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2.1 Type, Duration and Occurrence

Forest fires in Thailand annually occur during the dry season from December to May with their peak in February-March. Fires, Mostly classified as surface fires, mainly take place in; Mixed Deciduous Forest, Dry Dipterocarp Forest, and Forest Plantations, and to some extent in Dry Evergreen Forest, Hill Evergreen Forest or event in some parts of the Tropical Rain Forest. In certain extremely dry sites, double burning in one season is common. These surface fires consume surface litter, other loose debris on the forest floor and small vegetation.

Table 1. Area burnt in each type of forests in 2000

Forest type

Area burnt

Hectare

%

1. Mixed Deciduous

63,420

68.0

2. Dry Dipterocarp

20,279

21.7

3. Secondary Growth

3,628

3.9

4. Forest Plantation

2,193

2.4

5. Hill Evergreen

1,858

2.0

6. Dry Evergreen

1,021

1.0

7. Bamboo

835

0.9

8. Natural Pine

90

0.1

Total

93,324

100

   Although other types of fire are not typical to the forest of these region, in recent years a notable number of crown fires took place in Pine Plantations. Also ground fires occurred in swamp forest. Such incidents of swamp forest fires are clear indication that climatic changes already have occurred in Thailand.

2.2 Duration

Forest fires in Thailand annually occur during the dry season from December to May with their peak in February-March. (Figure1)
 

Figure 1. Fire duration (data average from 1998-2003)

During the day, most fire activities concentrate from noon to 4 pm.


Figure 2. Fire frequency round the clock.

2.3 Fuel types and loads

    Since fires mainly taking place in seasonal forests, therefore it largely depend on dead fuel accumulated on forest floor during dry season especially dry litter and dead grass. However, undergrowth and dry twig also contribute to loads of fuel. Fuel load in Dry Dipterocarp is est. 4,000-5,000 kg/ha., while Mixed Deciduous contains 5,000 kg/ha. (Table 2)

 

Table 2. Fuel types and loads

Forest type

Site

(province)

Fuel loads (Kg/ha.)

Litter

Grass

Undergrowth

Twig

Total

Dry Dipterocarp

Chiangmai

1,980

1,480

1,070

660

5,190

 

Kanchanaburi

1,920

1,470

1,050

570

5,010

 

Petchaburi

1,645

1,230

889

548

4,312

 

Uthaitani

         
 

Sakonnakorn

-

-

-

-

4,133

Mixed Deciduous

Nakornrachasima

2,470

2,180

660

180

5,470

Grassland

Saraburi

-

-

-

-

11,170

Peatland*

Naratiwat

-

-

-

-

9,800

cu.m/ha

Table 3. Fire behaviors

Forest type

Site

(province)

Fire behaviors

Rate of spreads (m/m)

Flame length

(m.)

Fire intensity

(kw/m)

Dry Dipterocarp

Chiangmai

1.72

-

249.26

 

Kanchanaburi

2.81

-

-

 

Petchaburi

3.09

-

-

 

Uthaitani

 

0.7

110.71

Mixed Deciduous

Chiangmai

3.41

-

-

Grassland

Saraburi

8.29

5.7

2,165.8

2.4 Fire behaviors

    The common surface fires in Dry Dipterocarp as well as Mixed Deciduous Forests are quite moderate in intensities. Rate of fire spread approximately 2-4 metre/minute in fair condition. However rate of spread increases shapely upon the increase of slope. While in grasslands and dry-out bamboo forests, fires behave in a much more severe manner, flame length can reach 15-20 metres in steep slope or strong wind. Some data from experimental fires were shown in Table 3.

Table 3. Fire behaviors

Forest type

Site

(province)

Fire behaviors

Rate of spreads (m/m)

Flame length

(m.)

Fire intensity

(kw/m)

Dry Dipterocarp

Chiangmai

1.72

-

249.26

 

Kanchanaburi

2.81

-

-

 

Petchaburi

3.09

-

-

 

Uthaitani

 

0.7

110.71

Mixed Deciduous

Chiangmai

3.41

-

-

Grassland

Saraburi

8.29

5.7

2,165.8


 

 

[Type and Duration] [Causes][Annual burnt areas][Fire Impacts]