and runnof (RO). For South America, field capacity (FC) ranged from 27 to 582 mm of water, and computed values for mean annual SM, ET and RO were 284 mm, 1059 mm/yr and 619 mm/yr, respectively. There were large differences regionally and over the year. The transport model uses WBM-derived runoff, information on fluvial topology, linear transfer through river channels and a simple representation of floodplain inundation to generate monthly discharge estimates for any cell within a simulated catchment. The WTM succesfully determined the timing and magnitude of discharge at selected locations within the Amazon/Tocantins basin. It also demonstrated the importance of floodplain inundation in defining flow regime on the mainstem Amazon. Estimated mean annual discharge was 207,000 m³/s for the Amazon River and 17,000 m³/s for the Tocantins. In the basins, 45% of the incident precipitation emerges as river flow, 55% is lost to ET. The model described in this paper will be expanded to include the dynamics of carbon, major nutrients and sediments. It will serve as a semimechanistic tool to quantify the transport of materials from the landscape to the worldÆs oceans. Such a capability becomes increasingly important as we seek to understand the impacts of climate and land use change on major river system of the globe.

Walker, R.T., Homma, A.K.O., Scatena, F.N., Conto, A.J., Rodriquez-Pedrazza, C.D., Ferreira, C.A.P., Oliveira, P.M., Carvalho, R.A., 1997

Land cover evolution of small properties: the Transamazon Highway

Revista de Economia e Sociologia Rural, 35, 115-126, abr./jun. 1997.

ABSTRACT

The dynamics of land use change in both the mid and long-run were determined for a sample of 132 small farmers along the Transamazon Highway. On average, four deforestation events occurred after arrival on the property. The average amount of land deforested was 10 hectares for each event, totaling 40 of the 50 hectares allowed by law for a typical size plot of 100 hectares. It was observed that small farmers along the Transamazon Highway employ diversified systems of land use including annual crops, perennials and cattle; these show a temporal sequence in accord with household domestic cycles. These results suggest that pasture conversion in Amazon by small farmers is due to domestic cycle dynamics in addition to others variables.

Wofsy, S. C. , Goulden, M. L. , Munger, J. W., Fan, S.M., Bakwin, P. S. , Daube, B. C. , Bassow, S. L., Bazzaz, F. A., 1992

Net Exchange of C0₂ in a Mid-Latitude Forest

Science, 260, 1314-1317

Abstract

The eddy correlation method was used to measure the net ecosystem exchange of carbon dioxide continuously from April 1990 to December 1991 in a deciduous forest in central Massachusetts. The annual net uptake was 3.7 + 0.7 metric tons of carbon per hectare per year. Ecosystem respiration, calculated from the relation between nighttime exchange and soil temperature, was 7.4 metric tons of carbon per hectare per year, implying gross ecosystem production of 11.1 metric tons of carbon per hectare per year. The observed rate of accumulation of carbon reflects recovery from agricultural development in the 1800s. Carbon uptake rates were notably larger than those assumed for temperate forests in global carbon studies. Carbon storage in temperate forests can play an important role in determining future concentrations of atmospheric carbon dioxide.

Woodward, F.I., Thompson, G.B., McKee, I.F., 1991

The Effects of Elevated Concentrations of Carbon Dioxide on Individual Plants, Populations, Communities and Ecosystems

Annals of Botany, 67 (Supplement 1), 23-38, 1991

Abstract

Changes in the atmospheric concentration of CO₂, over periods of millennia, are positively correlated with the temperature of the world. It is expected that this positive correlation will be manifested in the future, warmer ægreenhouse worldÆ with higher concentrations of CO₂. The predicted changes in temperature and precipitation are expected to cause significant changes in the distribution patterns of the world's terrestrial vegetation (Woodward and McKee, 1991).

In addition to this indirect effect, CO₂ influences plants directly and an increase in the concentration of CO₂ may increase the rate of photosynthesis with the C₃ pathway of fixation. Experimental observations often differ in the degree and length of this stimulation, reflecting the stronger impact of other photosynthetic limitations. Where photosynthetic stimulation does occur there is a general decrease in leaf protein, which may stimulate rates of leaf herbivory. The well established and associated increase in the C/N ratio of individual leaves should reduce rates of leaf decomposition. However the few community experiments at elevated CO₂ suggest little change in the rate of nutrient cycling in communities.

Stomatal opening is generally reduced as CO₂ concentration increases. This feature scales up through to the community level, however, it appears that the total volume of water used by a community is unlikely to alter with CO₂ alone, because plants tend to develop leafier canopies. This change, plus enhanced rates of root development, indicate a greater potential for carbon sequestration by terrestrial ecosystems. Monthly observations of atmospheric CO₂ concentration above the tundra over the last 14 years indicate these expected increases in the rates of CO₂ drawdown by the northern ecosystems of the tundra and the boreal and temperate deciduous forests. However, some of this change may be due to interactions with the warmer climate of the 1980s and perhaps an increased aerial supply of pollutant nitrogen.