A comparison of charcoal measurements for reconstruction of Mediterranean paleo-fire frequency in the mountains of Corsica

Fire-history reconstructions inferred from sedimentary charcoal records are based on measuring sieved charcoal fragment area, estimating fragment volume, or counting fragments. Similar fire histories are reconstructed from these three approaches for boreal lake sediment cores, using locally defined thresholds. Here, we test the same approach for a montane Mediterranean lake in which taphonomical processes might differ from boreal lakes through fragmentation of charcoal particles. The Mediterranean charcoal series are characterized by highly variable charcoal accumulation rates. Results there indicate that the three proxies do not provide comparable fire histories. The differences are attributable to charcoal fragmentation. This could be linked to fire type (crown or surface fires) or taphonomical processes, including charcoal transportation in the catchment area or in the sediment. The lack of correlation between the concentration of charcoal and of mineral matter suggests that fragmentation is not linked to erosion. Reconstructions based on charcoal area are more robust and stable than those based on fragment counts. Area-based reconstructions should therefore be used instead of the particle-counting method when fragmentation may influence the fragment abundance.

Study on Rock Mass Fragment Size Prediction Technology Based on Three-Dimensional Interception Model

Based on the law of the spatial distribution, using Monte Carlo technology to simulate joint system, and using three-dimensional solid cutting techniques to build a new rock mass fragmentation prediction model of block three-dimensional interception model. Based on consideration in the joint continuity and the mechanical properties of rock mass, the model simulated the spatial distribution of structure planes according to statistical principles, and predicted rock mass fragmentation using structure planes to cut model prototype and ultimately formed a block muster consisting of cutting blocks. Then, according to a new method of the block shape classification, the distribution statistic rule of internal entities rock block, which are cut out by the structure planes, size and shape are studied. The simulation results show that the fragments with equivalent size of more than 1.65 m account for 40 per cent and those more than 1.26 m account for 59.85 per cent of the total fragment volume.

The regenerative capacity of root cuttings of Taraxacum officinale under natural conditions

Plants of Taraxacum officinale Weber were grown from the seeds of a single parent. At monthly intervals during two successive growing seasons, and commencing [Formula: see text] months after germination in June 1974, randomly selected plants were excavated and the roots divided into 2 cm long fragments. Fragments were replanted at different depths and in different orientations.Percentage survival (regeneration and survival for at least 4 months) displayed seasonal variation with a minimum of 5–32% survival for fragments obtained in May 1975 at the time of maximum flowering of the source plants and for very young fragments obtained in the first treatment in July 1974. The highest percentage survival, 60–100%, occurred for fragments obtained in the second growing season from June to September, inclusive. Weather conditions appear to exert a significant effect on the magnitude of the flowering response, but not the timing of the spring flowering peak.Regenerative capacity declined consistently down the length of the root in relation to a concomitant decrease of fragment volume, but increased with respect to age for cuttings of a given volume. Rotation of cuttings away from the normal planting orientation resulted in a decline in percentage survival, and an increase in regeneration time. Depth of planting down to 10 cm did not consistently influence either percentage survival or time for regeneration.The time taken for regeneration was largely dependent on climate, with fragments planted in September 1974 regenerating most quickly (an average of 20 days), and fragments obtained in October 1974 taking the longest time to regenerate (174 days). In addition, time for regeneration was positively correlated with fragment volume. These results show that under natural conditions survival of fragments is not independent of season, and is significantly lower than 100% as previously reported from laboratory studies of regeneration.