Effect of fallow period on soil seed bank runoff and regeneration of successional forests

In humid subtropical forests, the age of shifting cultivation fallow dramatically influences seed runoff patterns, which in turn plays a crucial role in forest regeneration. To explore into this complex relationship, we investigated the variation in soil seed bank runoff in different shifting cultivation fallow and reference forest (SF₀₃: 0 − 3 years fallow, SF₀₇: 4 − 7 years fallow, SF₁₁: 8 − 11 years fallow, SF₁₅: 12 − 15 years fallow, RF: reference forest). An area of 2 × 2 m was demarcated inside the experimental plots. The runoff water and sediments were collected in a big container to determine the seed losses through runoff water. Viable seeds were estimated using the seedling emergent method. A total of 2,456 seeds were runoff from the experimental sub − plots. Among the SFs, SF₀₃ lost a total of 216 seeds (m^− 2) whereas the RF lost only 72 seeds (m^− 2) through runoff. The SF₁₅ had higher species richness (S) and Shannon diversity index (H’) than RF. The highest value for the Sorensen Similarity Index (SSI %) for trees was observed between SF₀₃ and SF₀₇. From the population flux study of Ageratum conizoides, it was concluded that the young SF has higher seed runoff. We observed variation in soil seed bank runoff (p ≤ 0.01). Our results depict that the younger SFs lose a higher number of seeds and are mainly composed of pioneer species. However, with the increase in age of fallow the composition of species shifted to tree component and has a higher value of diversity index. This revealed the progressive sign of regeneration with the increase in age of fallow.