Rehabilitation and Restoration Of Degraded Forests (PDF) - IUCN

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Chapter 6: Approaches at the site level see an economic opportunity in the form of apparently unused and unoccupied wasteland. Nonetheless, this approach is probably the most common, and in many situations it is the only one feasible. Reference: Nepstad, Uhl and Serrao 1991; Swaine, Hawthorne and Orgle (1992); Watkins (1993); Berger (1993); Aide et al. (2000) and Case Studies 8.1 and 8.6. 6.2.2 Enrichment planting Not all regrowth or secondary forests have high levels of biological diversity. Many have been disturbed so many times in the past that only a small number of relatively common species remain. In these cases it may be useful to supplement biological diversity by reintroducing certain key species to hasten the process of natural recovery. For example, it might be necessary to quickly increase the population of several particular plant species that would find it difficult to reestablish under the passive restoration approach. These might be endangered plant species, plants with large seeds that are poorly dispersed or plants needed by a particular wildlife species. In some situations exotic monoculture timber plantations have been established but the management objective has changed from exclusive timber production to production plus conservation or sometimes just conservation alone (e.g. Ashton et al. 1997). Enrichment plantings can also be used in situations where exotic monoculture timber plantations have been established but the management objective has changed to production plus conservation or just conservation. Gaps or strips are opened up in the canopy and seedlings of the desired species are planted into them, or seed is directly sown below the plantation canopy. The size of the canopy opening would need to be adjusted to match the tolerances of the species being underplanted. This approach allows some gradual harvesting of the original plantation species, which provides income. It also ensures that a protective forest cover protects the watershed and excludes weeds. The extent to which further canopy openings are created (potentially threatening the underplanted species when the trees are felled) will depend on ecological and economic circumstances. Reference: Ashton et al. (1997). 35
REHABILITATION AND RESTORATION OF DEGRADED FORESTS 6.2.3 Direct seeding In many cases, the rate of natural succession is limited by the slow dispersal of seed across degraded landscapes. An obvious way to accelerate such successions is to deliberately reintroduce the seed. Various forms of direct sowing have been used: in some cases the seed has been broadcast or sown by hand; in others it has been sown from aircraft. Usually the seed must be sown on bare soil so that it can establish quickly in weed-free conditions. Seed reintroduction has been highly developed for use in commercial forestry following post-logging burns; it has also been widely used in mine site rehabilitation projects immediately after mining has ceased and before weeds have become established. It can be carried out after sites have been burned or following a herbicide treatment program to eradicate existing ground cover and shrubs (this might involve limited spraying on strips along which seed is subsequently broadcast or might necessitate complete weed eradication). The advantage of direct seeding is its low cost; there is no need to raise seedlings in nurseries and they can be spread across the landscape easily, including sites that might be difficult to reach when carrying boxes of seedlings. There are several disadvantages, however. There must be no weed competition at the time the seeds are sown, meaning it may only be possible to use the technique in certain specialised situations. In addition, only certain species can be introduced to a site in this way since large amounts of seed are often needed. In many cases only a small proportion of the seed broadcast is usually able to germinate and thrive. Some seed will be lost to seed predators, some will fail to germinate under field conditions and some seedlings will die because of dry weather soon after germination. While such losses can be overcome by increasing sowing rates, seed supplies are often limited, especially seed of uncommon species. Such species may need to be raised in nurseries and planted rather than be directly sown. Reference: Mergen et al. (1981); Allen (1997) 6.2.4 Scattered tree plantings Another way to accelerate successions is to foster the structural complexity that attracts seed- or fruit-dispersing fauna into the degraded 36
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