MSc

Fire is being used as a tool in forest management and protection in several
parts of the world. A forest fire is an unplanned, uncontrolled and unpredictable
fire in an area of combustible vegetation. The after effects of forest fire includes
air pollution, destruction of forests and wildlife, altered species composition,
outbreaks of pests and diseases etc. The frequency of wild fires around the world
increases with changing climate. Considering the growing importance of tropical
forest ecosystems and also because of its fire susceptibility, it is relevant to study
the effects of forest fire on vegetation and soil in a forest ecosystem.
The present study was undertaken in Chembikkunnu area of Poongode
section of Wadakkanchery forest range in Thrissur forest division in state of Kerala.
The study was carried out to assess the impacts of an unplanned forest fire on the
vegetation and soil physico-chemical and biological properties in the fire burnt
areas of Poongode section of Wadakkanchery forest range of Thrissur forest
division. Concurrently the study also compared and contrasted the changes in
vegetation and soil between burnt and control areas over a time period of six
months.
Physico- chemical properties of soil viz. soil moisture, bulk density, water
holding capacity, soil pH, soil organic carbon, total nitrogen and total phosphorous
showed marked differences between the fire affected classes themselves and
between control areas. Other soil properties like soil texture, soil electrical
conductivity and total potassium remained without any significant effects after the
fire. Soil physico-chemical properties showed differences between pre-monsoon
and post monsoon season. Soil moisture content (%) decreased with increase in
frequency of fires. In the pre-monsoon conditions, the bulk density of the newly
burnt area increased to 0.94g/cm3
. Water holding capacity of the fire affected areas
at the depth of 0-15 cm increased to 39.23% in pre-monsoon season. Soil pH of the
newly burnt areas increased to 6.85 immediately after the fire. Soil organic carbon
(%) followed the trend (NBP>OBP>CP). Total Nitrogen (%) and total
Phosphorous (ppm) content of the burnt plots was higher compared to the control
area. As vegetation intercepts rain and reduced the kinetic energy of rain water, soil
erosion (Tonnes/ha/yr) of the study area followed the trend (NBP (0.13)> OBP
(0.07)>CP (0.03)).
Total enumeration of regeneration was carried out in the 10m x 10m plots
on a monthly basis. 37 plant species representing 20 families were recorded.
Among them there were 11 tree species, 2 grass species and 4 species of ferns.
Hemidesmus indicus, Pycnospora lutescens and Drynaria quercifolia were found
only in the fire affected plots. The Shannon- Weiner diversity index of saplings in
the month of July are in the range of (1.45-2.37) while it is more for seedlings
(2.76-2.96). The Sorrensen similarity indices of July (0.81(saplings),
0.91(seedlings)) points to the increased number of common species among plots.
The increased evenness and reduced diversity in the fire affected plots are mainly
attributed to the invasion of weeds like Chromolaena odorata, Mimosa diplotricha
and grass species like Pennisetum polystachyon.
Unavoidable physical, chemical and biological changes happening to the soil
after every fire incident are potentially able to influence the soil fauna. Darkling
beetles, broad shouldered water striders and centipedes were recorded only from
the fire affected plots. Ants were present in all the plots in both the seasons. An
increase in the number of individuals was observed after the monsoon. The hard
coated beetles registered their presence in significant number in the burned classes
and the soft bodied animal like earthworm, centipedes and millipedes were absent
immediately after the fire but appeared after the monsoon suggesting that the
temperature variation in the ecosystem might have made them to move away.
The outcomes of present study necessitate longer duration study in different
tropical forest types for more comprehensive understanding of the post fire
dynamics of tropical forest ecosystems.