Drought-induced Amazonian wildfires instigate a decadal-scale disruption of forest carbon dynamics

Drought-induced wildfires have increased in frequency and extent over the tropics. Yet, the long-term (greater than 10 years) responses of Amazonian lowland forests to fire disturbance are poorly known. To understand post-fire forest biomass dynamics, and to assess the time required for fire-affected forests to recover to pre-disturbance levels, we combined 16 single with 182 multiple forest census into a unique large-scale and long-term dataset across the Brazilian Amazonia. We quantified biomass, mortality and wood productivity of burned plots along a chronosequence of up to 31 years post-fire and compared to surrounding unburned plots measured simultaneously. Stem mortality and growth were assessed among functional groups. At the plot level, we found that fire-affected forests have biomass levels 24.8 ± 6.9% below the biomass value of unburned control plots after 31 years. This lower biomass state results from the elevated levels of biomass loss through mortality, which is not sufficiently compensated for by wood productivity (incremental growth + recruitment). At the stem level, we found major changes in mortality and growth rates up to 11 years post-fire. The post-fire stem mortality rates exceeded unburned control plots by 680% (i.e. greater than 40 cm diameter at breast height (DBH); 5-8 years since last fire) and 315% (i.e. greater than 0.7 g cm^-3 wood density; 0.75-4 years since last fire). Our findings indicate that wildfires in humid tropical forests can significantly reduce forest biomass for decades by enhancing mortality rates of all trees, including large and high wood density trees, which store the largest amount of biomass in old-growth forests. This assessment of stem dynamics, therefore, demonstrates that wildfires slow down or stall the post-fire recovery of Amazonian forests.This article is part of a discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.

The Amazon basin in transition

Agricultural expansion and climate variability have become important agents of disturbance in the Amazon basin. Recent studies have demonstrated considerable resilience of Amazonian forests to moderate annual drought, but they also show that interactions between deforestation, fire and drought potentially lead to losses of carbon storage and changes in regional precipitation patterns and river discharge. Although the basin-wide impacts of land use and drought may not yet surpass the magnitude of natural variability of hydrologic and biogeochemical cycles, there are some signs of a transition to a disturbance-dominated regime. These signs include changing energy and water cycles in the southern and eastern portions of the Amazon basin.

Forest structure and carbon dynamics in Amazonian tropical rain forests

Living trees constitute one of the major stocks of carbon in tropical forests. A better understanding of variations in the dynamics and structure of tropical forests is necessary for predicting the potential for these ecosystems to lose or store carbon, and for understanding how they recover from disturbance. Amazonian tropical forests occur over a vast area that encompasses differences in topography, climate, and geologic substrate. We observed large differences in forest structure, biomass, and tree growth rates in permanent plots situated in the eastern (near Santarém, Pará), central (near Manaus, Amazonas) and southwestern (near Rio Branco, Acre) Amazon, which differed in dry season length, as well as other factors. Forests at the two sites experiencing longer dry seasons, near Rio Branco and Santarém, had lower stem frequencies (460 and 466 ha(-1) respectively), less biodiversity (Shannon-Wiener diversity index), and smaller aboveground C stocks (140.6 and 122.1 Mg C ha(-1)) than the Manaus site (626 trees ha(-1), 180.1 Mg C ha(-1)), which had less seasonal variation in rainfall. The forests experiencing longer dry seasons also stored a greater proportion of the total biomass in trees with >50 cm diameter (41-45 vs 30% in Manaus). Rates of annual addition of C to living trees calculated from monthly dendrometer band measurements were 1.9 (Manaus), 2.8 (Santarém), and 2.6 (Rio Branco) Mg C ha(-1) year(-1). At all sites, trees in the 10-30 cm diameter class accounted for the highest proportion of annual growth (38, 55 and 56% in Manaus, Rio Branco and Santarém, respectively). Growth showed marked seasonality, with largest stem diameter increment in the wet season and smallest in the dry season, though this may be confounded by seasonal variation in wood water content. Year-to-year variations in C allocated to stem growth ranged from nearly zero in Rio Branco, to 0.8 Mg C ha(-1) year(-1) in Manaus (40% of annual mean) and 0.9 Mg C ha(-1) year(-1) (33% of annual mean) in Santarém, though this variability showed no significant relation with precipitation among years. Initial estimates of the C balance of live wood including recruitment and mortality as well as growth suggests that live wood biomass is at near steady-state in Manaus, but accumulating at about 1.5 Mg C ha(-1) at the other two sites. The causes of C imbalance in living wood pools in Santarém and Rio Branco sites are unknown, but may be related to previous disturbance at these sites. Based on size distribution and growth rate differences in the three sites, we predict that trees in the Manaus forest have greater mean age (approximately 240 years) than those of the other two forests (approximately 140 years).

The inferiorly based pharyngoplasty: effects on chronic otitis media with effusion

Conflicting reports in the literature on the relationship between the inferiorly based pharyngeal flap and otitis media with effusion (OME) motivated a prospective study on 51 children between 3 and 12 years of age suffering from velopharyngeal incompetence. The patient group consisted of 34 children with cleft palate and 17 children with congenitally short palate. The male-female ratio was 37 to 14, showing no differences regarding physical disability. Each child underwent an inferiorly based pharyngoplasty. Repeated otoscopic, tympanometric, and audiometric examinations revealed that prior to pharyngoplasty half of the patients had bilateral chronic OME related to a conductive hearing loss of 30 to 35 dB. The disease was most frequently found in children with cleft palate (p less than 0.001) and in children less than 6 years of age (p less than 0.05). Bilateral chronic OME was independent of the type and side of cleft. Within 3 months of pharyngoplasty, a 60-percent decrease in the frequency of bilateral chronic OME was found. Children older than 6 years of age had most benefit with respect to OME (p less than 0.05). The biomechanical basis of the relationship between the pharyngeal flap and eustachian tube is discussed, focused on retropositioning of the levator muscle sling and reduced oronasal air leakage.

Management of fingernail deformities after thermal injury

Fingernail deformities after thermal injury can be very disfiguring and troublesome. The fingernails may be discoloured, cleft or vertically deviated. From the pathophysiology of the nail growth in general, the specific features of the nail deformities after deep burn can be deduced, as can guidelines for the treatment. Over a two-year period, 153 patients with burned hands were treated in the Groningen Burn Centre. Seven of these patients developed abnormal quality and growth pattern of the fingernails. In two patients an effort was made to correct the deformity by incising the dorsal skin at the base of the nail fold, reflecting the nail fold and covering the acquired defect with a full thickness skin graft. Although the patients were satisfied with the results achieved, one year after the operation little or no improvement in the nail growth was found. A cautious policy should be followed in correcting these deformities, since dislocation of the eponychium together with damage to the nail matrix and the nail bed play a complex role in the process of deformation.