Nurse effects of Aloe secundiflora shrubs promote native grass establishment, growth and reproduction in degraded semi-arid rangeland on Koija Group Ranch, north-central Kenya

  • Published source details King E.G. & Stanton M.L. (2008) Facilitative effects of Aloe shrubs on grass establishment, growth, and reproduction in degraded Kenyan rangelands: implications for restoration. Restoration Ecology, 16, 464-474


Making use of potential nurse-effects afforded by native drought-tolerant vegetation in overgrazed, semi-arid areas may facilitate establishment of other desirable native species. This study at Koija Group Ranch (00°33.6′N, 36°54.0′E; north-central Kenya) investigated effects of Aloe secundiflora (a native unpalatable succulent) on Cenchrus ciliaris (a native, perennial, drought-tolerant grass of high nutritional quality for grazing animals) establishment in heavily degraded savannah rangeland.

The study site comprised a fenced 4 ha compound (average 0.8 goats and sheep/ha) with herbaceous cover (around 10%), large areas of bare ground and substantial soil erosion. Absent were several palatable perennial grasses present in less over-grazed areas. In the 25 x 5 m experimental block (within the compound) there was less than 1% perennial vegetation cover and a cement-like soil surface.

Along nine (1.2 m long, 2.5 m apart) rows, 21 holes (14 cm diameter by 25 cm deep, 20 cm apart) were excavated. Each set of seven adjacent holes was randomly assigned a ‘neighbour’ treatment, adjacent to which C. ciliaris seed was planted in April 2002 (before seasonal rain onset): 1) seven transplanted mature aloes; 2) seven thorny Acacia branch piles (similar dimensions providing similar physical protection to aloes); 3) seven refilled hole (control).
Grass performance was monitored over the subsequent three growing seasons.

In the first growing season C. ciliaris seedling emergence was low (average 2.6% across treatments, not varying significantly among treatments). No new seedlings were observed subsequently. At the end of the first season, 16% of seedlings in the aloe treatment, 9% in the thorn treatment and 6% in the controls were alive. Thereafter, C. ciliaris survival was 98% in the second and 90% in third seasons, and was similar among treatments.

During the first growing season, the aloe treatment significantly improved size of individual grass plants and had greatest grass abundance and cover in all three seasons. The control had poorest performance. The results indicate that planting aloes can improve the effectiveness of C. ciliaris reseeding, exceeding that of the more common strategy of using thorn branch piles.
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