Mine Closure - Mining and the Environment: From Ore to Metal - page 819

For effective erosion control,
groundcover at or close to 100%
is preferred.

The ground coverage that can be expected from cover crops depends largely on climatic
factors, particularly rainfall. For effective erosion control, groundcover at or close to 100%
is preferred. In tropical areas and in wetter parts of the temperate climatic zones, coverage
of 100% in the i rst wet season can usually be achieved. In arid areas, such coverage can
only be achieved by means of regular watering. If practicable, such watering in the i rst
year can certainly be most benei cial. However, for economic reasons, watering is seldom
continued beyond the i rst year.

Species Selection

For rehabilitation programmes aimed at restoring natural vegetation, most if not all the
species planted will be those that occur naturally in the immediate vicinity. For many of
these species, seeds can be harvested manually and either planted directly or i rst estab-
lished in a nursery, prior to planting ( Figure 21.3 ). For those species from which seed
cannot be readily harvested or that defy attempts at germination, natural seedlings are
sometimes excavated and grown in pots in a nursery before being planted out. As men-
tioned previously, there is a practical limit to the number of species that can be planted in
any given situation. Many more species will appear over time, either from seeds stored in
the topsoil (if applied), by invasion from nearby areas, or introduction by birds.
Considerable controversy attends the use of introduced or exotic species in situations
where natural vegetation is to be established. This is because of the severe and widespread
ecological damage that has been caused by many exotic species introduced for agricul-
tural or decorative purposes. Outside their natural habitat where populations are control-
led by natural mechanisms, many species proliferate at the expense of more vulnerable
native plants. However, there are situations where plants suitable for rapid revegetation
of a given site, are not readily available within the local natural plant community. In such
cases, the use of introduced species may be considered. Any introduction of exotic species
should only be made after careful consideration of the characteristics and requirements of
both the candidate introduced species and the species to be established in the longer term.

Outside their natural habitat
where populations are controlled
by natural mechanisms, many
species proliferate at the
expense of more vulnerable
native plants.

CASE 21.4
Rehabilitation at Mt Muro Gold Project in Indonesia

The Mt Muro Gold project in Central Kalimantan, Indonesia
involved mining of multiple small pits. Waste rock was
used partially as pit back-fi ll and was also placed in six
waste rock dumps which were constructed primarily using
bottom-up methods, and were rehabilitated progressively.
Accordingly, by the time that operations ceased in 2002,
considerable experience had been gained, and rehabilita-
tion procedures had been well established. The target land
use for rehabilitated land, as required by the Ministry of
Forests was for Production Forest, and revegetation pre-
scriptions were directed to this end. Following placement
of topsoil, a legume seed mixture was applied as initial

groundcover. Subsequently, in the second year, seedlings of
fast growing tree species, including an Albizzia sp
and a Eucalypt, were planted. Monitoring indicated that
100% groundcover was achieved in the fi rst year and
maintained thereafter. After fi ve years, (see photo) the
fast growing timber trees had reached more than 10 m in
height and provided a canopy cover of more than 50%.
Furthermore, the initial cover crop legumes had all but
disappeared and volunteer species, including ferns substan-
tially outnumbered the planted species. Local people had
already commenced harvesting of the most advanced trees
(Albizzia).