Fire in the Brazilian Amazon : 3. Dynamics of biomass, C, and nutrient pools in regenerating forests.

Regenerating forests have become a common land-cover type throughout the Brazilian Amazon. However, the potential for these systems to accumulate and store C and nutrients, and the fluxes resulting from them when they are cut, burned, and converted back to croplands and pastures have not been well quantified. In this study, we quantified pre- and post-fire pools of biomass, C, and nutrients, as well as the emissions of those elements, at a series of second- and third-growth forests located in the states of Pará and Rondônia, Brazil. Total aboveground biomass (TAGB) of second- and third-growth forests averaged 134 and 91 Mg ha-1, respectively. Rates of aboveground biomass accumulation were rapid in these systems, but were not significantly different between second- and third-growth forests, ranging from 9 to 16 Mg ha-1 year-1. Residual pools of biomass originating from primary forest vegetation accounted for large portions of TAGB in both forest types and were primarily responsible for TAGB differences between the two forest types. In second-growth forests this pool (82 Mg ha-1) represented 58% of TAGB, and in third-growth forests (40 Mg ha-1) it represented 40% of TAGB. Amounts of TAGB consumed by burning of second- and third-growth forests averaged 70 and 53 Mg ha-1, respectively. Aboveground pre-fire pools in second- and third-growth forests averaged 67 and 45 Mg C ha-1, 821 and 707 kg N ha-1, 441 and 341 kg P ha-1, and 46 and 27 kg Ca ha-1, respectively. While pre-fire pools of C, N, S and K were not significantly different between second- and third-growth forests, pools of both P and Ca were significantly higher in second-growth forests. This suggests that increasing land use has a negative impact on these elemental pools. Site losses of elements resulting from slashing and burning these sites were highly variable: losses of C ranged from 20 to 47 Mg ha-1; N losses ranged from 306 to 709 kg ha-1; Ca losses ranged from 10 to 145 kg ha-1; and P losses ranged from 2 to 20 kg ha-1. Elemental losses were controlled to a large extent by the relative distribution of elemental mass within biomass components of varying susceptibilities to combustion and the temperatures of volatilization of each element. Due to a relatively low temperature of volatilization and its concentration in highly combustible biomass pools, site losses of N averaged 70% of total pre-fire pools. In contrast, site losses of P and Ca resulting from burning were 33 and 20% of total pre-fire pools, respectively, as much of the mass of those elements was deposited on site as ash. Pre- and post-fire biomass and elemental pools of second- and third-growth forests, as well as the emissions from those systems, were intermediate between those of primary forests and pastures in the Brazilian Amazon. Overall, regenerating forests have the capacity to act as either large terrestrial sinks or sources of C and nutrients, depending on the course of land-use patterns within the Brazilian Amazon. Combining remote sensing techniques with field measures of aboveground C accumulation in regenerating forests and C fluxes from those forests when they are cut and burned, we estimate that during 1990-1991 roughly 104 Tg of C was accumulated by regenerating forests across the Brazilian Amazon. Further, we estimate that approximately 103 Tg of C was lost via the cutting and burning of regenerating forests across the Brazilian Amazon during this same period. Since average C accumulations (5.5 Mg ha-1 year-1) in regenerating forests were 19% of the C lost when such forests are cut and burned (29.3 Mg ha-1), our results suggest that when less than 19% of the total area accounted for by secondary forests is cut and burned in a given year, those forests will be net accumulators of C during that year. Conversely, when more than 19% of regenerating forests are burned, those forests will be a net source of C to the atmosphere.

Fire in the Brazilian Amazon 2. Biomass, nutrient pools and losses in cattle pastures.

Conversion to cattle pasture is the most common fate of the ≈426,000 km2 of tropical forest that has been deforested in the Brazilian Amazon. Yet little is known about the biomass, C, nutrient pools, or their responses to the frequent fires occurring in these pastures. We sampled biomass, nutrient pools and their losses or transformation during fire in three Amazonian cattle pastures with typical, but different, land-use histories. Total aboveground biomass (TAGB) ranged from to 53 to 119 Mg ha-1. Residual wood debris from the forests that formally occupied the sites composed the majority of TAGB (47-87%). Biomass of fine fuels, principally pasture grasses, was ≈16-29 Mg ha-1. Grasses contained as much as 52% of the aboveground K pool and the grass and litter components combined composed as much as 88% of the aboveground P pool. Fires consumed 21-84% of the TAGB. Losses of C to the atmosphere ranged from 11 to 21 Mg ha-1 and N losses ranged from 205 to 261 kg ha-1. Losses of S, P, Ca, and K were <33 kg ha-1. There were no changes in surface soil (0-10 cm) nutrient concentration in pastures compared to adjacent primary forests. Fires occur frequently in cattle pastures (i.e., about every 2 years) and pastures are now likely the most common type of land burned in Amazonia. The first 6 years of a pastures existence would likely include the primary forest slash fire and three pasture fires. Based upon our results, the cumulative losses of N from these fires would be 1935 kg ha-1 (equivalent to 94% of the aboveground pool of primary forest). Postfire aboveground C pools in old pastures are as low as 3% of those in adjacent primary forest. The initial primary forest slash fire and the repeated fires occurring in the pastures result in the majority of aboveground C and nutrient pools being released via combustion processes rather than decomposition processes.

Acute manifestations and neurologic sequelae of Epstein-Barr virus encephalitis in children.

BACKGROUND: Complications of Epstein-Barr virus (EBV) infection are diverse and include a number of neurologic manifestations such as meningitis, meningoencephalitis, cerebellitis, cranial neuritis and others. In general encephalitis caused by EBV in pediatric patients has been considered a self-limited illness with few or no sequelae. METHODS: Charts were reviewed from all patients < 18 years of age admitted to or discharged from the State University of New York Health Science Center at Syracuse between 1982 and 1992 with a diagnosis of encephalitis or meningo-encephalitis. Eleven cases of EBV encephalitis diagnosed during a 10-year period were reviewed to characterize the clinical and laboratory findings in the acute setting and the extent of neurologic sequelae on follow-up. RESULTS: Acute neurologic manifestations were diverse and included combative behavior (55%), seizures (36%), headache (36%) and evidence of focal involvement (27%). Classic findings of infectious mononucleosis were noted infrequently; 18% each had pharyngitis, adenopathy, positive heterophile antibody tests or atypical lymphocytosis. Two patients (18%) had abnormal neuroimaging studies, one in the acute stage and the other at the time of follow-up. Seven patients (64%) had abnormal electroencephalograms (EEGs) in the acute setting; of these three had persistent abnormalities on follow-up. Forty percent developed persistent neurologic abnormalities including global impairment, perseverative autistic-like behavior and persistent left upper extremity paresis. CONCLUSIONS: Classic signs, symptoms and laboratory findings in infectious mononucleosis may be absent in Epstein-Barr virus encephalitis. Neurologic sequelae occur in a substantial number of patients.

Fire in the Brazilian Amazon: 1. Biomass, nutrient pools, and losses in slashed primary forests.

Deforestation in the Brazilian Amazon has resulted in the conversion of >230,000 km2 of tropical forest, yet little is known on the quantities of biomass consumed or the losses of nutrients from the ecosystem. We quantified the above-ground biomass, nutrient pools and the effects of biomass burning in four slashed primary tropical moist forests in the Brazilian Amazon. Total above-ground biomass (TAGB) ranged from 292 Mg ha-1 to 436 Mg ha-1. Coarse wood debris (>20.5 cm diameter) was the dominant fuel component. However, structure of the four sites were variable. Coarse wood debris comprised from 44% to 69% of the TAGB, while the forest floor (litter and rootmat) comprised from 3.7 to 8.0% of the TAGB. Total biomass consumption ranged from 42% to 57%. Fires resulted in the consumption of >99% of the litter and rootmat, yet <50% of the coarse wood debirs. Dramatic losses in C, N, and S were quantified. Lesser quantities of P, K, and Ca were lost by combustion processes. Carbon losses from the ecosystem were 58-112 Mg ha-1. Nitrogen losses ranged from 817 to 1605 kg ha-1 and S losses ranged from 92 to 122 kg ha-1. This represents losses that are as high as 56%, 68%, and 49% of the total above-ground pools of these nutrients, respectively. Losses of P were as high as 20 kg ha-1 or 32% of the above-ground pool. Losses to the atmosphere arising from primary slash fires were variable among sites due to site differences in concentration, fuel biomass, and fuel structure, climatic fluctuations, and anthropogenic influences. Compared to fires in other forest ecosystems, fires in slashed primary tropical evergreen forests result in among the highest total losses of nutrients ever measured. In addition, the proportion of the total nutrient pool lost from slash fires is higher in this ecosystem compared to other ecosystems due to a higher percentage of nutrients stored in above-ground biomass.