Analysis of Fragmentation and Anthropogenic Disturbances in the Himalayan Forests: Use of Remote Sensing and GIS
ARC/INFO
environment. Base map at 1:250,000 scale was
prepared from Survey of India toposheet and
information on settlements & primary road
network was extracted from the same map. Road
network was updated through a recent Survey of
India map. Vector data layers were converted to
raster data format with a cell size of 25x25 m (a
pixel size class close to the spatial resolution
of IRS-1C, LISS-III, i.e., 23.5 m) for the use of
landscape analysis. Anthropogenic disturbances
were measured as disturbance index (Anon., 1999)
using a customised software (developed by I.I.R.S,
Dehradun, India) and was computed by adopting a
probabilistic weightage based linear combination
of the landscape attributes.
| Vegetation
| Tone/Colour | Texture
| Physiography | Phenology |
| Riverine
| Medium
Grey | Smooth
| Island
type or near to river, Lowest elevations
| Deciduous |
| Sal
| Dull Red
| Smooth
| Lower
elevation | Green
leaves |
| Pine
| Dark Brown
| Smooth
| Middle
elevation | Green
Leaves |
| Oak
| Brick Red
| Smooth
| Higher
elevation | Green
Leaves |
| Oak mixed
Conifer | Red with
Brown tinge | Uneven
| Highest
elevation | Green
Leaves |
Table 1: Interpretation Key for Major Forest Types using IRS 1C - LISS III FCC.
Shape index (Patton, 1975) was
calculated for various forest fragments. Shape
index (SI) includes perimeter analysis for each
land unit (polygon) to find out edge interaction.
A common feature of fragmentation is a sharp
increase in the amount of induced habitat edge.
The SI describes the deviation of each fragment
from circularity (a perfectly circular fragment
will have a SI value of 1.0 whereas all other
shapes have higher values). SI was calculated
using the formula: SI = P/200 [(pTA)0.5] where TA
=
total area of the fragment (ha), and P = perimeter length (m). The area affected (due to edge impact) was computed (Laurance & Yensen, 1991) using equation:
AA adj = AA x 1- {[ 0.265(AA/TA)]/SI 1.5}
Where AA adj = adjusted affected area of fragment, AA = computed affected area of fragment, TA = total area of fragment, SI = Shape Index of fragment. Remaining core area was calculated by the subtraction of affected area from the total area of fragment.
Results & Discussion
The
forested area in the district Almora accounted for about 42% (1335.97 km
2) of the total area. An elevational difference between ~500m and > 2500m amsl in the mountainous landscape of district Almora has produced a diversity in forest vegetation (Table 2); however, majority of the landscape falls in the altitudinal zone (~1000-1800m) favourable for pine (Pinus roxburghii) dominance in the Central Himalayan region. It is apparent from the spatial distribution of different major forest types (Fig. 2) and area occupied by each type (Table 2) that pine dominated forests are preponderant in the entire landscape of the study area. Pine dominated forest accounts for about 85% (representing 1140.1 km
2) of the total forest while other forest types account for about 11% and 3.5% in case of oak (Quercus spp.) and sal (Shorea robusta) dominated vegetation, respectively. Riverine type in the lowest altitudinal range and oak-conifer type towards the highest altitudinal range are poorly represented on the district landscape.
While there is preponderance of pine forest, occurrence is very fragmentary in nature. A total of 414 forest patches of pine vegetation could be observed in the landscape (Table 3). The area occupied by each fragment varied between <1 km
2 and 179 km
2. The most noticeable feature is that 9% of the area occupied by pine vegetation is fragmented into a very large number (318, accounting for about 77% of the total number of pine patches). The addition of further 67 patches (area between 1-4 km
2) the total area under this category enhances to 17%. This area analyses indicate that the vegetation fragmentation has reached an alarming stage because these small landunits are subject to further degradation and appear to be the possible sites of pine extinction. Smaller units are greater in number as reflected by the fact that fragments having area less than 4 km
2, account for ~ 91% of the total number of fragments. The area covered by these fragments represents ~ 17% of the total area under pine forest. Highly fragmented appearance of pine vegetation is mainly due to the diffused nature of human settlements throughout the landscape. Villagers consume vegetation as firewood and fodder (Singh et. al., 1984, Sharma & Singh, 1994). Functioning of a village ecosystem reveals that firewood accounts for almost hundred per cent of the cooking energy in the domestic sector, and village ecosystem imports about 16 units of energy from the forest to support one unit of agronomic production. To support agronomic production from 1 ha of cropland net primary production of 1 ha of good stocked forest is needed (Sharma & Singh, 1994).
| Forest Type | Area (km2) | % of the Forest | Major Tree Species |
| Riverine | 3.49 | 0.3 | Acacia catechu, Dalbergia
sisso |
| Sal dominated | 46.54 | 3.5 | Shorea robusta, Mallotus philippensis,
Ehretia laevis, Adina cordifolia,
|
| Pine dominated | 1140.10 | 85.3 | Pinus roxburghii, Pyrus pashia,
Engelhardtia spicata, Myrica
esculanta |
| Oak dominated | 142.82 | 10.7 | Quercus leucotrichophora, Quercus
floribunda, Rhododendron arboreum, Lyonia
ovalifolia |
| Oak & Conifers | 3.02 | 0.2 | Quercus semicarpifolia, Cupressus
torulosa, Quercus floribunda, Rhododendron
arboreum, |
Table 2: Major Forest Types and their attributes in District Almora.
Figure 2: Spatial distribution of pine (Pinus roxburghii) forests in the district Almora.
