Abstract
Conspecific adults have strong negative effect on the survival of nearby early-stage seedlings and thus can promote species coexistence by providing space for the regeneration of heterospecifics. The leaf litter fall from the conspecific adults, and it could mediate this conspecific negative adult effect. However, field evidence for such effect of conspecific leaf litter remains absent. In this study, we used generalized linear mixed models to assess the effects of conspecific leaf litter on the early-stage seedling survival of four dominant species (Machilus leptophylla, Litsea elongate, Acer pubinerve and Distylium myricoides) in early-stage seedlings in a subtropical evergreen broad-leaved forest in eastern China. Our results consistently showed that the conspecific leaf litter of three species negatively affected the seedling survival. Meanwhile, the traditional conspecific adult neighborhood indices failed to detect this negative conspecific adult effect. Our study revealed that the accumulation of conspecific leaf litter around adults can largely reduce the survival rate of nearby seedlings. Ignoring it could result in underestimation of the importance of negative density dependence and negative species interactions in the natural forest communities.
Highlights
We hypothesized that conspecific leaf litter could be another important alternative media for the negative effect of conspecific adult neighborhood on seedling survival
We built two types of generalized linear mixed models to address the following questions: (1) Do the amount of conspecific leaf litter significantly affect the early-stage seedling survival of the chosen tree species? (2) If so, can we found this indirect effect by the conventional conspecific adult neighborhood indices? Comparing results of above two analyses could reveal whether the negative effect of conspecific adults on seedlings is underestimated in our natural forest community
Several of our results consistently indicated that the amount of conspecific leaf litter had strong negative effect on early-stage seedling survival of three species (Machilus leptophylla, Litsea elongata and Acer pubinerve)
Summary
We hypothesized that conspecific leaf litter could be another important alternative media for the negative effect of conspecific adult neighborhood on seedling survival. Because the distribution of leaf litter probably largely biased from isotropic shape, the negative effect of adult on seedlings mediated by leaf litter might be anisotropic from the parent tree[25,26,27] This ignored fact of the complex spatial intensity of adult effect on conspecific seedlings proposed a unique challenge to robustly evaluate the importance of conspecific adult effect on seedlings by conventional neighborhood indices in natural forest communities. To overcome this challenge and present the first field examination of whether conspecific leaf litter is an important way to mediate the negative adult effect on conspecific seedlings, observed leaf litter on 561 seedling plots was used to explain the early-stage survival of the seedlings in a subtropical forest.
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