Effects of tree density and herbaceous plants on tree seedling survival across the growing and non-growing season in a temperate forest

Abstract

Tree seedling survival is critical for estimating forest recruitment, but it remain elusive about how neighboring tree’s density and herbaceous plants affect it. To assess the relative importance of tree density and herbaceous plants on tree seedling survival during the growing season and non-growing season, we established a two-year experiment with seedling census and removal of herbaceous plants in both secondary and old-growth temperate forest sites in the temperate forests of northeastern China. A total of 3,443 seedlings in 17 tree species were surveyed in this study. We found that both tree density and herbaceous plants significantly affected tree seedling survival, but the specific effects depended on shade tolerance, seedling growth stage and growing season. Conspecific adult neighbors had significant negative effects on the survival of shade-tolerant seedlings during the growing season, while conspecific seedling densities positively correlated with shade-intolerant seedlings. Herb removal significantly improved the survival of newly germinated and shade-intolerant seedlings during the growing season. Furthermore, we found that the survivals of both newly germinated and established seedlings differed seasonally in response to adult, seedling neighbors and herb removal. Herb removal enhances seedling survival during the non-growing season by offsetting the negative effects of conspecific adult neighbors during the growing season. Our findings provide new evidence for seedlings’ shade tolerance, growth stage and seasonal dependence of density dependence in temperate forests, and highlight the significance of herbaceous plants for seedling survival, an important factor that has been neglected in many previous studies.