Pyrolysis Characteristics Of Main Tree And Shrub Species In Da Xing’an Mountains

Forest fires are an important factor in disturbing forest ecosystems.On the one hand,controlled forest fires are beneficial to forest ecosystem succession,while on the other hand,uncontrolled forest fires can have negative effects on forest organisms.Forest fires require the interaction of forest combustibles,fire source and oxygen to form,and forest combustibles are the basis of forest fire occurrence.Thermogravimetric analysis is an important method to study the pyrolysis process of forest combustibles and their potential combustibility.Therefore,exploring the pyrolysis parameters of bark,branches and leaves of major tree and shrub species in Tahe area of the Da Xing’an Mountains,and ranking the pyrolysis kinetic parameters in terms of their combustibility,exploring the degree of influence on forest fires,and determining the basis for the selection of forest fire species and the establishment of corresponding forest fire behaviour models are of profound significance for forest fire prevention and suppression.In this research,the bark and leaves of 12 trees（Quercus mongolica,Larix gmelinii,Betula dahurica,Betula platyphylla,Populus suaveolens,Salix arbutifolia,Populus davidiana,Alnus sibirica,Sorbus alnifolia,Picea jezoensis var.microsperma,Picea koraiensis）and the branches and leaves of 7 shrubs（Lespedeza bicolor,Juniperus sabina var.davurica,Corylus heterophylla,Pinus pumila,Rhododendron tomentosum,Vaccinium uliginosum,Vaccinium vitis-idaea）in Tahe County,Da Xing’an Mountains,Heilongjiang Province,were used to obtain the pyrolysis kinetics using a thermogravimetric analysis instrument.The corresponding parameters were obtained as the activation energy and pre-exponential facto.The activation energy as well as the pyrolysis parameters of different parts of the main trees and shrubs were analyzed for combustibility.The main results of the study obtained are as follows:The activation energies of tree bark ranged from 4.342 to 8.601 kJ·mol^-1and leaves ranged from 3.956 to 10.226 kJ·mol^-1;the activation energies of shrub branches ranged from3.832 to 8.258 kJ·mol^-1and shrub leaves ranged from 4.238 to 6.635 kJ·mol^-1.The trends of TG and DTG curves during pyrolysis were basically the same for trees and shrubs.In the first stage of water loss,it could be found that the water content of shrubs was lower than that of trees,indicating that trees were less likely to be ignited compared to shrubs.The second stage is the heterocellulose pyrolysis stage,which is also the main weight loss stage caused by the pyrolysis reaction.The intensity of reaction in this stage was basically the same for flame combustion of trees and shrubs.The four-dimensional combustibility ranking revealed that the best ignition,vigor and persistence of shrub bark was that of Pinus pumila,and the best ignition,persistence and consumption of shrub leaves was also that of Pinus pumila,indicating that among shrubs Pinus pumila belongs to the flammable species.And the combined ranking by principal component analysis method and pyrolysis kinetics found that the lowest combustibility and better fire resistance of Salix arbutifolia.