Calibration and testing or models of the global carbon cycle

A ten-compartment model of the global biogeochemical cycle of carbon is presented. The two less-abundant isotopes of carbon, /sup 13/C and /sup 14/C, as well as total carbon, are considered. The cycling of carbon in the ocean is represented by two well-mixed compartments and in the world's terrestrial ecosystems by seven compartments, five which are dynamic and two with instantaneous transfer. An internally consistent procedure for calibrating this model against an assumed initial steady state is discussed. In particular, the constraint that the average /sup 13/C//sup 12/C ratio in the total flux from the terrestrial component of the model to the atmosphere be equal to that of the steady-state atmosphere is investigated. With this additional constraint, the model provides a more accurate representation of the influence of the terrestrial system on the /sup 13/C//sup 12/C ratio of the atmosphere and provides an improved basis for interpreting records, such as tree rings, reflecting historical changes in this ratio

Spectral analysis and forest dynamics: the effects of perturbations on long-term dynamics

Long-term dynamics of forest growth and succession and the effects of environmental modification can be studied using stochastic stand growth models. The result of simulations using these models is a set of stochastic time series for stand characteristics such as total biomass. Additional analysis is generally required to clarify behavior present in the time series. In this paper spectral analysis is used to elucidate differences in dynamics of perturbed and unperturbed forest stands as evidenced by comparison of peaks in the spectral density representing various types of cyclic behavior in the total biomass of the stand. A typical Appalachian deciduous forest stand area is considered. The consequences of three types of environmental perturbations are analyzed: a blight resulting in the elimination of a dominant species, a change in average annual temperature representing the greenhouse effect of gases released to the atmosphere, and a change in the growth rate of selected tree species due to increases in the concentration of atmospheric pollutants or to acid precipitation. The stand growth model was run for each type of environmental change as well as for unperturbed conditions. Simulations were made for a 1000 year time period. The power spectral density was estimated for the total stand biomass time series using the direct method for the perturbed and unperturbed cases. The general forms of the spectral densities were different. Differences were also noted in the numbers and frequencies of specific peaks in the spectral density. An explanation is given for these differences based on tolerance characteristics, gap replacement processes and the roles of dominant tree species

Modeling the role of terrestrial ecosystems in the global carbon cycle

A model for the global biogeochemical cycle of carbon which includes a five-compartment submodel for circulation in terrestrial ecosystems of the world is presented. Although this terrestrial submodel divides carbon into compartments with more functional detail than previous models, the variability in carbon dynamics among ecosystem types and in different climatic zones is not adequately treated. A new model construct which specifically treats this variability by modeling the distribution of ecosystem types as a function of climate on a 0.5/sup 0/ latitude by 0.5/sup 0/ longitude scale of resolution is proposed

Análise florística e estrutural de uma floresta em diferentes estágios sucessionais no município de Castanhal, Pará Floristic composition and structure of a forest in different successional stages in Castanhal, Pará

O objetivo deste trabalho foi estudar a sucessão florestal pela análise florística e estrutural de floresta em três estágios sucessionais (4, 8 e 12 anos), localizadas no município de Castanhal-PA. Consideraram-se duas classes de DAP: Classe I (DAP>1cm) e classe II (DAP<1cm). Para a classe I, foram utilizadas 12 parcelas de 10m x 10m, na floresta sucessional de 12 anos e 4 parcelas de 10m x 10m nas de 4 e 8 anos. Para a classe II, foram utilizadas 48 subparcelas de 1m x 1m na floresta de 12 anos e 16 subparcelas de 1m x 1m nas de 4 e 8 anos. Na classe I, foram identificadas 18, 30 e 73 espécies e 12, 18 e 21 indivíduos/ha, respectivamente, nas florestas de 4, 8 e 12. Na classe II, foram identificadas 17, 21 e 62 espécies; e 50, 26 e 47 indivíduos/m², também, respectivamente, nas florestas de 4, 8 e 12 anos. Na classe I, Lacistema pubescens, Vismia guianensis e Myrcia silvatica apresentaram maiores abundâncias e dominâncias relativas. Na classe II, Lacistema pubescens, Vismia guianensis, Miconia ciliata, Myrcia bracteatae Banara guianensis também apresentaram elevado número de indivíduos. Myrcia silvatica apresentou maior abundância nos três estágios. A similaridade entre as floresttas na classe I foi de aproximadamente 60% e na classe II, 42%. Os resultados sugerem que as florestas apresentaram características de três fases de desenvolvimento da floresta: fase de iniciação (4 anos), fase de exclusão (8 anos) e o início da fase de reiniciação do sub-bosque (12 anos).<br>The objective of this study is to understand secondary forest succession through florisitc and structural analysis of a forest in three successional stages (4, 8 and 12 years) located in Castanhal in the state of Pará. This study considers wood species divided into two DBH classes: class I (DBH>1cm) and class II (DBH<1cm). Class I individuals were measured in twelve 10m x 10m plots in the 12-year-old successional forest, and in four 10 x 10 m plots in the 4 and 8-year-old secondary forest stands. Class II individuals were measured in 48 subplots of 1m x 1m in the 12-year-old forest stand, and in 16 subplots in the 4 and 8-year-old forest stands. In Class I, 18, 30 and 73 species were identified; and were found 12, 18 and 21 individuals/ha in the 4, 8 and 12-year-old forests, respectively. In class II, 17, 21 and 62 species were identified; and were found 50, 26 and 47 individuals/m² in the 4, 8 and 12-year-old forests, respectively. For class I, Lacistema pubescens, Vismia guianensis and Myrcia sylvatica demonstrated the greatest abundance and relative dominance. In class II, Lacistema pubescens, Vismia guianensis, Miconia ciliata, Myrcia bracteata and Banara guianensis also displayed an elevated number of individuals. Myrcia sylvatica presented the greatest abundance in the three successional stages. Similarity among plots was approximately 60% for class I and 42% for class II. The results showed the forest with three stages of successional development: initiation phase (4 years), exclusion phase (8 years), and the beginning of the understory reinitiation phase (12 years)

Effects of Fire on Landscape Heterogeneity in Yellowstone National Park, Wyoming

A map of burn severity resulting from the 1988 fires that occurred in Yellowstone National Park (YNP) was derived from Landsat Thematic Mapper (TM) imagery and used to assess the isolation of burned areas, the heterogeneity that resulted from fires burning under moderate and severe burning conditions, and the relationship between heterogeneity and fire size. About 80% of the park is covered with coniferous forests dominated by lodgepole pine (Pinus contorta var. latifolia). The majority of severely burned areas were within close proximity (50 to 200 m) to unburned or lightly burned areas, suggesting that few burned sites are very far from potential sources of propagules for plant re-establishment. Fires that occurred under moderate burning conditions early during the 1988 fire season resulted in a lower proportion of crown fire than fires that occurred under severe burning conditions later in the season. Increased dominance and contagion of burn severity classes and decrease in the edge:area ratio for later fires indicated a slightly more aggregated burn pattern compared to early fires. The proportion of burned area in different burn severity classes varied as a function of daily fire size. When daily area burned was relatively low, the proportion of burned area in each burn severity class varied widely. When daily burned area exceeded 1250 ha, the burned area contained about 50% crown fire, 30% severe surface burn, and 20% light surface burn. Understanding the effect of fire on landscape heterogeneity is important because the kinds, amounts, and spatial distribution of burned and unburned areas may influence the reestablishment of plant species on burned sites