Carbon distribution and combustibility of fuels in Larix olgensis plantations.

In order to study the interaction between fuel carbon storage (CS) distribution and combustibility of plantation ecosystem at different stages in depth, and evaluate forest fire risk grade comprehensively, the carbon storages and distribution of Larix olgensis plantations at five different stages from 7 to 48 years old were compared in representative region of Lesser Khingan Mountains (Northeast of China). First, fuels were divided into five subtle layers according to their virtual structure. Then, fuel carbon storage of each layer was estimated by DBH, height, crown area, depth, etc. , via corresponding carbon density. Finally, the fire classes, fire behavior, and fire risk of each layer at different stages were analyzed, and evaluated the forest combustibility based on the total fuel carbon. The results showed that: 1) Surface fire of immature forest can be ignited easily because of abundant herbs, and high鄄intensity crown fire could occur, but its spread rate was low because of less CS as 87郾660 t/ hm2; 2) Once crown fire occur in juvenile forest (with 138郾574 t/ hm2 CS), high density and certain dead branches would result in high鄄 intensity crown fire; 3) Because of tending and thinning, middle鄄aged stand with 163郾884 t/ hm2 CS had lower probability of surface or crown fire, but it can initiate crown fire with high spread rate once fire was ignited; 4) In near鄄mature stand (with 199郾838 t/ hm2 CS), crown fire initiation only occurs under extreme conditions, but can be on moderate鄄intensity surface fire with more possibility. 5) A mass of fuel as high as 253郾962 t/ hm2 CS could result in high鄄intensity surface fire in mature stand without effective reduction treatments to floor fuel.