Fuel load characterisation and quantification for the development of fuel models for Pinus patula in South Africa

[摘要] ENGLISH ABSTRACT: The characteristics and total fuel load of the forest floor (FF) and harvest residue (HR) areneeded to develop tools that can be used for fuel load management, fire risk analysis andfire behaviour prediction for P. patula grown in the summer rainfall area of South Africa (SA).Forest floor depth, mass and ash-free mass were measured and there was generally agreater range in depth under sawtimber (ST) stands than under pulpwood (PLP) stands.Forest floor loads, prior to ashing, ranged from 21 - 168 t ha-1 and 27 - 72 t ha-1, for ST andPLP stands, respectively and loads increased linearly with stand age. Sawtimber and PLPstands were analysed together, which resulted in a significant correlation between depth andmass (r2 = 0.78, n = 31). A loss on ignition procedure carried out on sub-samples of the FFimproved the relationship between the FF depth and the ash-free mass for the differentstands, and provided a more accurate model for the prediction of mass from depth. Amultiple regression analysis revealed that age, altitude and mean annual precipitation (MAP)provided the best subset and accounted for 72% of the variation in the FF mass observed.The effect of increasing FF load and increasing moisture content on the fireline intensity(FLI) was examined using the fire behaviour prediction programme, BehavePlus.Harvest residue was quantified and characterised in terms of fuel size classes, under currentsilvicultural regimes for ST and PLP, for the development of fuel models for this species overits planted range in SA. An investigation into the proportion (by mass) of the 1- (0.0 - 0.6cm), 10- (0.6 – 2.5 cm), 100- (2.5 – 7.6 cm) and 1000-hr (> 7.6 cm diameter) fuel classes ofthe total HR mass indicated that there was a significant difference between the mass of the1-, 10- and 1000-hr fuel classes of the two silvicultural regimes, and no significant differencefor the 100-hr fuel class. Two fuel models for P. patula HR and two models for standingtimber were developed using the new model (NEWMDL) programme of BEHAVE and testedin BehavePlus.Nutrient concentrations were used with FF layer and HR size class load data to estimate thequantities of nutrients held in the fuel and to describe nutrient distributions in the fuelcomplex. Significant differences in the nutrient concentration of the FF layers and fuelcomponents were observed which has important implications for fuel management. Theconcentration of N determined in this study, relative to that determined in other similarstudies on P. patula was low. Forest floor loads were predicted and nutrient pools calculatedfor typical ST and PLP stands at both low and high altitude to provide insight into the nutrientdistributions within the fuel complex.

[发布机构] Stellenbosch University