Tropical lands are degrading rapidly, mainly caused by human deforestation for agricultural land, it might increases
agricultural land but of poor quality since this would affect local and regional ecologies and economies. Desertified
drylands, logged forests, forest fallow and deforested watershed accounts for 43% of the total land, and is greater than
forest land (Parrotta, J.A.et al, 1997). As tropical forest is important in all aspect, restoration on these areas is particularly
urgent.　urgent.　　 Restoration through mixed plantation, monoculture, enrichment plantation and natural succession has be
adopted in Costa Rica, Brazil, Congo, S.Africa and many other tropical countries.

Plantations can facilitates forest succession in their understories by modification of microclimate, accumulation of
humus, removal of growth constraints (Parrotta, J.A. et al, 1997; Lugo, A.E, 1997; Fisher, R.F, 1995). With or without
removal of planted species would gradually results in a floristically rich secondary forest as planted species would be
replace by succession.

It is believed that trees might ameliorate the degraded site as they possess nitrogen fixing and rhizosphere effect,
produce litter and accumulate nutrients to increase fertility and soil organic content. The Organization of Tropical Studies
held the project TRIALS, has tested the amelioration ability of native species, showed that even non-nitrogen-fixing
species contribute to the increment of nitrogen content and organic matter. The changes in surface bulk density, soil
acidity and water content may different under different species indicating that deep-root system may not necessarily
"pump" nutrients (Fisher, R.F., 1995).

Restored by monoculture would be thought as incredible but their structure and management history makes them more
susceptible to wind damage and biotic invasions, and more vulnerable to disturbances and disease (Lugo, A.E, 1997).

Besides, experts tend to depend on fast-growing exotic species with proven management techniques, but native species
is competitive enough to be used in commercial reforestation in tropical forests (Butterfield, R.P. and Fisher, R.F. 1994).
The result of a three-year analysis carried in the Holdridge Tropical Wet Forest lifezone support the argument but more
research is needed to approve large-scale native-plantation program.

The TRIALS has tested the growth of tropical hardwoods on marginal land of northeastern Costa Rica. It proved that
native seeds can sprout and grow well in shadeless areas and adapted to all type of soil even with high aluminum
saturation, and still produce high-density wood (Butterfield, R.P. and Fisher, R.F. 1994; Fisher, R.F., 1995). Though it
appreciates native species in restoration, landowners might not interested in species without a market.

In some tropical areas, wood-based manufacturing industry is chose because of the economic value. It is cost-effective
that tree planting or silvicultural treatment is actively removing carbon dioxide from the atmosphere (Costa, P.M., 1996),
assuming to gain a conservative area and commercial woods at the same time. However, net carbon sequestration by trees
in tropics is much less than actual carbon dioxide assimilation as bulk of wood produced is primarily consumed as fuel
(Dabas, M. et al, 1996).

In determining what species should be planted on the selected sites, one should consider the climatic condition, soil
characteristics after human damage (Kozlowski, T.T., 1985) and species characteristics, as well as the related
microorganisms. Generally, trees need large amount of starch that can be produced by photosynthesis, plenty of water
and mineral nutrients (Kozlowski, T.T., 1985).

Generally, catalytic function of plantation favors fast-growing broadleaf pioneer species to plant in cleared forests.
Native species would be more preferable because exotic seeds may be problematic weed to the surrounding ecosystem
(Parrotta, J.A. et al, 1997; Kozlowski, T.T., 1985), but testing on different landscape with different combinations of
species is necessary (He Dao-quan et al, 1993; Wang Huo-ran, 1994). Market values may sometimes be considered.
　
The introduction of Australia species in China has considered the similarities of the two areas, and was confident enough
to practise vegetative propagation of Eucalyplus. However, with quarantine there still report diseases, revealed that local
disease might hurt them, and the functioning of root nodules would affect by different land quality (Wang Huo-ran et al,
1994). Besides, degradation on tropical lands would require different acidity-adapted species due to geomorphological
differentiation (He Dao-quan et al, 1993). The level of degradation and the kind of activities it is suffered from, and the
objective of restoration should be considered (Hobbs, R.J. and Norton, D.A., 1996; Kzolowski, T.T., 1985).
　
Restoration to restore damaged systems to a defined indigenous ecosystem that resembles the original in all respects.
However, the "natural" once has been destroyed, can hardly be reversed, as the composition, structure and functions of
the altered environment may be irreversible. But nowadays we still have little knowledge about the dynamism of
ecosystem　ecosystem　 (Hobbs, R.J. and Norton, D.A., 1996
　
Restoration of degraded tropical lands can be concluded to be a complicated science involving economic and ecological
aspects needed well management. Characteristics of species, geology, microclimate should be considered, and a well
define objective is of equal importance.
　
　
Reference

Hobbs, R.J. and D.A. Norton (1996), "Towards a Conceptual Framework for Restoration Ecology", Restoration Ecology,
4:93-110

Butterfield, R.P. and R.F. Fisher (1994), "Untapped Potential - Native Species for Reforestation", Journal of Forestry,
1994 (June): 37-40

Fisher, R.F. (1995), "Amelioration of Degraded Rain Forest Soils by Plantations of Native Trees", Soil Sci. Soc. Ami J.,
59: 544-549

Lugo, A.E. (1997), "The Apparent Paradox of Reestablishing Species Richness on Degraded Lands with Tree
Monocultures", Forest Ecology and Management, 99:9-19

Parrotta, J.A. et al. (1997), "Catalyzing Native Forest Regeneration on Degraded Tropical Lands", Forest Ecology and
Management, 99:1-7

Kozlowski, T.T. (1985), "Tree growth in Response to Environmental Stresses," Journal of Aboriculture, 11:97-111

Dabas, M. and Bhatia, S. (1996), "Carbon Sequeatration through Afforestation - Role of Tropical Industrial Plantation",
Ambio, 25:327-330

Costa, P.M. (1996), "Tropical Forestry Practice for Carbon Sequestration: A review and Case Study from Southeast Asia",
Ambio, 25:279-283

Wang Huo-ran et al, (1994), "論澳大利亞植被與中國林木引種的關係", 熱帶地理, 1994:73-81

He Dao-quan et al (1993), "廣東石灰岩地區的森林植被及其恢復問題", 熱帶地理, 13:213-218

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