Fire in Dipterocarp Forests: 2. The Lowland Dipterocarp Rain Forest
2. The Lowland Dipterocarp Rain Forest
2.1 Impacts of Climatic Variability on Fire Regimes
2.2 Modern and Historic ENSO Events and Wildfires
2.3.1 First Damage Assessments
2.3.2 Natural Regeneration of the Dipterocarp Rain Forest of East Kalimantan after the Wildfires of 1982-83: Results of a Comprehensive Study
2.3.3 Rehabilitation of Burned Dipterocarp Rain Forests
2.1 Impacts of Climatic Variability on Fire Regimes
It is generally recognized that during the last Ice Age the transfer of water from the oceans to continental ice caps lowered the global sea level by at least 85 m (CLIMAP, 1976).
Besides exposing land, especially on the Sunda Shelf, the drop in ocean water levels may have caused the development of an overall arid climate at that time. In the highlands of Malesia, reliable palynological information and radiocarbon dating have clarified the climatic and vegetational history since the last glaciation, as well as the history of human impacts (FLENLEY, 1979b; MORLEY, 1982; MALONEY ,1985; FLENLEY, 1988; NEWSOME, 1988; NEWSOME and FLENLEY, 1988; FLENLEY, 1992). In his holistic appraisal of the geologic and biogeographic history of the equatorial rain forest, FLENLEY (1979a) suggests that compared to present conditions the most acute differences in the Quaternary climate of equatorial Indo-Malesia occurred during the period from ca. 18,000 to 15,000 before present [B.P.]. At that time, for example, the upper forest limit in the New Guinea highlands was 1700 m below its present level, while the mean temperature was 8-12° C lower.
Although palynological evidence from the tropical lowlands is still very scarce (FLENLEY, 1982), it must be assumed that lowland vegetation was generally that of areas with a more pronounced dry season. Lowland pollen analyses from West Malesia are, or appear to be, of the Holocene age (MALONEY, 1985), and no data from East Kalimantan are available.
However, the only study available from South Kalimantan may serve as an auxiliary argument for the climatic change which occurred during the Holocene. MORLEY (1981) suggests that the ombrogenous peat development of a peat swamp in the Sebangau River region had been initiated by a change from a more continental to a less seasonal climate during the mid-Holocene. This implies that the lowland climate of East Kalimantan, which today is still slightly seasonal (WHITMORE, 1984), must have been considerably drier within the period between the last glaciation and the development of today’s rain forest climate. At that time, fuel characteristics and flammability of the prevailing vegetation must have created conditions suitable for the occurrence of wildfires.
First evidence of ancient wildfires in East Kalimantan was found by GOLDAMMER and SEIBERT (1989, 1990). 14C-dates of soil charcoal recovered along an East-West transect between Sangkulirang at the Strait of Makassar, and about 75 km inland, showed that fires had occurred between ca. 17,510 and ca. 350 B.P. These events must have occurred in situ, as upper-slope hill terrain was selected for sampling in order to avoid dating of charcoal dislocated by sedimentation, deposits of which were found in the lower areas of Kutai National Park (SHIMOKAWA, 1988) and dated ca. 1040 B.P. (GOLDAMMER and SEIBERT, 1989). Charcoal residues suggesting ancient forest fires were also recently found in several places in Sabah (MARSH, pers. comm.) and Brunei (BECKER, pers.comm.).
The fire dates of 350 to 1280 B.P., as presented in the study, reveal that wildfires occurred not only during the dry Pleistocene, but also after the present wet, rain forest climate stabilized, at about 10,000 to 7000 B.P. These fires can be explained by periodic droughts such as those caused by the modern El Niño-Southern Oscillation [ENSO] complex.
The ENSO phenomenon, which has been comprehensively described (TROUP, 1965; JULIAN and CHERVIN, 1978; PHILANDER, 1983a; MACK, 1989), is regarded as one of the most striking examples of inter-annual climate variability on a global scale. It is caused by complicated atmospheric-oceanic coupling which is not yet entirely understood. The event is initiated by the Southern Oscillation, which is the variation of pressure difference between the Indonesian low and the South Pacific tropical high. During a low pressure gradient, the westward trade winds are weakened, resulting in the development of positive sea surface temperature anomalies along the coast of Peru and most of the tropical Pacific Ocean. The inter-tropical convergence zone and the South Pacific convergence zone then merge in the vicinity of the dateline, causing the Indonesian low to shift its position into that area. Subsequently, during a typical ENSO event, the higher pressure over Malesia leads to a decrease in rainfall. The severity of the dry spells depends on the amplitude and persistence of the climate oscillations.
In the rain forest biome these prolonged droughts drastically change the fuel complex and the flammability of the vegetation. Once the precipitation falls below 100 mm per month, and periods of two or more weeks without rain occur, the forest vegetation sheds its leaves progressively with increasing drought stress. In addition, the moisture content of the surface fuels is lowered, while the downed woody material and loosely packed leaf-litter layer contribute to the build-up and spread of surface fires. Aerial fuels such as desiccated climbers and lianas become fire ladders potentially resulting in crown fires or “torching” of single trees.
Peat swamp forests found in the lowlands of Borneo represent another fuel type. With increasing precipitation deficit and a lowering of the water table in the peat swamp biome, the organic layers progressively dry out. During the 1982-1983 ENSO, various observations in East Kalimantan confirmed a desiccation of more than 1 to 2 m (JOHNSON, 1984). While the spread of surface and ground fires in this type of organic terrain is not severe, deep burning of organic matter leads to toppling of trees and a complete removal of standing biomass. It is further assumed that smoldering organic fires may persist throughout the subsequent rainfall period, to be reactivated as an ignition source in the next dry spell (GOLDAMMER and SEIBERT, 1989). Such re-ignition is similar to fire behavior in organic terrain of northern boreal ecosystems.
The climatic variability during the past 18 millennia, with long-term changes and short-term oscillations, may give sufficient explanation for environmental prerequisites for wildfire occurrence. However, the origins of the fires are not clear and cannot be interpreted through the 14C-data of charcoal. Under the drier and more seasonal climate of the last glaciation, early anthropogenic fires and frequent lightning fires may have played a role similar to the conditions in today’s deciduous savanna forests of continental South Asia (see STOTT et al., 1990). Volcanism as another natural fire source may have influenced vegetation development on Southeast Asian islands with high volcanic activities, e.g., the highlands of Sumatra and Java.
Long-lasting fires in coal seams extending to, or near, the surface [Fig. 1], are found in various rain forest sites in East Kalimantan and are another important natural fire source (GOLDAMMER and SEIBERT, 1989; BIRD, 1995). It has been assumed that all of the ca. 150 coal seam fires known to be burning at present (WHITE, 1992) were ignited by the 1982-1983 wildfires. This is questioned by GOLDAMMER and SEIBERT (1989), since there are numerous oral reports of burning coal seams made before in 1982-1983 drought.
Fig.1. Subsurface coal seam fire under primary Dipterocarp forest near Muara Lembak, East Kalimantan (January 1989).
Fig.2. Surface fire orginated at a burning coal seam edge in Bukit Soeharto National Park during the drought of 1987 (September 1987).
GOLDAMMER and SEIBERT (1989) focused their research on dating ancient coal seam fires by investigating the “baking” effects of subsurface fires on sediment or soil layers on top of the coal seams. These effects of old, meanwhile exinguished, coal seam fires can still be seen today. The material, locally called “baked mudstone” is utilized at present for road construction purposes. Thermoluminescence analysis of burnt clay, collected on top of an extinguished coal seam in the vicinity of active coal fires, proved a fire event 13,200 to 15,300 years B.P. It is assumed that ancient coal fires were ignited by lightning.
The edges of the burning coal seams progress slowly through the ground of the rain forest and cannot be extinguished by water. Even a water body cascading over the edge of a burning coal seam cannot affect the combustion process, as observed by GOLDAMMER and SEIBERT (1989).
During the 1987 ENSO, the authors witnessed the ignition of a forest fire by a burning coal seam and its spread into the Bukit Soeharto forest reserve [Fig. 2].
These observations, together with the data on ancient fires and the longevity of coal fire occurrence, suggest that burning coal seams represent a permanent fire source from which wildfires spread whenever a drought occurs and fuel conditions are suitable for carrying a fire. This interaction between climatic variability, fire sources, and wildfires seems to be unique. However, further investigation of this phenomenon may well help to clarify the role and impact of long-return interval disturbances, like fire, in the evolutionary process of the rain forest biome.
2.2 Modern and Historic ENSO Events and Wildfires
The 1982-1983 drought in Malesia was the result of an extreme ENSO (PHILANDER, 1983b). In north and east Borneo, the decrease in rainfall began in July 1982 and lasted until April 1983, interrupted only by a short rainy period in December 1982. Monthly precipitation dropped below critical values along the coast and up to 200 km inland (see GOLDAMMER and SEIBERT, 1990; WALSH, 1995). In Samarinda, near the east coast of East Kalimantan, the rainfall between July 1982 und April 1983 was only 35% of the mean annual precipitation. Further inland, rainfall recordings from Kota Bangun [100 km from the coast] and Melak [150 km from the coast] still show critical deficits. The precipitation did not fall below the critical margin of 100 mm in Long Sungai Barang, Belungan [300 km inland]. These recordings support BRÜNIG’s (1969) observation from Sarawak, that drought stress occurs more frequently in coastal areas than in the hinterland.
Rainfall conditions in northern Borneo during the 1982-1983 drought were similar. Five stations in Sabah recorded an average precipitation decrease of 60% (WOODS, 1987, 1988). No significant drought and no fires were observed in Sarawak at that time (MARSH pers. comm.).
BERLAGE (1957) found that between 1830 and 1953, about 93% of all droughts in Indonesia occurred during an ENSO event. In systematic evaluation of precipitation data since 1940 (LEIGHTON, 1984), most of the 11 droughts recorded in 1941/42, 1951, 1957, 1961, 1963, 1969, 1972, 1976, 1979/80, 1982/83, and 1987 accompanied an ENSO. The worst droughts during that period were in 1941/1942, 1972, and 1982-1983, while the 1961 drought occurred independently of an ENSO event, and the 1965 ENSO did not cause drought in Indonesia.
The first documentation of the impact of an extreme drought in East Kalimantan is provided by BOCK (1881). This Danish zoologist travelled through the lowlands of the Kutai district of East Kalimantan 1878 and reported drought and famine which had occurred in the year before his visit. He noted that about one third of the tree population in the forests around Muara Kaman in the Middle Mahakam area died due to the drought. More recent observations in various peat swamp forests of the Middle Mahakam Area of East Kalimantan confirm that significant disturbances of this ecosystem must have occurred around 80-100 years ago (WEINLAND, 1983). The rainfall records of Jakarta [Java] 1877/78 explain these observations: between May 1877 and February 1878, rainfall in Jakarta was reduced by two thirds; a second severe precipitation deficit followed from July to December 1878 (KILADIS and DIAZ, 1986).
BOCK (1881) did not report any forest fires. Nevertheless, the authors looked for evidence of forest fires in East Kalimantan and were informed by AMANSYAH (pers. comm.) that his grandmother reported fires occurring in the area of Muara Lawa on the Kedang Pahu river during the period of investigation. Also GRABOWSKY (1890) mentions a forest fire on two mountains, Batu Sawar and Batu Puno, in the central part of South Kalimantan, about 70 km inland, which had occurred some years before his visit in 1881-1884. These two mountains, according to Grabowsky, had been totally deforested by the fire, and the approximate date of the fire coincides with Carl Bock’s remarks on the severe drought in East Kalimantan. Other sources and assessments of the 1877-78 drought are compiled by WALSH (1995).
In 1914-15, forest fires were again reported from Borneo. Published records were found for Sabah, where an area of 80,000 ha of rain forest and its superficial peat soil layer were destroyed by fire after an exceptionally dry period (COCKBURN, 1974). This area now forms the Sook plain grassland of Sabah. AMANSYAH (personal comm.) also reported fires, during the same period, in the Muara Lawa area. ENDERT (1927) confirms these reports in his reference to fires which had occurred about 10 years before his visit to East Kalimantan in 1925. According to the farmer RAJAB (personal comm.) of Modang [Pasir District of East Kalimantan] serious fires swept through his farmland from the coast, in the same year, before proceeding inland. Rainfall records from Balikpapan, and Samarinda close to the east coast of East Kalimantan, and from Long Iram, about 180 km inland, corrobate a severe drought in 1914-1915 (details in GOLDAMMER and SEIBERT, 1990).
Severe forest fires in Brunei following a drought of six weeks in 1958 were observed by BRÜNIG (1971). Smaller fires in lowland dipterocarp forests and in Dacrydium elatum forests were recorded for 1969 and 1970 in Sabah and Brunei by FOX (1976, cited by WOODS, 1987). BRÜNIG (1971) has also described an exceptional drought at this time, but no fires.
The meteorological information from Sandakan (Sabah) is of particular interest because of the availability of unusually long records: 1879-present, with two gaps in 1897-1901 and 1942-46 (WALSH, 1995). The data indicate two drought-prone epochs, between 1879 and 1915 and since 1968, with a drought-free period between 1916 and 1967. Long droughts of at least four months occurred five times in the period 1879-1915 [in 1885, 1903, 1905, 1906, 1915] and again on five occasions in the recent period 1968-92 [in 1969, 1983, 1986, 1987, 1992] (WALSH, 1995).
2.3.1 First Damage Assessments
The wildfire scene in Borneo in 1982/83 was set by the extreme drought and by numerous slash-and burn land-clearing activities which resulted in fires burning out of control. The extent and the immediately visible impact of these fires have been described by several authors and teams (WIRAWAN and HADIYONO, 1983; JOHNSON, 1984; LEIGHTON, 1984; LENNERTZ and PANZER, 1984; MALINGREAU et al., 1985; WOODS, 1987, 1989).
It is assumed that the overall land area of Borneo affected by fires exceeded 5×106 ha. In East Kalimantan alone, ca. 3.5×106 ha were affected by drought and fire. Of the total area, 0.8×106 ha was primary rain forest, 1.4×106 ha logged-over forest, 0.75×106 ha secondary forest [mainly in the vicinity of settlement areas], and 0.55×106 ha peat swamp biome (LENNERTZ and PANZER, 1984).
One of the first aerial and ground surveys of the fire damage was carried out in a burned area in the Kutai National Park, west of heavily logged and farmed areas (LEIGHTON, 1984). It was found that fire damage was higher in secondary forest than in primary forest, although the degree of damage varied greatly. The fires had swept twice through the ITO timber concession southwest of the Kutai National Park, the first causing defoliation of many trees and lianas; the second completely burning this accumulated litter. No surviving trees were observed in areas which had burned twice.
In his 1983 ground survey of the northern part of the National Park near the Meentoko research station, LEIGHTON (1984) found that the primary forest had been badly damaged. He was unable to report any unburned primary forest on hills, ridges, or slopes which could have served as a control plot to distinguish damage by drought or fire. He inferred that the drier soils of the hillside and hilltop areas, and also their shallowness (as argued by WITHMORE, 1984), could be an important factor determining the water deficit during prolonged drought seasons.
Narrow belts (width 5 to 20 m) of unburned primary forest flanking streams were also observed, but these account for only 5-10% of the total area. In the burned areas, 99% of the trees below 4 cm DBH had died, although about 10% were resprouting from the ground. Of the trees with 20-25 cm DBH, 50% had died and 20-35% of trees above 25 cm DBH. Among the larger trees which had died, only Bornean ironwood [Eusideroxylon zwageri T&B] was observed resprouting from the ground. Lianas and strangling figs had been virtually eliminated from burned parts of the forest, apparently being particularly sensitive to drought.
WIRAWAN (1983) made a ground survey in a less damaged area in the southern part of the National Park. Fire extended there about 30-40 km from the coast, but was able to sweep further inland wherever previous logging activities had produced suitable fuels, particularly in the surroundings of logging roads. The healthiest areas were in the southwest of the Park further inland. Dead stems of emergent trees sticking out of the canopy have apparently died from drought, not from fire. Canopy and subcanopy had regreened in these areas, while in burned forests, the subcanopy was usually defoliated due to heat rising from the fire.
WIRAWAN’s (1983) unpublished report shows that in unlogged, unburned dipterocarp forest the effect of the long drought period was more severe on larger trees than on smaller ones: 70% of the trees above 60 cm DBH were dead, while only 40% in the DBH class of 30 to 60 cm, and 20-25% in the class below 30 cm respectively. Drought has produced a diameter distribution similar to that in an unburned logged-over dipterocarp forest in that area.
Only 15% of trees in all diameter classes had died in unlogged, unburned ironwood forest. Dead individuals were mainly Shorea spp. and others, but ironwood was able to survive even on ridges. In unlogged, but burned ironwood forest, damage occurred particularly on smaller individuals: 75% of the trees below 5 cm DBH and 50% of the trees from 5 to 10 cm DBH were dead, compared with only 8-15% of the trees above 10 cm DBH. Many of the latter, however, sustained bark damage and may die in the near future.
Fire intensity in previously logged areas was directly related to the intensity of logging. The fires were severe but did not completely destroy moderately logged stands where, after the fire, a few trees with green foliage could still be observed, although spaced and scattered.
In heavily logged forest areas, where remaining trees ware widely spaced, shrub had formed a thick ground cover, providing an excellent biomass source for the fires after the extensive drought. Here the fuel consumption was more complete.
LENNERTZ and PANZER (1984) made several ground surveys in seven timber concessions throughout the burned area, confirming the findings of WIRAWAN (1983) and LEIGHTON (1984) on a larger-area scale. The damage was generally heavier in logged-over than in primary forests.
Fig.3. Primary rain forest along the road between Muara Wahau and Sangkulirang, East Kalimantan, affected by wildfire during the 1982-83 fire season (January 1989).
Fig.4. Regeneration of a burned primary forest near the road between Muara Wahau and Sangkulirang, East Kalimantan (January 1989). Pioneer species are recognized by large leaves, e.g. Macaranga spp.
Fig.5. Exploitation and repeated burning of Dipterocarp rain forest results in the formation of Imperata cylindrica savannas.
2.3.2 Natural Regeneration of the Dipterocarp Rain Forest of East Kalimantan after the Wildfires of 1982-83: Results of a Comprehensive Study
A series of studies on the regeneration of the fire-affected rain forest were conducted in the mid-1980’s and reviewed by GOLDAMMER and SEIBERT (1990). This synopsis included the investigations on a research plot established before the fire (RISWAN, 1976, 1982) and re-evaluated after the fire in 1983 and 1987 (SUYONO, 1984; BOER et al. 1988a,b; RISWAN and YUSUF, 1986), and the work conducted by BOER (1984), NOOR (1985), HATAMI (1987), BOER and MATIUS (1988), MYAGI et al. (1988) and TAGAWA et al. (1988).
In 1988-89 a comprehensive research project on the cause and effects of the forest fires of the 1982-83 fire season in East Kalimantan was carried out on behalf of the International Tropical Timber Organization [ITTO]. The study was conducted by the Forest Research Institute, Samarinda with technical assistance by Deutsche Gesellschaft für Technische Zusammenarbeit [GTZ]. On behalf of GTZ, the DFS Deutsche Forstinventur Service implemented the study.
The results of the study “Investigation of the Steps Needed to Rehabilitate the Areas of East Kalimantan Seriously Affected by Fire” were compiled in twelve individual reports. They deal with the cause and effects of the fire, give a damage assessment and provide proposals for the rehabilitation of the burned areas (summary in SCHINDELE, 1989; detailed bibliographical data of the reports are given at the end of the list of references). Also steps for future fire prevention are suggested. An important and very valuable result of the study are the vegetation classification and the forest rehabilitation maps at a scale of 1:250.000. The most important results are summarized below.
Study area
Study area was the Mahakam basin which was most seriously affected by drought and forest fires. The mapped study area has a total size of 4.7×106 ha and stretches from the east coast of Borneo to the mountainous areas in the centre and in the north. The southern boundary is formed by a line from Balikpapan to Long Iram.
Methodology of the study
In the study area a two-phase forest inventory was implemented. During the first phase the vegetation of the study area was stratified with the help of satellite imagery:
- SPOT XS multispectral imagery, resolution 20×20 m [1987/88]
- SPOT panchromatic imagery, resolution 10×10 m [1989]
- Landsat MSS, resolution 80×80 m [1983-84 and 1987].
Areas not covered by satellite scenes or where scenes were obstructed by clouds were investigated with the help of video remote sensing.
Within the second phase, a forest inventory was conducted in the field. The inventory design applied was a double cluster system of triangular shape. The individual clusters were distributed randomely within the different strata. Besides the data on vegetation, for every individual sample plot additional information on site [soil, topography] and other parameters [forest condition prior to fire, fire intensity, year of logging, etc.] was collected. Altogether 96 clusters were placed throughout the study areas, and a total of 1663 individual sample plots were inventoried.
Results
Cause and extent of the fire
Within the study area the actual area affected by fire was ca. 3.2×106 ha of which 2.7×106 ha were tropical rainforests. Table 1 shows the distribution of the different vegetation classes based on satellite imagery analysis. The area was classified according to fire damage classes [Tab.2]. The interpretation of the inventory data revealed the following results:
Tab.1. Distribution of vegetation classes
Vegetation Classification Area in
(x1000 ha)
(%) Burned
(%) Unburned
(%) Undisturbed Forests 410 9 11 89 Lightly Disturbed Forests 1096 23 58 42 Moderately Disturbed Forests 984 21 84 16 Heavily Disturbed Forests 727 15 88 12 Plantations 1) 27 1 96 4 Total Lowland Forests 3244 69 67 33 Kerangas Forest 40 1 45 55 Limestone Hills & Rocks 43 1 56 44 Undisturbed Swamp Forests 181 4 17 83 Disturbed Swamp Forests 385 8 97 3 Open Swamps (Brush etc.) 110 2 82 18 Brackish Swamp 22 0 23 77 Tidal Forests 41 1 0 100 Total Forest Vegetation 4066 86 67 33 Shifting Cultivation 2) 387 8 85 15 Perm. Cultivated Areas, Settlements 213 5 69 31 Lakes and Rivers 67 1 0 100 Total Other Land-use 667 14 79 3) 21 Total Mapped Area 4733 100 67 33
1) That means 96% of the area which were plantations in 1988 (SPOT) were burned areas in 1983; it does not mean that 96% of plantations were burned
2) For shifting cultivation same as 1)
3) Excluding water surface
Tab.2. Definition of fire intensity classes
Fire intensity Criteria 0 No fire No signs of damage 1 Low Sights of damage only in understory 2 Moderate Part of overstory damaged 3 High Overstory completely burned
Forests on sites with low water retention capacity were most seriously affected by fire. This refers especially to peat swamp forests, heath forests [Kerangas], forests on limestone hills and rocks [Tab.1] and all other forests on shallow soils [Tab.3].
On the other hand, logged-over forests were particularly affected by fire [Tab.4], especially those growing on drought-sensitive sites. There is a close correlation between the year of logging and fire intensity [Tab.5]. Especially forests which had been logged shortly before the fire event were very seriously damaged. Finally, forests in the vicinity of settlements and along rivers and roads were particularly affected by the fire [Fig.3].
Tab.3. Fire intensity and soil depth in number of sample plots and in percent of each soil depth category
Fire intensity Depth of soil in cm 0-14 15-29 30-59 60-99 >99 No fire 2 (3%) 7 (13%) 14 (5%) 44 (4%) 69 (27%) Low 20 (29%) 5 (10%) 86 (31%) 221 (22%) 53 (21%) Moderate 18 (27%) 17 (32%) 66 (23%) 347 (34%) 76 (30%) High 28 (41%) 24 (45%) 113 (41%) 398 (40%) 55 (22%) Total 68 (100%) 53 (100%) 279 (100%) 1010 (100%) 253 (100%)
Corrected continguence coefficient is 0.36
Chi2 positive on 0.1% level
Tab.4. Forest condition prior to fire and fire intensity
Fire intensity Forest condition prior to fire Primary logged – over N % N % No fire 83 5 (18) 53 3 ( 4) Low 127 8 (27) 258 16 (22) Moderate 110 7 (24) 414 25 (34) High 141 8 (31) 477 28 (40) Total 461 28 (100) 1202 72 (100)
Corrected continguence coefficient is 0.39
Chi2 positive on 0.1% level
The number in brackets is the percentage of plots within one forest type
Tab.5. Year of logging and fire intensity
Fire intensity Year of logging <74 74-75 76-77 80-81 82-83 >83 No fire 71 0 1 0 2 36 Low 120 27 55 27 34 51 Moderate 126 50 78 87 40 56 High 172 43 113 114 14 57 Total 489 120 247 228 90 200
Corrected continguence coefficient is 0.35
Chi2 positive on 0.1% level
Effects of the fire
The analysis of the inventory results for different tree species allowed the following classification according to their sensitivity to fire:
Species promoted by fire
Euphorbiaceae are definitely the family mainly promoted by fire in a linear relation; the higher the fire intensity, the higher was their importance value compared to the other families. Particularly Macaranga triloba and Macaranga gigantea were promoted. Macaranga spp. and other Euphorbiaceae are, in general, very light demanding and fast growing [Fig.4]. A diameter increment of 2 cmxyr-1 is quite common. Most of the Euphorbiaceae belong to the pioneer species. Other species promoted by fire are Moraceae [Ficus spp.], Datiscaceae [Octomeles spp.], Leeaceae [Leea indica], Rubiaceae [Anthocephalus spp. and Nauclea spp.], Sonneratiaceae, Ulmaceae [Trema spp.] and Verbenaceae [Vitex spp.].
Fire resistant species
Species were classified as fire resistant when they appeared in the different strata independent of fire intensity. The following genera and species belong to this category: Lauraceae [e.g., Eusideroxylon zwageri], Caesalpinaceae, Ebenaceae [Diospyros spp.] and Palmae. The natural regeneration of these species, however, is not favoured by fire.
Species suppressed by fire
The most important family in East Kalimantan, the Dipterocarpaceae is clearly suppressed by fire due to thin bark, high content of flammable resin, and lacking resprouting capability. However, in lightly disturbed forests where seed trees survived, natural regeneration of Dipterocarps was observed. Other genera supressed by fire are Anarcardiaceae, Annonaceae, Burseracea, Fagaceae, Melastomaceae, Meeliaceae, Myristicaceae, Myrtaceae, Sapindinaceae and Sapotaceae.
Table 6 depicts the 10 most important families according to their rank (based on the abundance) on sites affected by various fire intensities. Surviving trees were damaged by fire to various degrees, especially the Dipterocarps. Tree vitality [percentage of crown still in leaf; Tab.7] was considerable reduced, and about 40% of the stems of the surviving Dipterocarps were injured [Tab.8].
It is concluded that biodiversity of fire-affected forests is considerably reduced with increasing fire intensity. Pioneer species, particularly the Euphorbiaceae, are promoted by fire.
Tab.6. Ranking of tree families within fire intensity classes, based on abundance.
Fire intensity 0 1 2 3 Dipterocarpaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Dipterocarpaceae Verbenaceae Verbenaceae Myrtaceae Lauraceae Lauraceae Moraceae Anacardiaceae Myrtaceae Dipterocarpaceae Mytraceae Sapotaceae Sapotaceae Moraceae Lauraceae Lauraceae Moraceae Leeaceae Leeaceae Caesalpiniacaea Ebenaceae Datiscaceae Dipterocarpaceae Myristicaceae Verbenaceae Myrtaceae Rubiaceae Moraceae Anarcardiaceae Rubiaceae Datiscaceae Annonaceae Sonneratiaceae Sonneratiaceae Ulmaceae
Tab.7. Definition of vitality classes
Vitality class % of crown in leaf 0 80 to 100 1 50 to 79 2 20 to 49 3 1 to 19 4 dead
Tab.8. Crown vitality and decay according to fire intensity.
Tree family Fire Intensity 0 1 2 3 0 1 2 3 Vitality classes Decay % Anacardiaceae 0,6 0,8 1,7 1,6 5 14 20 15 Caesalpiniaceae 0,8 0,9 1,4 1,9 0 8 30 54 Dipterocarpeaceae 0,9 1,0 1,6 1,9 11 10 25 40 Lauraceae 0,7 0,8 1,3 1,5 2 13 21 27 Moraceae 0,5 0,9 2,1 1,9 0 21 22 10 Myrtaceae 0,7 0,9 2,4 1,9 0 18 37 58 Rubiaceae 0,9 0,9 1,7 0,8 17 0 8 2 Saptoaceae 0,9 1,3 1,7 1,2 10 14 21 50
2.3.3 Rehabilitation of Burned Dipterocarp Rain Forests
As a follow-up to the inventory of fire damages in East Kalimantan, a subsequent project “Establishment of a Demonstration Plot for Rehabilitation of Forest Affected by Fire in East Kalimantan” was initiated in 1992 by the Ministry of Forestry in Indonesia with the financial support of ITTO [Forest Research Institute Samarinda, 1994]. On the demonstration plot [total size: 1.099 ha] various rehabilitation techniques were performed, e.g., reforestation with local fast growing species and Dipterocarps, enrichment line planting with Dipterocarps, enrichment planting under open pioneer species canopy, and selective tending. This project is still being evaluated. Applied research is attempting to consolidate and improve the rehabilitation methods.
Top
Back
