Seed dispersal is a vital link in the processes of seed regeneration, and plays a decisive role in the vegetation restoration of forest ecosystem. Animals are the  important media in the process of seed dispersal and are affected by a variety of factors (including diaspore traits, animal subjects, and environmental conditions, etc.). Forest gap is an important stage of forest cycle.

Furthermore, gap size and within-gap positions are two key features of forest gap structure, and can affect the regeneration of tree species by changing the micro-environment in the forest gap. Most of previous researches have been focused on the effects of forest gaps on animal-mediated seed dispersal by comparing with understory, which have ignored the effects of gaps size and within-gap position.

Some serious problems (e.g., lower timber production, decline in soil fertility and water-conservation function) in larch plantations have threatened their sustainable development. Converting pure larch plantations into mixed larch-broadleaved forests by regulating stand structure (e.g., forming a forest gap) can resolve some of these issues. Hard seeds of Juglans mandshurica Maxim (Manchurian walnut) must be dispersed by animals to the appropriate habitats to remove its seed regeneration obstacles.

Scientists from Secondary Forests Research Group in IAE established two size types of artificial gaps in larch plantations (medium gaps (1.0<D/H≤2.0, D: the average diameter of gaps, H: the average height of gap border trees), and small gaps (0.49<D/H≤1.0)) at Qingyuan Forest CERN, Chinese Academy of Sciences.

We released the labelled walnut seeds at four positions (south, north, east and west) of the gap edges, recorded the fates of seeds, and monitored the animal types for dispersal by using infrared cameras during two continuous growing seasons in 2015 and 2016.

Our results showed that the main disperser of J. mandshurica seeds was Sciurus vulgris in gaps of larch plantations. Gap size and within-gap position only had significant effects on seed removal rate, i.e., seed removal rate in medium gaps was significantly higher than that in small gaps due to the facts that more abundant vegetation resources in medium gaps can attract more animals to forage food; the seed removal rate at the east position of gaps was significantly higher than other three positions. In addition, animals cached more seeds in the understory (33.38%) than in forest gaps (7.00%), which might be because gaps with larger canopy openness could increase the risk of predation of dispersers.

However, we predicted that by comparing with understory, more walnut seeds can germinate and form seedlings in gaps.

Therefore, this research indicated the real effects of gap structures (i.e., gap size and within-gap position) on the animal-mediated seed dispersal, and provided an important reference to improve the ecological functions and sustainable development of larch plantations.

This research was supported by grants from the National Natural Science Foundation of China and the Youth Innovation Promotion Association CAS.

The research “Rodent-mediated seed dispersal of Juglans mandshurica regulated by gap size and within-gap position in larch plantations: Implication for converting pure larch plantations into larch-walnut mixed forests” was published in Forest Ecology and Management.