Natural Forest Fires Research Articles

LATE HOLOCENE FIRE AND AGRICULTURE IN THE COPAN VALLEY, HONDURAS

Pollen and charcoal analysis of a 5.3-m sediment core from Aguada Petapilla, a peat bog, provides evidence of late Holocene vegetation and fire history in the Copan Valley, Honduras. Low concentration and preservation problems characterized the pollen flora, but there are taxa present indicative of major agricultural trends, including Zea mays. Microscopic charcoal fragments are well represented and record continued burning in the region since the lowest level of the core (5700 B.P. [3750 B.C.]). Presence of Zea indicates that maize farming was initiated by as early as 2300 B.C. Three peaks in charcoal-fragment frequencies occur in periods centered approximately at 900 B.C., 400 B.C., and A.D. 600. Fires in this relatively dry region of the southern Maya Lowlands (whose mean annual rainfall is about 1,400 mm) could have resulted from natural forest fires or human agricultural clearing at any time in the Holocene. This contrasts with wetter areas of tropical Central and South America (mean annual rainfall of about 2,500–4,000 mm) where significant climatic drying is required to ignite primary tropical forest.

Influence of catchment deforestationby logging and natural forest fires on crustacean community size structure in lakes of the Eastern Boreal Canadian forest

Logging and wildfires are important perturbation factors of the Canadian Boreal forest, but their effects on aquatic communities remain largely unknown. Here, we assess the ecological effects of logging and wildfires on aquatic communities, based on changes in crustacean zooplankton size spectra among logged, burnt and unperturbed lakes of the Canadian Precambrian Boreal Shield. A laboratory version of the Optical Particle Counter (OPC-1L) was used to establish the crustacean size spectra of zooplankton samples collected in 38 lakes characterized by different catchment conditions: logged in 1995 (nine 'logged' lakes); burnt in 1995 (nine 'burnt' lakes); left unperturbed over the past 70 years (20 reference lakes). Size spectra are characterized by crustacean biovolume in 22 size classes, from 200-300 μm equivalent spherical diameter (ESD) to 2300-2400 μm ESD. Size spectra in logged and burnt lakes were on average shifted towards larger size classes relative to reference lakes, although the reference and burnt groups of lakes were the only pair statistically different from one another (at a = 5%). As a result, biovolume of crustacean organisms >1100 μm ESD in burnt lakes was on average higher by 366 and 388%, respectively, 1 and 2 years following catchment perturbations relative to reference lakes. Among a set of 15 water quality variables and 14 fish species density variables, potassium concentration and white sucker density were the most important environmental correlates of crustacean size structure.

Assessing the naturalness of boreal forests in eastern Fennoscandia

This study aims to define the level of naturalness in the protected forests of eastern Fennoscandia, i.e. to determine how natural or semi-natural are the currently protected and unmanaged forests, and the extent to which the past human influence has affected the current forest structure. The plots used in the study represent both currently unmanaged and managed forests. The unmanaged forests are located in nature protection areas. We have used data from earlier forest inventories, determined by the visual estimation of compartments, together with the measured stand variables. The data cover detailed analysis of 79 forest sites or stands in both in mesic and sub-xeric forests. The whole successional gradient is included in the data. In unmanaged forests, fellings have occurred on 39% of the sample plots in sub-xeric areas, and on 28% of the sample plots in mesic areas. According to the historical records 33% of all the unmanaged forests have definitely been (selectively) felled, 21% possibly, and 46% show no signs of fellings. In general, the unmanaged forests in eastern Finland bear ample evidence of light selection felling. Thus, these stands could better be regarded as semi-natural rather than natural forests. Mesic old-growth stands are less affected (73% are completely untouched), but the tree volume data, number of tree storeys and the signs of slash-and-burn cultivation are nevertheless clear evidence of the impact of human activities. The growing intensity of human activities since the 1950s can also be seen in semi-natural succession forests as the presence of cut stumps and the probability of felling in young stages. Real natural/semi-natural sapling and young forests are very rare and occur only in Russia. The diameter distribution in semi-natural sapling and young forests with reverse J-shaped distributions showed considerably greater variation. Also the mature and old-growth, semi-natural forests were characterised by the decrease in reverse J-shaped distributions. The timber volume in stands was generally lower at the beginning of the 20th century. Overall, the forests in nature reserves are structurally rather different to those growing at the beginning of the 20th century, and show patterns not typical of natural forests. The slash-and-burn agriculture practised during the 1800s and earlier has profoundly affected the natural spatial and temporal disturbance regimes, with clear consequences for the current tree species and age composition. More recent deviations from the natural forest structures are, however, largely due to the absence of natural and anthropogenic forest fires during the 1900s.

Self-organization, the cascade model, and natural hazards.

We consider the frequency-size statistics of two natural hazards, forest fires and landslides. Both appear to satisfy power-law (fractal) distributions to a good approximation under a wide variety of conditions. Two simple cellular-automata models have been proposed as analogs for this observed behavior, the forest fire model for forest fires and the sand pile model for landslides. The behavior of these models can be understood in terms of a self-similar inverse cascade. For the forest fire model the cascade consists of the coalescence of clusters of trees; for the sand pile model the cascade consists of the coalescence of metastable regions.

In situ charcoal fragments as remains of natural wild fires in the upper Würm of the Carpathian Basin

Charcoal layers were found in loess layers of the Younger Würm period, at 11 localities around Kopasz Hill, Tokaj, in the Carpathian Basin. Detailed sedimentological, geochemical, radiocarbon, palaeontological and anthracological investigations show that Picea-containing taiga forest–steppe habitats existed on the area between 29,000 and 21,000 years BP, on the basis of radiocarbon measurements. These forests fell victim to extensive fires that seem to have spread across the basin. This fact is supported by the characteristic macro- and microstructure of the charred remains, using SEM identification and thermoanalytical examination. The firing temperature was 600–700°C, suggesting a natural forest fire. Fire scars can also be observed on the remains, as well as the burnt sediment forming a silhouette (the so-called burning court) of the fallen trunks or roots. Thus, these fragments have remained in their in situ position.

Potential causes of differences between ground and surface air temperature warming across different ecozones in Alberta, Canada

Analysis and modelling of temperature anomalies from 25 selected deep wells in Alberta show that the differences between GST (ground surface temperature) warming for the northern Boreal Forest ecozone and the combined Prairie Grassland ecozone and Aspen Parkland transition region to the south occur during the latter half of this century. This corresponds with recent changes in surface albedo resulting from permanent land development in the northern areas and also to increases in natural forest fires in the past 20 years. Differences between GST and SAT (surface air temperature) warming are much higher in the Boreal Forest ecozone than in the Prairie Grassland ecozone and Aspen Parkland transition region. Various hypotheses which could account for the existing differences between the GST and SAT warming in the different ecozones of Alberta, and western Canada in general, are tested. Analysis of existing data on soil temperature, hydrological piezometric surfaces, snowfall and moisture patterns, and land clearing and forest fires, indicate that large areas of Alberta, characterised by anomalous GST warming, have experienced widespread changes to the surface landscape in this century. It is postulated that this has resulted in a lower surface albedo with a subsequent increase in the absorption of solar energy. Heat flow modelling shows that, after climatic SAT warming, permanent clearing of the land is the most effective and likely cause of the observed changes in the GST warming. The greater GST warming in the Boreal Forest ecozone in the latter half of this century is related to landscape change due to land development and increasing forest fire activity. It appears to account for a portion of the observed SAT warming in this region through a positive feedback loop with the overlying air. The anthropogenic effect on regional climatic warming through 20th century land clearing and landscape alteration requires further study. In future, more accurate quantification of these various forcings will be necessary in order to distinguish between, and to detect, the variety of natural and anthropogenic influences and on climate.

Palaeogeographic significance of black pebbles (Lower Cretaceous, Prebetic, southern Spain)

The presence of black pebbles in carbonate stratigraphic sections constitutes a criterion for identifying emergence episodes, which are significant to palaeographic reconstructions and to location of sedimentary cycle boundaries. Three genetic models can be inferred from the stratigraphic, petrologic and geochemical study of black pebbles that occur in sediments of the Lower Cretaceous of the Prebetic (southern Spain). In the first model, black pebbles are the product of redeposition in tidal and lacustrine environments from layers rich in organic matter (carbonaceous layers). In the second model, blackening takes place as a result of very mature organic matter, mainly generated from terrestrial plants (possibly burnt ones), selectively staining some of the intraclasts of the storm layers in intertidal environmnts. In the third model, applicable only to pedogenic and lacustrine environments, black pebbles, to a large extent, originate from a redeposition of pedogenic carbonate materials affected by natural forest fires, where blackening was caused by a sudden and rapid increase in temperature. The third hypothesis is supported by data obtained from an experiment in which samples underwent progressive heating to monitor the blackening process and accompanying change in isotopic composition. In all cases, the effects of storms and/or currents and waves caused erosion and redeposition.

Natural rain forest fires in Eastern Borneo during the Pleistocene and Holocene

Natural rain forest fires in Eastern Borneo during the Pleistocene and Holocene

Measurements of Cloud Condensation Nuclei and Cloud Droplet Size Distributions in the Vicinity of Forest Fires

Abstract Airborne measurements of cloud condensation nuclei (CCN) were made in the vicinity of a planned burn of natural forest products. The concentrations of CCN, active at 0.5% supersaturation, reached a peak value of 5000 cm−3 about 38 km downwind of the fire, compared to concentrations of 250–500 cm−3 upwind. It is estimated that 6 × 1010 CCN were produced per gram of wood consumed.On another occasion the microstructure of small cumulus clouds were measured in the vicinity of a natural forest fire. The droplet size distributions were narrower and the concentrations of droplets higher in two clouds situated in the plume from the fire than in two clouds upwind of the plume.

Ice Nuclei from a Natural Forest Fire

Ice Nuclei from a Natural Forest Fire