Forest Fire and biotic interferences (IFFN No. 26)

Forest Fire and Biotic Interferences-A Great Threat to Nilgiri Biosphere

(IFFN No. 26 – January 2002, p. 32-36)


India constitutes one of the mega biodiversity countries of the world, which is abundant with unique and diversified floral and faunal wealth. Western Ghats of peninsular India, a green lung between bay of Bengal and Arabian sea plays a vital role regarding biodiversity in southern India. The prevailing tropical climate coupled with physical and biotic factors have unitedly made an impact on resources of many ecosystems, which are highly complex and fragile in nature. The land ecosystem is facing mounting problems in the hands of man. Biotic pressure due to increasing populations periodically covers larger areas in the tropical forests of southern India destroying timber and other properties.

Nilgiri Biosphere Reserve (NBR) in western ghats is a major floristic region of southern India. Biotic influence in this area is very heavy. The natural vegetation of the higher elevation of the Nilgiri plateau comprises of patches of sholas (montane broad-leaved evergreen forest) and grassland (scrub-savannah). The montane forests are generally confined to the sheltered sites such as valleys, hollows and depressions where moisture is higher. The grassland comprises of grasses, herbs and shrubs in varying proportions. Since population explosion, heavy biotic pressure existing continuous in these forests and grassland. Present paper deals with land use change and other human interference in these forests.

Nilgiri Biosphere Reserve

The NBR is most important floristic region embraces the sanctuary complex of Wayanad, Nagerhole, Bandipur and Mudumalai. It has a total area of 5520 km2 with core area of 1240 km2 and buffer zone of 4280 km2. This area is lies in Western Ghats of peninsular India. It was declared the first biosphere reserve of India on 1 September 1986. It has a unique bio-geographic region with many endemic floral and faunal species covering three states i.e. Tamil Nadu, Kerala and Karanataka. Entire area is having countless micro flora, fauna and the germplasm bank of various rare, threatened and endemic species and are facing continuous pressure by one way or the other. The average annual rainfall of this reserve ranges from 500 to 7000 mm.

Table 1. Percentage of protected area, reserve forests and core area of the NBR in the three states

State Protected Area Reserve Forests Core Area
  Sq. Km % Sq. Km % Sq. Km %
Karnataka 1513.56 64.48 462.70 14.49 701.80 56.58
Kerala 433.92 18.49 858.80 26.90 264.50 21.32
Tamil Nadu 399.56 17.03 1870.66 58.60 274.00 22.09


Belonging to the Indo-Malayan realm, its biodiversity ranges from tropical dry deciduous forests to tropical rain forests. The NBR has more area uner reserve forests (59%) than the protected area in Tamil Nadu (Table1). Although these forests are being subjected to severe biotic pressures, it has good population of Elephant (Elephas maximus), Gaur (Bos gaurus), Sambhar (Cervus univolor), Nilgiri Langur, Nilgiri Tahr, Four Horned Antelope, Blackbuck, hyena (Hyaena hyaena), Tiger, Leopard and Wild Dogs. The main reason for large-scale biodiversity is due to the fact that it is having conducive climatic conditions. The average high annual rainfall and the variation in temperature also reflects in a vast range in different types of forests from dry deciduous to montane evergreen forests. However, the most distinct feature is the development of the tropical wet evergreen forests, more prominent along the windward side of the humid tropical belt of the southern region. These forests are characterized by multistoried structure with emergent species raising their crowns above the general canopy layer, and as a result imparting undulating look to the canopy surface. The tallest emergent trees may grow up to 60m with slender and clear boles and often buttressed at base. The light coloured bark in a number of tree species is less than 3 mm thick. The copious growth of feeder roots in the soil surface occupying the interface of the decaying litter layer and mineral matrix of the soil is yet another characteristic of these forests. The biodiversity spread over wide ranges of hills of Nilgiris, Neelambur and Siruvani hills from where numerous rivers rolls down to the below viz. Bhawani, Siruwani, Cauvery and Shailkudri etc.

A characteristic feature of this biosphere is the occurrence of shoals (montane forests) above 1500 m. They are found in patches in hollows and sheltered folds surrounded by rolling downs in the Anamalais, Nilgiri and Palni hills and the high ranges of Kerala and Karnataka. Montane evergreen forests have thick undergrowth; the trees are short boled and attain a low height of 15-20m. That the shoal forest community had wider distribution in the past has been established through pollen analytical investigations. The rich soil exposed after the clearance of forest, erodes rapidly under the prevalent climatic conditions and the operating biotic factors and the absence of suitable edaphic conditions prevent the regeneration of these forests. This non-regenerating, and fast receding shoal forest is a dying community; more appropriately called a ‘living fossil community’ (Vishnu-Mittre and Gupta 1968). Meher-Homji (1965) opines that two adverse factors, viz. frost during the cold season, and fire during the drier months, prevent the spread of the shoals.

Cattle Pressure

The loss of grasslands has another severe impact on the existing forests. Traditionally the Todas used the grasslands to graze their buffaloes and probably the first cattle in this area did the same. But with the increasing cattle number and decreasing grasslands the only place left where the cattle could be fed was the shoals and they were made full pressure on sholas. Moreover, the grasses dry out in the winter and is unpalatable, so this is another reason for the use of shoals by the cattle and especially in this period the sholas seem to be totally relied upon. People prefer to be surrounded with cultivated plants and farms along with more and more number of animals, which resulted heavy damages to sholas and grassland (Chitrapu 1986).

Over-grazing has been identified as a factor responsible for the degradation of the forests ad the resultant increase in the number of weeds. The spread of such weeds has taken away much of the fodder resources as such obnoxious weeds cannot be grazed upon. Measures to contain such factors, albeit minor, have been suggested by Gadgil (1984).

Fire Hazards

The greatest pressure on forest is by way of forest fire. The man for his own greed is putting fire every year in one or the other part of Nilgiri biosphere causing more than 1000 ha annually heavily intentional fire which is not only retarding the growth of existing standing vegetation but also not allowing new recruits to emerge out on the forest floor (Srivastava 1997). In the process of which many endemic species are disappearing from their native place. The exotics which were introduced long back such as wattle, Eucalyptus, Eupatorium, Cestrum, Eulex species in the Nilgiri plateau having strong germination percentage and invading very fast in fire burnt areas. The ill effects of this are too well known and too numerous to be enumerated. Spread of alien weeds can be destructive to native species. More importantly, species like Lantana camara var aculeata and recently Eupatorium odaratum, Mikania cordata, Parthenium hysterophorus, Eulex europeaus, Cestrum nigrum. Cassia tora etc have invaded the NBR and tend to smother the natural vegetation. The wattle, introduced long back, has now become a weed.

Intentional setting fire to the seasonally dry forests has disastrous effect so much so that such forests may not resume the original shape at all. In addition to slash-and-burn cultivation practiced almost throughout the NBR also causing ill effects to the vegetation.

Ascending growth of human and cattle population accelerate the forest fires which play a predominant role in the process of devastation of large areas. The local cattle grazers often set ablaze grazing areas in the hope of getting new shoots. The head loaders destroy vegetation to create pathway through the forests. The encroachers set fire to forest in order to clear the land for agricultural purpose. The careless tourists throwing away lighted matches and cigarette butts start fire, which not only reduce the trees and herbs to ashes but also damage of wildlife.

Forest fires and indiscriminate grazing are the most important factors that affect the natural regeneration in the forest and cause its degradation. These results further reveal that moist deciduous forest have more incidences of fire while dry deciduous and thorny forests are more subjected to grazing. After going through the records and observation made, it is found that major cause for the depletion and loss of bio-diversity in the Nilgiris is man made fire. The recurrent fire set by grazers during summer (in southern India the summer starts from January onwards), has dealt a severe blow to the floristic composition. Forest fires either natural or man-made play a significant role in ecosystem dynamics. In the Nilgiris up to an extent Todas have played the role to convert the sholas into grassland. On the other hand in the North Coimbatore plateau for instance where the forest is burnt regularly and the incidence of grazing for heavier than that of Toda grazing on the Nilgiris. Moreover, the average rainfall is considerably less, the forest has become undoubtedly degraded and open, but shows no signs of disappearing. Grassland occur at similar elevation on the Palnis and the Anamalais where no Todas live (Ranganathan 1941). Here it has to be reiterated that the grasslands are an integral part of the natural vegetation of the Nilgirs. Paleo-ecological studies of the vegetation show the presence of extensive grassland at least 20000 years ago (Sukumar 1993), showing that they are also a climatic climax of the area. Recurrent fire decreases the green cover through prevention of regeneration and leads to the slow death of the forest. It also increases erosion and alters the physical and chemical properties of the soil, converting organic ground cover to soluble ash and modifying the microclimate through the removal of overhead foliage. The soluble ash is washed away in the next rain. Fires can also make trees more susceptible to insect attack. Simultaneously much woody vegetation present in the grasslands disappears. The upper most layer of soil, which is in the process of formation of humus, gets very badly affected and microbial organisms that play a very vital role in the system get destroyed. Severe burns such as those caused by wildfire can result in nearly complete destruction of organic matter and bring about changes in the physical, chemical and biological properties of the upper layers of mineral soil.

Forest fires ceases their effects on climate change vigorously. In the past decade researcher have realized the important contribution of biomass burning and it is recognized as a significant global source of emission contributing as much as 40% of gross Carbon dioxide and 30% of tropospheric ozone (Andreae 1991). Heavy smoke during forest fires also damage the forest ecosystem. In a study in Garhwal Himalaya forested area under smoke plumes has been estimated as 130.96 km2 or 2.96% of total forests area (Roy 2000).

Changing Landscape

The biodiversity of NBR started getting deteriorated from 1832 onwards with the impact of human population and entry of exotics. There was maximum 92.3 % decrease in area under shola forest was recorded in the catchment area of Ooty from 1949 to 1992 and during the same period maximum 100 % decrease in the area under grassland was recorded in catchment areas Deva shola, Parson`s Valley and Ooty, respectively (Table 2). Not only the original habitat has sunk but also faces continuous pressure in one way or the other with the increase in population, which started with a few in 1840 to the tune of lakhs at present. Most of the human population visits this habitat for their basic needs and survival. Some of them visit this area primarily for fuel wood collection, some of them for grazing livestock and few for collecting Minor Forest Produce. The fuel wood is mostly collected from the hill slopes.

It is also worth mentioning that there is an overlap in the habitat use by man and wildlife. Elephant, Spotted deer and Sambar prefer many of the plant species, which are collected by the villagers as fuel wood. Similarly human interference has caused poor density in respect of Emblica officinalis in the process of collection of Emblica fruits. Continuous lopping of trees results in loss of population of Emblica. Indirectly it deprives herbivores i.e. Spotted deer/Sambar of their food. Thus a very strong destructive factor which has vital role in degrading forest in these ghats is man, who has been continuously interfering with natural vegetation, clearing and burning it, grazing his innumerable cattle removing forest produce at will, killing wildlife and carrying on shifting cultivation and raising various plantations. These activities have resulted in serious erosion, drying up of rivers and recurring droughts and fragmenting forested areas. Head loaders, cattle grazers, MFP collector’s etc, in general people are unaware of the bio-diversity concept sensing the shortage of fuel wood, the foresight of the forester had led to planting of Eucalyptus and Wattle in order to protect these living fossil forests. But increasing demand from the public and industries did not spare the shoals by late 20th century. Cattle population has also increased manifold in the upper hills, trampling the indigenous flora and disturbing the eco system. Apart from this poaching of endangered species has also led to shrinkage of wildlife. Hundred years back the anthropogenic pressure was not much on the Nilgiri hills and the forest green cover was much more compared to what it is now. Ultimately the original landscape of both these beautiful hills has changed.

The Nilgiri plateau has undergone vast changes through the past century. The scene in the past was strikingly different from what it is today. Ouchterlony’s map served as an important document to show us the scenario of a century and a half ago and also proved useful for a comparative study of the land use patters. (Saravana 1993). There has been a noticeable decrease in the natural vegetation cover over this period. It refers to both the shoals and the grasslands because most people prefer to call the shoals as forested lands while they consider the grasslands as wastelands. The shoals have reduced by half (from almost 8600 ha to about 4225 ha), the grasslands have come down by factor of six (from 29875 ha in 1849 to about 4700 ha) (Table 3). With increase in population and influx of settlers especially when the various hydel projects were under construction, there was an increased need for more land, housing and cultivation purposes. Also the Nilgiris had a climate well suited for tea cultivation. In a long span of time of 143 years almost 26000 ha of grasslands have been replaced by cultivation (12,400 ha), tea (11,500 ha), wattle (9775 ha) and Eucalyptus plantations (5150 ha).

Table 2. Past and present area of the shoals and grasslands in different catchments (Kumar 1993)

Catchment Area under shoal in ha Area under grassland in ha
  1849 1992 Decrease% 1849 1992 Decrease%
Emarald 550 450 13.9 2025 375 80.3
Avalanche 300 850 1450 625
Upper Bhavani 275 1300
Sillahalla 725 150 78.3 3075 25
Kundah 725 625 16.5 1200 150 87.9
Deva shola 900 125 0 3800 0 100
Kothibenu 775 150 100 2425 75 92.7
Keti-Kateri 100 0 69.9 1450 100 95.3
Porthimund 200 175 16.6 625 300 53.8
Mukurthi 1050 125 87.8 1250 600 57.5
Pykara 1000 350 60.9 3550 125 96.1
Kamarajasagar 375 100 72.9 2800 75 97.3
Parson’s Valley 375 170 53.5 950 0 100
Ooty 325 25 92.3 675 0 100
Naduvattam 750 125 81.4 1175 375 64.4
Pykara River 300 75 77.4 900 100 89.9
Sholur Kokul 200 150 24.8 775 50 94
Sandynala 750 125 83.4 2950 550 81
Anikorai 400 50 87.5 1925 25 98.8


 Table 3. Changing landscape pattern of Nilgiri Biosphere Reserve (Kumar 1993)

Total Area

Ouchterlony’s Map (1849) Current Map (1992)
Sholas 8,600 ha 4,225 ha
Grasslands 29,875 ha 4,700 ha
Cultivation 10,875 ha 12,400 ha
Tea 0 ha 11,475 ha
Wattle 0 ha 9,775 ha
Eucalyptus 0 ha 5,150 ha

These figures are only for those area covered on the map while there is some additional area left on the eastern edge. The only region that seems to have been spared is a few pockets within the Mukurthi National Park. This too was not really left alone but plateau with wattle, which failed to survive and the grasslands seem to be coming up again.


The Nilgiri biosphere, which is having countless micro flora, fauna and the germplasm bank of various rare, threatened and endemic species are facing continuous pressure by one way or the other. The greatest pressure on forest is by way of forest fire. The man for his own greed is putting fire every year in one or the other part of Nilgiri biosphere causing more than 1000 ha annually under fire which is not only retarding the growth of existing standing vegetation but also not allowing new recruits to emerge out on the forest floor. In the process of which many endemic species are disappearing from their native place and giving mosaic pattern to the landscape. If the process is not being checked many of the endemic flora and fauna will disappear from the biosphere reserve even before its documentation is completed. The exotic which were introduced long back such as Acacia meansii,, Eucalyptus spp, Eupatorium grandilosum, Cestrum nigrum, Eulex europiaus etc. in the Nilgiri plateau if not checked will slowly take over the place of native. Monoculture plantation of tea, coffee and other forestry species have already change the landscape. It is the right time for the foresters, naturalists and environmentalists to concentrate and solve this problem by way of utilizing some of these exotics as a fire wood for the neighbouring rural masses and regular women head loaders. It also reminds us to protect the beautiful creature from the indiscriminate destruction. Forest fire is one of the major detrimental factors in depletion of biodiversity of Nilgiri biosphere. If not checked at this juncture it will not only lead to reduction in forest covers but also pave way to unfriendly species to ecosystem by wiping out the sensitive endemic species forever. The people along the reserve forests are not very clear about the biodiversity conservation concept. The role of each organism in an Eco system is largely unnoticed. At this juncture the awareness alone can bring down the incidences of destruction. It is the foremost duty of every human being to come forward for repairing the loss already done to our nature treasure.

IFFN/GFMC contribution submitted by:

Rajiv K. Srivastava
Assistant Director General

Indian Council of Forestry Research and Education

Dehra Dun 248006

 Tel:            ++91-0135-757485
e-mail:       srivastavark <>


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Country Notes
IFFN No. 26

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