Plant Diversity and Distribution Pattern in Tropical Dry …
175
at 3 cm above the ground of each individual using vernier caliper. Plant specimens
were collected and identified with confirmation of taxonomist using floras (Gamble
and Fischer 1987; Matthew 1991). The cut stems were enumerated in all the plots
and the disturbance index was computed based on the number of cut stems divided by
the total number of stems including cut stems (Rao et al. 1990). The vegetation data
collected in each plot was analyzed for analytical and synthetic quantitative characteristics. The diversity indices were computed using the freely downloadable PAST
3.1 program (version 3.1; Øyvind Hammer, Natural History Museum, University of
Oslo). Importance value index (IVI) was the sum of the values of relative frequency,
relative density, and relative basal area (Curtis and McIntosh 1950). The abundance
to frequency (A/F) ratio for different species was determined by following Whitford
(1949). The ratio indicates regular (<0.025), random (0.025–0.050), and contagious
(>0.050) distribution pattern.
Some plots (plot nos. 1–10) in the present study were laid near roads, human
settlement or the agricultural fields which are more vulnerable to human exploitation.
Although the study area is a reserve forest, locals frequently cut trees and collect
firewood, lop branches and graze their cattle. Illegal selective cutting of Chloroxylon
swietenia for fencing, agricultural tools and other domestic purposes and Albizia
amara for firewood are quite frequent in this forest. Plots 11–20 are relatively less
disturbed than the other plots. Study plots (plot nos. 21–30) were laid on both the
sides of a rivulet from Ponnaiyar river. In general, the plots near the rivulet are also
subjected to human disturbances. These plots had a rocky terrain. People regularly
use the rivulet for day to day activities. In addition, it also serves as a source of
drinking water for cattle and hence, these plots are also under high anthropogenic
pressures. Soil moisture and pH values showed wide variation among the study plots.
Soil pH ranged from 5.9 to 7.1 and the moisture content ranged from 1.28 to 24.0%.
The mean soil bulk density value of the three layers ranged from 1.21 to 1.82 g/m
3 .
Coarse fragment (>2 mm size) fraction in the soil showed wide variations (33.9%
of samples contain coarse fractions in all the three depths; 10.2% samples contain
coarse fractions in surface (0–10 cm) and middle (10–20 cm) layers; 15.3% samples
contain coarse fractions in middle and bottom layers (20–30 cm); 6.7% samples
have coarse fractions only in the bottom layer) among the plots, samples and depths.
However, 33.9% of the samples collected did not have any coarse fragment (Gandhi
2016; Gandhi and Sundarapandian 2017).
3 Results
3.1 Species Richness and Diversity
A total of 210 plant species belonging to 163 genera and 63 families were enumerated from 30 one-hectare plots in the tropical dry deciduous forest of Sathanur
175
at 3 cm above the ground of each individual using vernier caliper. Plant specimens
were collected and identified with confirmation of taxonomist using floras (Gamble
and Fischer 1987; Matthew 1991). The cut stems were enumerated in all the plots
and the disturbance index was computed based on the number of cut stems divided by
the total number of stems including cut stems (Rao et al. 1990). The vegetation data
collected in each plot was analyzed for analytical and synthetic quantitative characteristics. The diversity indices were computed using the freely downloadable PAST
3.1 program (version 3.1; Øyvind Hammer, Natural History Museum, University of
Oslo). Importance value index (IVI) was the sum of the values of relative frequency,
relative density, and relative basal area (Curtis and McIntosh 1950). The abundance
to frequency (A/F) ratio for different species was determined by following Whitford
(1949). The ratio indicates regular (<0.025), random (0.025–0.050), and contagious
(>0.050) distribution pattern.
Some plots (plot nos. 1–10) in the present study were laid near roads, human
settlement or the agricultural fields which are more vulnerable to human exploitation.
Although the study area is a reserve forest, locals frequently cut trees and collect
firewood, lop branches and graze their cattle. Illegal selective cutting of Chloroxylon
swietenia for fencing, agricultural tools and other domestic purposes and Albizia
amara for firewood are quite frequent in this forest. Plots 11–20 are relatively less
disturbed than the other plots. Study plots (plot nos. 21–30) were laid on both the
sides of a rivulet from Ponnaiyar river. In general, the plots near the rivulet are also
subjected to human disturbances. These plots had a rocky terrain. People regularly
use the rivulet for day to day activities. In addition, it also serves as a source of
drinking water for cattle and hence, these plots are also under high anthropogenic
pressures. Soil moisture and pH values showed wide variation among the study plots.
Soil pH ranged from 5.9 to 7.1 and the moisture content ranged from 1.28 to 24.0%.
The mean soil bulk density value of the three layers ranged from 1.21 to 1.82 g/m
3 .
Coarse fragment (>2 mm size) fraction in the soil showed wide variations (33.9%
of samples contain coarse fractions in all the three depths; 10.2% samples contain
coarse fractions in surface (0–10 cm) and middle (10–20 cm) layers; 15.3% samples
contain coarse fractions in middle and bottom layers (20–30 cm); 6.7% samples
have coarse fractions only in the bottom layer) among the plots, samples and depths.
However, 33.9% of the samples collected did not have any coarse fragment (Gandhi
2016; Gandhi and Sundarapandian 2017).
3 Results
3.1 Species Richness and Diversity
A total of 210 plant species belonging to 163 genera and 63 families were enumerated from 30 one-hectare plots in the tropical dry deciduous forest of Sathanur