Facilitative Effects of Aloe Shrubs on Grass Establishment, Growth, and Reproduction in Degraded Kenyan Rangelands: Implications for Restoration

摘要

Under the harsh environmental conditions present in severely overgrazed, semiarid rangelands, facilitator plants offer a promising tool for ecological restoration. This study investigated facilitative effects of Aloe secundiflora-a native drought-tolerant, unpalatable, thorny shrub-on grass establishment in degraded rangelands in Kenya. We planted native perennial grass seeds adjacent to three neighbor treatments: transplanted mature aloe shrubs, piles of thorn branches that provided similar physical protection to aloes, and control treatments with no facilitator. We monitored grass performance for three growing seasons. During the first growing season, association with aloe shrubs significantly improved seedling survival and plant size of individual grasses, whereas grass survival in thorn treatments was intermediate between aloe and control treatments. At the population level, aloe neighbor treatments were associated with the greatest grass abundance and cover in all three seasons and reproductive output in the second season. Control treatments were associated with the poorest grass performance for all three variables. The findings indicate that planting aloes can improve the effectiveness of grass reseeding for rangeland restoration, exceeding the benefits gained from the more common strategy of using thorn branch piles. The utility of aloes in particular is further enhanced by the economic value of these plants; medicinal sap can be sustainably harvested from aloes planted for restoration.