Size-Dependent Patterns of Seed Rain in Gaps in Temperate Secondary Forests, Northeast China

Qiaoling Yan,Qun Gang,Jiaojun Zhu

doi:10.3390/f10020123

Abstract

Secondary forests have become the major forest type worldwide, and are experiencing various disturbances and exhibiting obvious vegetation degradation (e.g., reduced biodiversity and decreased productivity) compared with primary forests. Forest gap is a common small-scale disturbance in secondary forests. Promoting natural regeneration under gap disturbance is an important approach to recover biodiversity and ecosystem services for temperate secondary forests. The gap size is the crucial characteristic controlling natural regeneration of many tree species. However, little is known about the spatiotemporal pattern of seed rain for gravity-dispersed and wind-dispersed tree species in gaps of varying sizes. The objectives of this study were to determine how seed rain of dominant tree species depend on gap size, and consequently, to explore some gap-based silviculture solutions for restoring secondary forests from the view of seed dispersal. The spatial distribution of seed rain in gaps with three sizes (large gaps of 250–350 m2, medium gaps of 150–250 m2, and small gaps of < 150 m2), the temporal dynamics of seed rain over three years, and the relationship between seed rain and soil seed banks were explored in temperate secondary forests. The results showed that more than 90% of the seeds in seed rain were wind-dispersed, and their seed rain density and the contribution of seed rain to soil seed bank in medium gaps reached the highest (p = 0.03). The results suggest that establishing medium-sized gaps (i.e., gap size with 150–250 m2) in the secondary forests is more favorable for improving the natural regeneration potential (arrival of seeds and forming soil seed bank) of gap-dependent and wind-dispersed species (e.g., Acer mono) in gaps.

Highlights

Secondary forests have become the major forest type worldwide, and have currently accounted for more than 50% of the total forest area of China [1]
The results suggest that establishing medium-sized gaps in the secondary forests is more favorable for improving the natural regeneration potential of gap-dependent and wind-dispersed species (e.g., Acer mono)
Because seed traps were used to collect the seed rain, only the fruits/seeds after the first dispersal were considered [26], and the effects of gap size on the dispersal of zoochorous seeds were not explored in this study

Summary

Introduction

Secondary forests have become the major forest type worldwide, and have currently accounted for more than 50% of the total forest area of China [1]. One-third of the national forests are distributed in Northeast China, more than 70% of which have become the secondary forests due to a century of excessive timber harvesting [2]. Secondary forests are derived from natural regeneration after the original forests suffering from the destructive disturbances [1] and are presenting obvious vegetation degradation (e.g., reduced biodiversity, decreased productivity) [3]. It is one of the top priorities for forest managers to restore the structure and function of secondary forests by promoting natural regeneration [1,4,5,6]. The natural regeneration of plants involves several stages (i.e., seed rain, seed bank, seedling bank, sapling bank and advance regeneration) and is considered to Forests 2019, 10, 123; doi:10.3390/f10020123 www.mdpi.com/journal/forests

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Conclusion