Factors limiting the recruitment of artificial black locust forests in extremely arid environment

Afforestation is a common ecological practice for solving drought issues. However, unclear regeneration mechanisms in the context of drought jeopardize artificial forests. Sexual and asexual reproduction (seeds, seedlings and resprouts) in an artificial black locust forest on the Loess Plateau of China (LPC) were investigated to better understand the recruitment limitations of artificial forests in an extremely arid environment. This study found that the thousand kernel weight of black locust was 16.97 g (+/- 1.19) on the LPC, which was lighter than that reported in other regions. The proportion of undamaged seeds on the trees was 83.56% (+/- 6.29), although this value reduced to 17.47% (3.48) when the seeds fell to the litter layer and ground surface. The germination rate of undamaged seeds in the laboratory environment was 79.66% (+/- 12.61) on average. Thus, a low seed weight will not reduce the germination rate in suitable environments but will most likely lead to reduce the ability of keeping health after the seeds drop to the litter layer. The reproduction of artificial black locust forests in the extremely arid environment was also low, with 467.86 individuals/ha on average. The quantity of sprouts of a larger size was more than that of seedlings. The results further indicated that reproduction was affected by deficiencies in water and available nutrients and competition for resources from aboveground vegetation. The disturbance intensity was good for resprouts. Seedlings and resprouts self-clumped at scales of 1-7 m and 0-4.5 m, respectively. Seedling recruitment declined near adult trees, while resprouts survived better near adult trees. We suggest that drought- and low nutrient-resistant cultivars and planting on gentle slopes should be implemented to improve recruitment in the studied forest. Moreover, asexual reproduction may be improved via forest management.