This section discusses the problems that have been encountered due to the introduction of invasive plant and animal species in Pakistan.
Biological invasion by alien introduced species is one of the major threats to the native biological diversity of a region. The impact of invasive species on the native species is immense and irreversible on a global scale. Climate change, environmental pollution and habitat degradation are encouraging intentional and unintentional introductions to establish themselves in modified habitats.
The scope and cost of biological invasion is global and enormous, both in ecological and economic terms. Invasive species are found in all taxonomic groups including viruses, fungi, mosses, ferns, higher plants, invertebrates, amphibians, reptiles, birds and mammals. They have invaded and affected native biota in virtually every ecosystem of the earth. The ecological cost is the irretrievable loss of native species and ecosystems. The economic costs run into billions of dollars spent to control arable weeds, insect pests and pathogens.
A comprehensive legal and institutional framework is required to deal with this issue to effectively control the flow of alien species. There is very little awareness among the general public and government sector about the magnitude and economic costs of the problem.
Brief definitions of some important terms frequently used with reference to invasive species are given in the IUCN Guidelines for the Prevention of Biodiversity Loss Due to Biological Invasion are given below:
"Native species" (indigenous) means a species, subspecies, or lower taxon occurring within its natural range and dispersal potential (i.e. within the range it occupies naturally or could occupy without the direct or indirect introduction or care by humans).
"Alien species" (non-native, non-indigenous, foreign, exotic) means a species, subspecies, or lower taxon occurring outside of its natural range and dispersal potential (outside the range it occupies naturally or could not occupy without direct or indirect introduction or care by humans). This term includes any part, gametes, or propagules of such species that might survive and subsequently reproduce.
"Invasive species" means an alien species which has become established in natural or semi-natural ecosystems or habitats, is an agent of change that threatens native or biological diversity. Although the BAP deals with the issues of invasive species, However there is poor understanding of these issues in Pakistan. It is hoped that this report will be a guideline to Biodiversity related decision-makers to address the issues through projects. However, it will take time to fully integrate this issue into the existing legislation and policies.
14.2 Introduced Eucalyptus Species
Eucalyptus is native to Australia and was introduced in Pakistan almost one hundred years ago. There are more than 600 species of eucalyptus. Four namely Eucalyptus camaldulensis, Eucalyptus citriodora, Eucalyptus territicornis and Eucalyptus microtheca, have adapted to local conditions. However, only Eucalyptus camaldulensis is widely grown on farmlands for commercial purposes. Eucalyptus (Eucalyptus camaldulensis) belongs to family Myrtaceae and is now widespread in the problem soils of Pakistan. Many exotic eucalyptuses were tried and introduced in irrigated plantations as well as linear land strips. Eucalyptus camaldulensis is fully established in Pakistan and is widely grown on farmlands and in public forests. In addition, seeds profusely every year. It partly sheds leaves and is an evergreen broad-leaf. It is a non-legume nitrogen-fixer and substantially improves the sterile, waterlogged, and saline/alkaline soils. It grows in a wide range of climates and soil types, and has environmental value due to its evergreen characteristics.
Eucalyptus has established itself in Pakistan and can be seen everywhere from the mountains to the seacoast. Although it does not occupy a large area, eucalyptus is found everywhere in Pakistan except the high hills. It is found in areas such as marginal and sub-marginal farmlands, scrub forests, Pabbi Hills, Salt Range, Thar and Cholistan Desert, piedmont tract of the Salt Range and the Sulaiman Range. Additionally, it is found in the plains of Punjab, Sindh, NWFP and Balochistan. Eucalyptus can be seen growing and contributing to conservation, good air, and the production of honey and soil environment. This is done because eucalyptus firewood now sells, thereby mitigating the pressure on the local firewood species. Despite the claims of the anti-eucalyptus campaigners, birds roost and nest on this tree, and the honeybees flock to collect its nectar.
This species is also found in the linear land strips and village surroundings and grazing lands. Most of the man-made irrigated plantations have sizeable areas under Eucalyptus camaldulensis. At least 7.7 million cf. of eucalyptus biomass was estimated in 1992 (FSMP, 1992). The Sindh province alone has 6,000 ha of land under this species.
There is lot of controversy surrounding the monoculture of Eucalyptus camaldulensis. For example, in Malakand, lower Swat Valley, and Siren Valley, natural vegetation has been totally replaced by eucalyptus plantations. Natural vegetation can not grow under eucalyptus. Consequently, the natural habitat will be totally degraded, and wildlife normally seen around indigenous plant species in the area will disappear.
Eucalyptus camaldulensis has fully adapted to the edapho-climatic conditions of Pakistan. Even in piedmont soils like the one prevailing in the Jauharabad Plantation, regeneration from seed has been observed.33 It has an excellent coppicing power and ratoon34 cropping can be practised for pulp and small timber.
14.2.1 Allelopathic35 Affects
Experiments at Punjab Forestry Research Institute (PFRI) Faisalabad (Fauzia, 1992 and Rafique, 1993) have confirmed that Eucalyptus camaldulensis has no adverse allelopathic affect on wheat crop. However, it competes for moisture, nutrients and light and must be properly planted in farmlands.
14.2.2 Ecological Impact
Eucalyptusis believed to compete with local flora for nutrients and outpaces all other in drawing water from deeper soils, resulting in the drying up of the subsoil water table. Still, more data that is scientific is required on this issue.