A Study On The Relation Between The Decline Disease Of Pinus Sylvestris Var.mongolica And Forest Combustibility In Honghuaerji

Pinus sylvestris var.mongolica Litv.belongs to Pinaceae,Pinoideae,Pinus.Its wood is loose.Branches,leaves and cones contain a lot of resin and volatile oils,which are highly flammable,leading the risk of forest fire is increased.In recent years,the phenomena of bark cracking and oil outflow have appeared in Pinus sylvestris var.mongolica Litv.forests on the sandy land.The study took the Pinus sylvestris var.mongolica Litv.forest in Honghua Eiji of Inner Mongolia as the research object,the typical diseased stands were selected.The bark of Pinus sylvestris var.mongolica Litv.with oil was sampled separately from the healthy bark as the control.The oil content of Pinus sylvestris var.mongolica Litv.was determined by organic solvent extraction method.The composition content of Pinus sylvestris var.mongolica Litv.was determined by referring to the national industry standard.The significances were analysis by the statistics software.The specific results are as follows:1.Through indoor and outdoor investigation and experiments,it is determined that the disease is a kind of forest recession disease,which is caused by the combination of abiotic factors such as climate,soil and biological factors invaded in the later stage,resulting in a significant decline in the growth potential of trees and eventually leading to death.The morbidity was 91.7%,and the disease index was 33?61.1.2.Six fungi,Alternaria,Fusarium,Rhizopus,Tolura,Chaetomium and Sphaeropsis,were isolated from phloem and skin of decaying wood,healthy wood and twigs.Sporospora were isolated both from decaying wood and healthy wood.3.The trunk analysis data of declining trees and healthy trees showed that the volume,DBH and height growth of declining trees were lower than that of healthy trees,and the growth of declining trees was lower than that of healthy trees.At 40-year-old,the annual volume growth of declining trees decreased by 16.0%compared with that of healthy trees,and the annual volume growth of declining trees decreased by 17.9%.4.The water content,organic solvent extract content and alkali extract content of decayed wood bark increased,ash content and holocellulose content decreased,and the content of pentosan,acid-soluble lignin,acid-insoluble lignin and lignin did not change significantly.Principal component analysis showed that water,ash,organic solvent extract,alkali extract,synthetic fiber,lignin and acid-insoluble lignin were the first principal components,and acid-soluble lignin was the second principal component.5.The oil content in the bark of declined trees is about 6 times that of healthy trees,and the statistical test shows that the difference is very significant.This indicated that the oil content in the bark of Pinus sylvestris var.mongolica increased greatly because of the flowing fat.Promote its evolution into flammable forest,increase the possibility of fire and flammability,once a fire occurs,it is very easy to trigger trunk fire and crown fire..6.The ignition time of decayed bark and healthy bark were 6.00 s(± 1.73)and 22.67 s(±1.15),respectively.Oil reduces ignition time by nearly four times,which in turn makes decaying wood easier to burn.The heat release rate curves(HRR)of decaying wood and healthy wood are parabolic and have peaks,225.19 kW/m2 and 75.27 kW/m2,respectively.7.Pearson correlation analysis between bark composition and fire occurrence index showed that water,organic extracts and alkali extracts were negatively correlated with fire occurrence index,and the correlation coefficients were-0.995,-0.998 and-0.999,respectively,while ash,brown cellulose,lignin and acid-insoluble lignin were positively correlated with fire occurrence index,and the correlation coefficients were 0.978,0.999,0.975 and 0.994,respectively.