Study

Forest restoration in abandoned agricultural land: a case study from East Africa

  • Published source details Chapman C.A. & Chapman L.J. (1999) Forest restoration in abandoned agricultural land: a case study from East Africa. Conservation Biology, 13, 1301-1311.

Summary

Remaining tropical forests are increasingly threatened by deforestation and degradation. Deforested areas are often converted to agricultural land which after a few years, is generally unproductive. Reforestation of such areas to something resembling the former native forest would be a desired conservation goal. In a 4-year study, the pattern of forest recovery following clearing and 3 years of cultivation of a moist-evergreen forest in Uganda was quantified. As part of this study, an assessment was made of two management programmes designed to enhance restoration of this abandoned agricultural land: i) planting cuttings to provide perches for seed-dispersing bird species thus acting as 'seed dispersal foci', and ii) sowing tree seeds.

Study site: The study was undertaken in Kibale National Park (766 km²) western Uganda, (0°13'–0°41'N, 30°19'–30°32'E) in an area of abandoned agricultural land that prior to clearance was classified as a Parinari forest.

Treatments:The effectiveness of two potential methods of enhancing forest regeneration were assessed in two 20 × 40 m plots and a similarly sized control plot (no cuttings planted, no seeding) for comparison:

i) planting cuttings to act as foci for seed dispersal - two Erythrina abyssinica and three fig Ficus spp. (F.brachylepis, F.natalensis, F.dawei) 1.5 m tall cuttings were planted in each 10 × 10 m subplot.

ii) sowing seeds of 'pioneer' species or species commonly found growing in disturbed areas around Kibale: Albizia grandibracteata (100 seeds/subplot, for a total of 800 seeds); Cordia abyssinica (100 seeds/subplot, for a total of 800 seeds); Trema orientalis (400 seeds/subplot, for a total of 3,200 seeds); and Maesa lanceolata (400 seeds/subplot, for a total of 3,200 seeds). The number of seeds used was based on seed size (more for small-seeded species) and availability.


Seedling growth and mortality, dominant cover, frugivore visitors, and rodent abundance was quantified.

Both methods used, i.e. sowing tree seeds and planting cutting, failed to enhance forest regeneration on the abandoned agricultural land: the density of tree seedlings growing in the sown management plot (0.35 seedlings/m²) and in the plot where cuttings were planted (0.30 seedling/m²) was infact lower than in the control plot (0.51 seedlings/m²).

Conclusions: Planting of cuttings to act as bird perches for frugivorous seed-dispersing species (thus acting as potential seed dispersal foci) and sowing of seeds, were designed to increase seed input, a factor often identified as limiting forest recovery. However, the time when the sown seeds were probably germinating corresponded to the period of highest rodent density which may have resulted in high seedling mortality. Sowing during a period of low rodent density may have yielded better results, but further studies would be needed to elucidate this.

Unfortunately, also, during the first 2 years when the cuttings were used as perches, rodent density remained high and seedling recruitment was low. However, when rodent density subsequently declined, elephant grass Pennisetum purpureum became dominant and grew to form a canopy above the cuttings and effectively prevented tree seedling recruitment.


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:

http://www.blackwell-synergy.com/doi/full/10.1046/j.1523-1739.1999.98229.x

 

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