Causes of Forest Fragmentation and loss of biodiversity. Fragmentation of natural forest areas. Causes of Fragmentation of natural forest areas. Effects of Fragmentation of natural forest areas. The “edge” effect: The cutting of forest into fragments creates many “edges” where previously there was deep forest.
Many species cannot maintain themselves in small fragmented forests. Many large mammals have huge ranges and require extensive areas of intact forest to obtain sufficient food, or to find suitable nesting sites.
Causes of Forest Fragmentation and loss of biodiversity
Fragmentation of natural forest areas. Present day natural forest areas are under various pressures which are mostly human induced. Pressures include fragmentation, area shrinkage and degradation, alien species invasion, grazing, resource extraction etc. Moreover, changes in social structure, resource management also affect grove tradition simultaneously. Fragmentation is one of the major factors which has been causing the isolation and degradation of natural forest areas. Fragmentation stems from population pressure, biomass and agricultural requirement. Once the grove interior is exposed, dry deciduous and light loving members invade the area, thus changing the floral composition as well as micro-climate to great extent. These changes facilitate establishment of the invasive species in the grove area and leaving the endemic members on the verge of extinction. The area shrinkage and changes in climacteric affect the faunal members also. Large to medium size animals cannot stay in a small fragment, those smaller ones which can stay, they also have shortage of resources, shelter etc which ultimately putting constraints on normal life cycle.
Changing social structure plays an important role in gradual declination of natural forest areas. These nature centric worship places in many areas have already been replaced by temples/solid structures in the name of modernization. Once the god/goddess has been shifted to the temple, the surrounding places become irrelevant to the people, thus immediately converted for other usage. As a result, the local shelter for plants and animals as well as ecosystem functioning has been completely lost. Similarly, once the maintenance of the grove is neglected grove condition becomes vulnerable due to various factors. The fragmentation of these patches are general consequence of the haphazard logging and agricultural land conversion which is occurring everywhere, but especially in tropical forests. When these patches are cut into smaller and smaller pieces, there are many consequences, some of which may be unanticipated. Fragmentation decreases habitat simply through loss of land area, reducing the probability of maintaining effective reproductive units of plant and animal populations. Most tropical trees are pollinated by animals, and therefore the maintenance of adequate pollinator population levels is essential for forest health. When a forest becomes fragmented, trees of many species are isolated because their pollinators cannot cross the un-frosted areas. Under these conditions, the trees in the fragments will then become inbred and lose genetic variability and vigor. Other species, which have more wide-ranging pollinators, may suffer less from fragmentation.
Many species cannot maintain themselves in small fragmented forests. Many large mammals have huge ranges and require extensive areas of intact forest to obtain sufficient food, or to find suitable nesting sites. Additionally, their migrations may be interrupted by fragmentation. These animals are also much more susceptible to hunting in forest fragments, which accounts for much of the decline in animal populations. Species extinctions occur more rapidly in fragments, for these reasons, and also because species depend upon each other. The dissection of sacred patches into fragments in certain parts of the Amazon has led to extreme hunting pressures on peccaries, for instance, and in some places where they are locally extinct, three species of frogs have also disappeared, since they depended upon peccary wallows for breeding ponds. The absence of large predator species leads to imbalances in prey populations, and, since many of the prey species are seed-eaters, to declines in the population levels of many plant species. When sacred patches are cut down or burned, the resulting gaps are too large to be filled in by the normal regeneration processes. This permits the ascendancy of rapid-growing, light-tolerant species and grasses. Large gaps may then be converted to scrub or grassland. The “edge” effect: The cutting of forest into fragments creates many “edges” where previously there was deep forest. Many effects are consequent upon this. Edges are lighter, warmer and windier than the forest interior. These changes in micro-climate alter plant reproduction, animal distribution, the biological structure and many other features of the forest. Tree mortality is much greater near edges, and climax species will be replaced by pioneer species. The drier and warmer conditions also make the fragment more flammable, with a concomitant increase in the frequency of fires. Fire is particularly frequent in fragments. Recently, many forests have been subjected to deliberately-set and accidental fires, to which they have little resistance, and to which they are rarely naturally subjected. People often set fire to cut-over areas adjacent to forests to clear them of debris. These fires often get out of control and burn large areas, extend into the forest interior, and inhibit edge regeneration by killing pioneer forest vegetation. More than 90% of forest fires in certain eastern Amazon forest areas were associated with the edges of forest fragments. If conditions remain severe, the forest will recede and be replaced by scrub.
The use of herbicides and the introduction of exotic species into areas surrounding forest fragments are detrimental to forest health. Herbicides blow from cleared agricultural areas into forests, and exotic species introduced by farmers and ranchers spread, often displacing native species. Fragmentation leads to the death of large canopy trees, even in the interior of fragments. Canopy trees dominate the forest structure, and they provide fruits and shelter for many animals. Loss of largest trees has several corollary effects – the alteration of bio geochemical cycles (transpiration, carbon cycles), the reduction of species complexity, and the reduction of fecundity. As mentioned above, large trees are essential habitats and food sources for many other organisms, both plant and animal; they are the source of much of the primary productivity of the forest; and they are responsible for many effects on the water and nutrient cycles. They are irreplaceable in the forest ecosystem.
Natural forest areas are losing species, not only because of the disappearance of their habitat, but also because essential ecological processes are being interrupted by fragmentation. Fragments are much more easily accessible to human incursions than are intact forests. This leads to a variety of extractive activities within the forest interior. Intensive hunting, by depleting animal populations, inhibits plant reproduction, since many seeds can neither be dispersed, nor flowers be pollinated without them. Where these seed dispersers have been eliminated, are at low population densities, or cannot move between forest fragments, seed dispersal will be very limited, and as a result tree species dependent upon animal dispersers may become locally extinct.