Flammability Of Combustible Materials And Improvement On Fire Prevention Efficiency Of Urban Forests In Guangzhou City

Forest fire prevention is an important part of the construction of ecological civilization in the new era,and is also an important guarantee to promote the construction of high-quality Pearl River Delta forest city clusters and the ecological construction of Green and Beautiful Guangzhou city.However,there are numerous issues to be resolved for forests in urbanized areas,such as pure forest stand,simple forest structure,monotonous plant colors,and undefined seasonal forest landscapes,resulting in higher fire risk,lower recreational attractiveness,and lower forest ecological benefits.In this study,35 plant species and 18 stand types were selected from four urban forests in Guangzhou city.Stand characteristics and structure were obtained accurately and non-destructively by terrestrial laser scanning(TLS),and leaves and branches of different plants and surface combustibles of different stands were obtained by ground truthing and standard sampling methods.The physical and chemical properties of the leaves and branches of different plants were measured and analyzed to select excellent native fire protection plants for urban forests in Guangzhou.By dividing the forest stand combustibles into different spatial structures,the potential fire behavior and fire danger among different forest stand types were then analyzed.Determined the flammability of each stand by analyzing the characteristic structure of the stand combustibles and the physicochemical properties of the main tree species,and also classified the stands in the area into three fire risk classes.By analyzing the stand characteristics,seasonal phases of fire prevention plants,plant allocation methods and community transformation patterns of urban forests in Guangzhou,the present tended to provide theoretical support and technical reference for forest combustible management measures,fire fighting and urban forest fire prevention effectiveness,and landscape optimization in Guangzhou city and adjacent area.The main findings were listed as follows:(1)The leaves and branches of the same species differed in their physicochemical properties,with significant differences in water content,burning point,crude fat,and crude ash(p<0.05)and generally higher values were found in leaves than in branches,while calorific value was not significantly different in the two organs(p>0.05).The physicochemical properties of the same parts of different plants were significantly different(p<0.05).The fire resistance of different organs of the same plant varied.Most plants had stronger fire resistance in leaves than in branches.Among the 35 plant species,26 had stronger fire resistance in leaves than in branches,while the other nine had stronger fire resistance in branches than in leaves(i.e.:Magnolia grandiflora,Cinnamomum camphora,Michelia macclurei,Castanopsis fissa,Cunninghamia lanceolata,Viburnum odoratissimum,Acacia confusa,Carallia brachiate and Castanea henryi).(2)Combined with the fire resistance of plant leaves and branches,all the 35 plant species were ranked in the order of strength of fire resistance:Aporosa dioica,Schima superba,Sterculia lanceolate,Melastoma candidum,Ficus hirta,Vernicia montana,Carallia brachiate,Michelia macclurei,Elaeocarpus rugosus,Psychotria asiatica,Liquidambar formosana,Michelia maudiae,Melicope pteleifolia,Camellia oleifera,Viburnum odoratissimum,Castanopsis fissa,Mallotus paniculatus,Acacia auriculiformis,Schefflera octophylla,Triadica cochinchinensis,Rhodoleia championii,Acronychia pedunculate,Machilus nanmu,Acacia mangium,Gardenia jasminoides,Castanopsis chinensis,Machilus chinensis,Magnolia grandiflora,Cinnamomum camphora,Castanea henryi,Acacia confuse,Castanopsis hystrix,Eucalyptus robusta,Cunninghamia lanceolata,and Pinus massoniana.According to the results of cluster analysis,all the 35 plant species were classified into three classes:strong fire resistance,average fire resistance,and easy flammabllity.Ten plant species(Aporosa dioica,Schima superba,Sterculia lanceolate,Melastoma candidum,Ficus hirta,Vernicia montana,Carallia brachiate,Michelia macclurei,Elaeocarpus rugosus and Psychotria asiatica)were were classified into fire-resistant one,while nine plant species(Machilus chinensis,Magnolia grandiflora,Cinnamomum camphora,Castanea henryi,Acacia confuse,Castanopsis hystrix,Eucalyptus robusta,Cunninghamia lanceolate and Pinus massonian)were found to be more flammable.(3)The surface fuel load,ladder fuel load,canopy fuel load and canopy continuity were significantly different(p<0.05)among the 18 stand types in urban forest of Guangzhou.The surface fuel load of stand types ranged from 2.96 t/hm~2to 12.36 t/hm~2,and the largest stand type was 4.2 times smaller than the smallest forest type.The ladder fuel load of each stand type ranged from 0.68 t/hm~2to 6.97 t/hm~2,and the largest forest type was 10.3 times smaller than the smallest stand type.The canopy fuel load of each stand type ranged from 22.67 t/hm~2to 133.88 t/hm~2,and the largest forest type was 5.9times smaller than the smallest stand type.Canopy continuity of each forest type was 1.28～3.21,and the largest forest type was 2.5 times smaller than the smallest forest type.(4)The correlation factors of the 12 flammability types were analyzed using the principal component analysis,obtaining the flammability of 18 forest types.Overall,18stand types were ranked in order of flammability:Pinus massoniana forest,Cunninghamia lanceolata forest,mixed pine and broadleaved forest,Eucalyptus forest,mixed fir and broad forest,Acacia confuse forest,Machilus chinensis forest,Castanopsis chinensis forest,Cinnamomum camphora forest,Castanea henryi forest,Machilus nanmu forest,broadleaf mixed forest,Acacia auriculiformis forest,Schefflera octophylla forest,Liquidambar formosana forest,Elaeocarpus rugosus forest,Castanopsis fissa forest and Schima superba forest.Based on the results of cluster analysis,18 forest stands were divided into three fire risk classes,with high fire risk for Pinus massoniana forest,Cunninghamia lanceolata forest,mixed pine and broadleaved forest,Eucalyptus forest and mixed fir and broad forest.moderate fire risk for Acacia confuse forest,Machilus chinensis forest,Castanopsis chinensis forest,Cinnamomum camphora forest,Castanea henryi forest,Machilus nanmu forest and broadleaf mixed forest.and low fire risk for Acacia auriculiformis forest,Schefflera octophylla forest,Liquidambar formosana forest,Elaeocarpus rugosus forest,Castanopsis fissa forest and Schima superba forest.(5)By analyzing the stand characteristics of vegetation types and spatial distribution of combustible materials,several stand renovation measures and plant configuration optimization were proposed.Three fire prevention suggestions were also proposed to provide targeted measures to comprehensively improve the fire prevention effectiveness of woodlands.By analyzing the landscape status of different forest communities in Guangzhou,the seasonal phase of fire prevention plants,community transformation patterns and landscape plant configurations and were proposed for the local policy-makers and the researchers.These optimization measures might help to enhance the landscape effect of woodland and the ecological construction for whole city.