- Using satellite data, researchers quantified fires across Nilgiri Biosphere Reserve, located in the Western Ghats, from 1973 to 2014. The results showed that overall fires have been decreasing in both the size of the burnt area and frequency from 1989 to 2014, indicating management effectiveness in suppressing fires.
- Fire frequency maps generated from this study can be used to develop conservation strategies and calculate carbon emissions.
- An expert warns that excessive fire suppression may result in the build-up of fuel leading to more intense fires in the future.
Since the development of the Nilgiri Biosphere Reserve in the Western Ghats in 1986 — the first such reserve to have been established in India — active measures have been taken to suppress forest fires, most of which are caused by humans and can affect biodiversity in the region. But the biosphere managers need to evaluate the effectiveness of the past fire suppression measures to plan future courses of action.
A new satellite-based study by a team of researchers from ISRO’s National Remote Sensing Centre in Hyderabad and Andhra University has now quantified fires in the entire Nilgiri Biosphere Reserve over the past 40 years, revealing that fires in the reserve have declined in both area and frequency. Previous studies so far have looked at the status of fires in the reserve, but most were focused on a small area within the reserve or considered a short time period in their analysis.
The researchers attributed this decline to effective fire management strategies implemented after the reserve was established. Annual fire management plans had been carried out in the reserve, which involved local communities through Joint Forest Management committees by the Forests and Wildlife Department and non-governmental organisations (NGOs).Using data from both NASA’s Landsat satellites and Indian remote sensing satellites, the researchers of the study mapped out the area of forest burnt and analysed the spatial patterns and frequencies of fires in the reserve from 1973 to 2014 — a period of four decades. Nilgiri Biosphere Reserve encompasses six protected areas among which four are national parks and two are wildlife sanctuaries.
The team analysed the distribution of the burnt area across different types of vegetation, protected areas and management zones within the reserve. In addition, they determined the effect of temperature, elevation and accessibility to roads on the extent of the fires.
Declining trends in the burnt area
The study revealed that overall fire incidences have been declining from 1989 to 2014 in the reserve. The burnt area, mostly due to ground surface fires, was highest in 1989 standing at 1318 square kilometres (sq km) and lowest in 2013 at 15.7 sq km. Although fires have gradually declined in the recent decade from 2005 to 2014, there was a spike in the area burnt in 2007 (367.4 sq km).
Most of the burnt area consisted of dry deciduous forests, moist deciduous forests, savannah, scrub and grasslands. This was expected as dry deciduous forests and scrub, have plenty of “dry combustible material in the form of grass and leaf litter,” stated the researchers.
All protected areas showed a declining trend in the burnt area from 1989 to 2014, which the researchers attributed to effective management practices. Notably, fire incidents affecting dry forests were highest in Bandipur National Park, followed by Mudumalai Wildlife Sanctuary, and Nagarhole National Park. Bandipur National Park had the highest burnt area recorded in 1989 (343.5 sq km) and the lowest area in 2013 (3.8 sq km).
The researchers explained that the dry and moist deciduous forests usually shed their leaves by the end of January, leaving a high load of fuel. During the summer heat, the fuel loads become dry and combustible.
Fire frequencies and the size of burnt patches across the reserve have also decreased during the study period. Dividing the area of the reserve into 7,111 grids, each covering an area of 1 sq km, they found that among the grids with natural vegetation (6,489), two-thirds were affected by fires. Of these, two-thirds of the grids had a low fire frequency (between 1 to 5 times). Also, the area covered by large burnt patches (5 sq km) as well as smaller patches had dropped over the study period and the density of fires had decreased in the recent decade, from 2005 to 2014.
The team suggests that the gradual decline in forest fires from 1989 to 2014, points to the effectiveness of protected areas within the reserve in managing forest fires.
For management purposes, the reserve is divided into four zones: core, manipulation (forestry), manipulation (tourism) and restoration. Both manipulation zones (forestry and tourism) form the outer part of the reserve and prescribed burning in the latter is performed sometimes to reduce the fuel loads. The researchers noted that the manipulation (tourism) and the core zones of Bandipur and Nagarhole National Parks had more fires. But overall, fire incidences in all of the zones declined from 1989 to 2014.
By analysing the frequency and locations of past fires in the reserve, the team also modeled hotspots of high fire risk. In terms of vegetation type, most of the fire hotspot areas were comprised of dry deciduous forest (40 percent), followed by moist deciduous forest (22.3 percent) and scrub (9 percent). Among the protected areas, the buffer zone of Silent Valley emerged as a hotspot with a high frequency of fire locations followed by Bandipur National Park, Nagarhole National Park and Mudumalai Wildlife Sanctuary.
Climate factors and proximity to roads affect the burnt area
As the researchers expected, the study showed that the burnt area was greater at lower elevations with higher temperatures and decreased when progressing to higher elevations with lower temperatures. K.V. Satish, co-author of the study, who was a research fellow at the National Remote Sensing Centre during the study, explained that the “lower elevation regions of Nilgiri Biosphere Reserve are covered by deciduous forests and these forests usually shed their leaves by the end of January and therefore produce high fuel loads.”
Another anticipated finding was that the burnt area was larger when closer (within 100m) to roads in the buffer zones than in areas farther away (500m) from roads. Buffer zones of the reserve and protected areas are often managed through prescribed fires.
According to the team, the fire frequency maps generated from this study can be used to develop conservation strategies, study forest regeneration and calculate carbon emissions.
“This study certainly provides comprehensive statistics and geographical extent of forest fires in the Nilgiri Biosphere Reserve derived from satellite data,” said Raman Sukumar, a professor at the Indian Institute of Science, Bengaluru, who had played a role in designing the reserve. “In spite of certain limitations in relying solely on satellite data, this is the best way to map fires across such a large geographical scale.”
Sukumar published a study in 2013 on how weather patterns affected fire incidences in Mudumalai Wildlife Sanctuary from 2004 to 2010. His team noted that fires had reduced in the later years than they had expected from the environmental relationships and that this may be because of active management in suppressing fires.
He pointed out that fires may follow complex cycles related to the prevailing climate and management regimes. As a result, “taking a base year from the decade of the 1980s for deriving trends may be misleading because this was a period of two major El Nino events,” which, he explains, drive extreme aridity and are likely responsible for the peaks in fire activity during the 1980s. “Since then,” he noted, “the incidences of fire have reduced, given the relatively normal or excess rainfall.”
But, “even if fire frequencies have reduced,” cautioned Sukumar, “fire intensities may not have.” He added: “We must remember that excessive fire suppression leads to build up of fuel for more intense fires later.”
Reddy, C.S., Satish, K.V., Rao, P.P.V.V. (2018). Significant decline of forest fires in Nilgiri Biosphere Reserve, India. Remote Sensing Applications: Society and Environment, 11, 172-185. doi.org/10.1016/j.rsase.2018.07.002
Banner image: A village inside the dense forest of the Nilgiri Biosphere Reserve. A study has shown a decline in forest fires in the NBR owing to effective fire management strategies implemented after the reserve was established. Photo by Anoop K/Wikimedia Commons.