Indigenous Vs Exotic Species

CHOICE OF SPECIES INDIGENOUS VS EXOTIC

CHOICE OF SPECIES

            The term “choice of species” clearly implies the possibility of a selection from a number of potential candidates, with the list of possible trees being drawn from:
1.     Literature
2.    Eco-physiological tests
3.    Field trials
FACTORS AFFECTING THE CHOICE OF SPECIES:
·       Ecological factors
·       Suitability to Soil and Moisture Conditions
·       Succession
·       Generic Factors
·       Relative Costs
PURPOSE OF PLANTATION:
1.     Industrial Uses
2.    Domestic Uses
3.    Environmental Uses
4.    Tree planting as an Integral Part of Other land uses

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INDIGENOUS SPECIES:

          “An indigenous species is one that grows naturally in the country, concerned though, not necessarily in all parts and certainly not suited to all sites.”

 Advantages of Indigenous Species:
1.     The growth of natural stands provides some indication of possible performance in plantation
2.    The species is adapted to the environment and already filling and ecological niche.
3.    I. Species, even in monoculture are generally considered more ecologically valuable than exotics for the conservation of native fauna and flora.
4.    The timber is likely to be known to local wood-using industries.
          For these reasons, if an indigenous spp grows well in a plantation on the sites for afforestation there is no compelling reason to widen the choice. E.g. Acacia nilotica in Sindh.
EXOTIC SPECIES:
            “The term exotic in forestry lakes a generally accepted definition simply ‘any species grown outside its natural range or distribution’”.
Need and importance of Exotics:

          Pakistan is spending a lot of foreign exchange on the import of timber on the import of timber and timber products annually, while the demand for the same is still increasing rapidly with the expansion of wood-based industries and rise in the standard of living. It is therefore imperative, that all its resources are fully exploited to achieve self-sufficiency in forest products. The production can be increased by putting more area under forest and by introducing fast-growing exotic species.
Properties of Successful exotics:
         
          Often, however, exotic plantations are formed on open grasslands sandy waste or another tract devoid of a forest, and here their creation is an advantage rather than otherwise, apart from utilitarian considerations.
          The exotic trees grown in commercial forests for the production of wood have the following properties:
i.                their produce is of high value
ii.              their rate of yield is high
          In addition to these, exotic trees have the following properties in common:
i.      An adequate supply of seeds (or cuttings) is available
ii.    They are easy to raise in nurseries.
iii. They are easy to establish and grow in plantations
iv.  Insects or diseases do not prevent their successful growth
v.    Information is available on methods of growing them and on their rate of growth and yield.
TRIALS FOR INTRODUCTION OF EXOTICS:
          The procedure adopted in Nigeria, Uganda, and Zambia for the introduction of exotic species has been quite successful and is recommended for use in other arid zones.
Steps Involved:

i.               The Species Elimination Trials
          The trial is designed to eliminate from further consideration those species clearly unsuited to the environment of the new planting area.
            Species elimination trials in Nigeria have given sufficiently reliable information to eliminate about half the species at a reasonable cost after two years.
ii.            The Species Growth Trial
             The growth trial provides information on performance, growth rate, stem and crown form, agencies causing injury or death, and crop benefits to be derived from those species emerging successfully from elimination trials.
             Growth trials are established on different soil types and different climatic zones of the region.
iii.         Species Plantation trials
                      Comparison of different spacing, fertilizers, cultivation and other silvicultural treatments should be made on trial plots designed for that purpose. The species, which pass this test and meet the desired purpose, may then be recommended for field planting.
iv.          Species Trials in Pakistan and Some Results

          The indigenous plant species have evolved through long and continued selection and probably are the best suited to the local environment i.e. in a plain and arid area following species are grown Prosopis spicegera, Salvadora oleoides, Tamarix articulate, Acacia Senegal, Zizyphus jujuba and Tecoma  undulata
FOLLOWING ARE THE EXOTIC SPECIES FOUND IN PAKISTAN:

1.    Eucalyptus spp.
Out of a number of species of Eucalyptus spp tried during past half century, Eucalyptus camaldulensis, E. citriodora, E. rudis, and E. terticornis have done best. These spp can easily be grown with irrigation in the plain.
2.  Populus spp.
Poplars are among the fast-growing trees in the world. The indigenous spp Populus ciliate, P. alba, P. euphratica, P. deltoids, P. euramericana occur in various areas.
3.  Acacias:
Several Australian species have done well in the hills of India but they have not so far succeeded in Pakistan. But the African spp, notably Acacia tortilis and Acacia nilotica praise for dry zone.
4.  Prosopis juliflora:
It is most successful introduction for really dry and saline/alkali sites and with the allied busy farm, P. glandulosa has become naturalized in some areas.
5.   Broussonetia papyrifera, Ailanthus excela and Robinia pseudoacacia :
These are the most successful exotics in Pakistan. The spp are extensively used in protective afforestation in the less arid uplands.
6.  Casuarina equisetifolia:
It occurs on coastal sands and has been very successfully planted on similar sites outside its probable natural range. It has also been extensively planted far from the coast and on a wide variety of soil.
SPECIES RECOMMENDED FOR VARIOUS ZONES:
1.    Northern Hilly Tract: Poplus deltoides, Robinia pseudoacacia.
2.   Sub-Mountain Range: Eucalyptus tereticornis
3.   Western Hilly Areas: Poplus deltoides, Eucalyptus spp.
4.   Indus plain: Acacia cyanophylla, A. tortilis, Eucalyptus camaldulensis, Leucaena leucocephala (iple iple), Poplus euramericana.
5.    Deserts: Acacia aneura, A. tortilis, A. Victoria, Prosopis juliflora, P. cineraria.
6.   Saline Areas: A. nilotica, A. cyanophylla, E. camaldulensis, E. microtheca, Leucaena leucocephala, Prosopis juliflora.

7.    Waterlogged Areas: E. camaldulensis, E. robusta.
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